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 Document TECOGEN INC. 76 Treble Cove Road Building 1 North Billerica, Massachusetts 01862 July 15, 2025 VIA EDGAR United States Securities and Exchange Commission 100 F Street, N.E. Washington, D.C.  20549 Attn:    Aliya Ishmukhamedova, Esq. Division of Corporation Finance Office of Technology Re:    Tecogen Inc.     Form S-1 Registration Statement     ( File No. 333-288668)      Acceleration Request :     Requested Date: July 17, 2025     Requested Time: 5:00 p.m. Eastern Time Ladies and Gentlemen: Pursuant to the requirements of Rule 461 under the Securities Act of 1933, as amended, Tecogen Inc., a Delaware corporation (“Company”) , hereby respectfully requests acceleration of the effective date of the Company’s Registration Statement on Form S-1 (File No. 333-288668) filed with the Securities and Exchange Commission on July 15, 2025, to 5:00 p.m. (Eastern Time) on July 17, 2025 , or as soon thereafter as practicable. If you have any question regarding the foregoing, please contact Neil R.E. Carr, Esq., of the law firm of Somertons, PLLC, our outside legal counsel, at 202.459.4651 or by email at neil.carr@somertons.com. Respectfully submitted, /s/ Abinand Rangesh Abinand Rangesh Chief Executive Officer cc:    Neil R.E. Car, Esq.     Somertons, PLLC

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 Document Roth Capital Partners, LLC 888 San Clemente Drive, Suite 400 Newport Beach, CA 92660 July 15, 2025 VIA EDGAR CORRESPONDENCE United States Securities and Exchange Commission 100 F Street, N.E. Washington, D.C.  20549 Attn:    Aliya Ishmukhamedova, Esq. Division of Corporation Finance Office of Technology Re:    Tecogen Inc. Registration Statement on Form S-1 File No. 333-288668 Ladies and Gentlemen: Pursuant to Rule 461 of the General Rules and Regulations under the Securities Act of 1933, as amended (the “Act”), we, the underwriter, hereby request that the Securities and Exchange Commission (the “Commission”) take appropriate action to cause the above-referenced registration statement on Form S-1 (the “Registration Statement”) to become effective at 5:00 p.m., Eastern Time, on Thursday, July 17, 2025 or as soon thereafter as practicable. Pursuant to Rule 460 under the Act, we wish to advise you that we have distributed as many copies of the Preliminary Prospectus dated July 15, 2025, to agents, dealers, institutions and others as appears to be reasonable to secure adequate distribution of the preliminary prospectus. The undersigned, as underwriter, has complied and will comply with Rule 15c2-8 under the Securities Exchange Act of 1934, as amended. If you require any additional information with respect to this letter, please contact Ali Panjwani at (212) 326-0820 of Pryor Cashman LLP. Very truly yours, ROTH CAPITAL PARTNERS, LLC By: /s/ Aaron M. Gurewitz _________________ Aaron M. Gurewitz President cc:    M. Ali Panjwani, Esq.     Pryor Cashman LLP

<DOCUMENT>
<TYPE>TEXT-EXTRACT
<SEQUENCE>2
<FILENAME>filename2.txt
<TEXT>
 July 1, 2025

Abinand Rangesh
Chief Executive Officer
TECOGEN INC.
76 Treble Cove Road
Building 1
North Billerica, MA 01862

 Re: TECOGEN INC.
 Draft Registration Statement on Form S-1
 Submitted June 26, 2025
 CIK No. 0001537435
Dear Abinand Rangesh:

 This is to advise you that we do not intend to review your registration
statement.

 We request that you publicly file your registration statement at least
two business
days prior to the requested effective date and time. Please refer to Rules 460
and 461
regarding requests for acceleration. We remind you that the company and its
management are
responsible for the accuracy and adequacy of their disclosures, notwithstanding
any review,
comments, action or absence of action by the staff.

 Please contact Aliya Ishmukhamedova at 202-551-7519 with any questions.

 Sincerely,

 Division of
Corporation Finance
 Office of
Technology
cc: Neil R.E. Carr
</TEXT>
</DOCUMENT>

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TECOGEN INC.

45 First Avenue

Waltham, MA  02451

Tel: (781) 466-6400

April 21, 2020

VIA EDGAR

United States Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C.  20549

Attn:    Bernard Nolan, Esq.

Attorney Adviser

Division of Corporation Finance

Re:    Tecogen Inc.

Form S-3 Registration Statement

File No. 33-237582

Ladies and Gentlemen:

Pursuant to the requirements of Rule 461 under the Securities Act of 1933, as amended, Tecogen Inc., a Delaware corporation, hereby respectfully requests acceleration of the effective date of its Registration Statement on Form S-3 (File No. 333-237582) filed with the Commission on April 6, 2020, to 4:00 p.m. on April 23, 2020, or as soon thereafter as practicable.

If you have any question regarding the foregoing, please contact Neil R.E. Carr of the law firm of Somertons, PLLC, at (202) 459-4651 or by email at neil.carr@somertons.com.

Respectfully submitted,

/s/ John K. Whiting, IV

John K. Whiting, IV

General Counsel

cc:    Neil R.E. Carr, Somertons, PLLC

April 10, 2020
Benjamin M. Locke
Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451
Re:Tecogen Inc.
Registration Statement on Form S-3
Filed April 6, 2020
File No. 333-237582
Dear Mr. Locke:
            This is to advise you that we have not reviewed and will not review your registration
statement.
            Please refer to Rule 461 regarding requests for acceleration.  We remind you that the
company and its management are responsible for the accuracy and adequacy of their disclosures,
notwithstanding any review, comments, action or absence of action by the staff.
            Please contact Bernard Nolan, Attorney-Adviser, at (202) 551-6515 or, in his absence,
Jan Woo, Legal Branch Chief, at (202) 551-3453 with any questions.
Sincerely,
Division of Corporation Finance
Office of Technology
cc:       Neil R.E. Carr

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April 11, 2017

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Attention:    Ms. Pamela Long, Assistant Director

Ms. Kate McHale, Staff Attorney

Ms. Asia Timmons-Pierce, Staff Attorney

Mr. Dale Welcome, Staff Accountant

Ms. Anne McConnell, Staff Accountant

Re:     Tecogen Inc.

Registration Statement on Form S-4

Originally Filed on December 21, 2016

Amendment No. 3 Filed April 11, 2017

File No. 333-215231

Ladies and Gentlemen:

In accordance with Rule 461 under the Securities Act of 1933, as amended, the undersigned respectfully requests that the effective date for the Registration Statement referred to above be accelerated so that it will be declared effective at 4:00 PM, April 12, 2017 or as soon thereafter as is practicable.

Very truly yours,

Tecogen Inc.

By: /s/ David A. Garrison

David A. Garrison

Chief Financial Officer

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March 24, 2017

Via EDGAR

Pamela Long, Assistant Director

Securities and Exchange Commission

Office of Manufacturing and Construction

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc.

Amendment No. 1 to Registration Statement on Form S-4

Filed on January 30, 2017

File No. 333-215231

Dear Ms. Long:

This will acknowledge receipt of your letter of comment, dated February 13, 2017 (“letter of comment”), regarding Amendment No. 1 to the Form S-4 Registration Statement (File No. 333-215231) (the “Registration Statement”) filed with the Securities and Exchange Commission (“SEC”) by Tecogen Inc., a Delaware corporation (the “Company”), on January 30, 2017 (“Amendment No. 1”).  In response to the SEC staff’s comments on Amendment No. 1, Amendment No. 2 to the Company’s Registration Statement (“Amendment No. 2”) was transmitted for filing on the date hereof. Capitalized terms used but not defined herein shall have the meaning ascribed to them in Amendment No. 2.

Amendment No. 2 further amends the Company’s Registration Statement in response to the comments raised in the SEC Staff’s letter of comment.  Amendment No. 2 also reflects the execution of Amendment No. 1 to the Merger Agreement (the “Merger Agreement Amendment”), a copy of which is appended to Annex A in Amendment No. 2.  The Merger Agreement Amendment clarifies the vote and proposals required to be approved by Tecogen and ADGE stockholders as a condition to the closing of the Merger and provides for the assumption by Tecogen of outstanding ADGE warrants to purchase common stock in connection with the Merger.

For the Staff’s convenience, we have set forth below the Staff’s comments in bold italics followed by the Company’s response to aid in your review.  Page references in the Company’s responses are to the joint proxy statement/prospectus contained in Amendment No. 2.

Stock Ownership of Directors and Executive Officers of Tecogen, page 6

Stock Ownership of Directors and Executive Officers of ADGE, page 6

1.

 We note in response to comment 2 of our letter dated January 17, 2017, you have removed references to George Hatsopoulos. Given the initial disclosure about his share ownership and the reference to him in the opinion of your financial advisor, please disclose his affiliation with the company. In addition, if Mr. Hatsopoulos has interests in the merger that are different from other shareholders, as the opinion of the financial advisor suggests, please disclose those interests.

Securities and Exchange Commission

March 24, 2017

Page 2

In response to the Staff’s comment, all references to Mr. George Hatsopoulos in this section were deleted from Amendment No. 1 and, other than the beneficial ownership tables, from Amendment No. 2 for the following reasons:

Mr. George Hatsopoulos is solely a shareholder of the Company.  He ceased to be a director of the Company on June 27, 2014 and is not otherwise affiliated with the Company.

Moreover, based solely upon the Company’s review of Mr. Hatsopoulos’ Schedule 13G/A filed with the SEC on December 12, 2016, he beneficially owns only approximately 6.79% of the Company’s common stock and, in view of having filed such disclosure on a Schedule 13G, the Company believes he is holding such shares solely for investment purposes.  Accordingly, the Company does not believe that Mr. George Hatsopoulos has any interest in the merger that is different from other shareholders.   Furthermore, his ownership of shares of the Company post-merger will increase from approximately 6.79% to only 8.2% of the Company’s total issued and outstanding shares of common stock.

The SEC Staff has inquired about why the financial advisor to the ADGE special committee specifically stated in its fairness opinion that its opinion does not apply to Mr. George Hatsopoulos.  ADGE has been advised by the financial advisor that it is the practice of many financial advisors to exclude significant shareholders from the scope of their opinions even in circumstances where, as here, the significant shareholder will receive the same consideration as the remaining shareholders.

Interests of Tecogen’s Directors and Executive Officers in the Merger, page 6

Interests of ADGE’s Directors and Executive Officers in the Merger, page 6

2.

 We note in your response to comment 3 of our letter dated January 17, 2017 and we reissue our comment. Please disclose all material interest of director, officers, and affiliates and quantify the interests of directors, executive officers, and affiliates in the summary. You provided cross references, but you do not quantify the interests of directors and executive officers. Please revise this section to quantify these interests for each person. Please ensure that you cite the correct page number in your cross references.

The disclosure has been revised as requested. See "Summary - Interests of Tecogen Directors and Executive Officers in the Merger" at page 12, "Summary - Interests of ADGE Directors and Executive Officers in the Merger" at page 13, "The Merger - Interests of Tecogen Directors and Executive Officers in the Merger" at page 80, and "The Merger - Interests of ADGE Directors and Executive Officers in the Merger" at page 81.

3.

 Please disclose the overlapping roles of any of the directors or executive officers. Please also disclose what role the directors and executive officers will serve in the surviving company. We note your statement that only Charles Maxwell and Benjamin Locke have an interest in the Merger that is different from, or in addition to, the interests of an ordinary Tecogen stockholder. It appears that other directors and officers may have interests different from an ordinary Tecogen stockholder. Please revise or advise.

The disclosure has been revised as requested.  See "Summary - Interests of Tecogen Directors and Executive Officers in the Merger" at page 12, "Summary - Interests of ADGE Directors and Executive Officers in the Merger" at page 13, "The Merger - Relationships and Overlaps" at page 62, "The Merger - Interests of Tecogen Directors and Executive Officers in the Merger" at page 80,  "The Merger - Interests of ADGE Directors and Executive Officers in the Merger," at page 81, and "Information About ADGE - Management of ADGE" at page 123.

Unaudited Pro Forma Condensed Combined Financial Information, page 11

Note 4. Fair Value Estimate of Assets to be Acquired and Liabilities to be Assumed, page 18

4.

 We note your response to prior comment six. As requested, please expand your disclosures to more fully explain how the purchase price was determined. In this regard, we note the significant losses incurred by ADGE and the magnitude of unfavorable customer contracts.

Securities and Exchange Commission

March 24, 2017

Page 3

We have expanded the disclosures as requested.  Please see Notes 3 and 4 to the Unaudited Pro Forma Condensed Combined Financial Statements for expanded disclosure more fully explaining how the purchase price was determined as well as expanded qualitative description of the factors that make up the goodwill.

Note 5. Adjustments to Pro Forma Balance Sheet, page 18

5.

 In regard to the additional disclosures you provided in your response to prior comment ten, please address the following:

•

 More fully explain to us and disclose the actual terms of ADGE’s customer contracts, including pricing provisions. It is not clear to us if the pricing provisions of the existing customer contracts are fixed or variable. To the extent the pricing provisions are not fixed, it is not clear to us how you determined the difference between the contracts terms and current market conditions;

Please see Note 5(d) to the Unaudited Pro Forma Condensed Combined Financial Statements for an explanation of the more relevant actual contractual terms, including pricing provisions and an explanation of how the contractual terms in respect of the pricing provisions were determined to be off market. Please note that in our disclosures “market terms” are in respect of contract terms while “market conditions” is primarily in respect of local utility electric rates at a point in time.

•

 Your disclosures indicate the unfavorable contract liability you recorded includes estimated contract extensions. More fully explain to us and disclose when and how customer contracts can be extended. To the extent contract extensions are not solely within the customers’ discretion, explain to us how and why including estimated extensions in determining an unfavorable contract liability is appropriate;

We have amended the disclosure in Note 5(d) to the Unaudited Pro Forma Condensed Combined Financial Statements omitting any reference to extensions of time beyond the initial contract term. That reference was in error as no extensions of time beyond the initial contract term were included in the actual calculations. While extensions of time beyond the initial contract term have historically occurred under the vast majority of contracts, it has been by mutual agreement between the parties to the contracts as is the contractual provision in respect of extensions. We do not believe an obligation to perform exists unless and until both parties to the contract have mutually agreed to extending the contract. In the absence of a current obligation to perform there is no basis for recognition for accounting purposes.

•

 More fully explain to us and disclose how you determined the discount rate you used;

Please see Note 5(d) to the Unaudited Pro Forma Condensed Combined Financial Statements for an explanation of how the discount rate used was determined.

•

 Your disclosures indicate you assume a gross profit margin of 35% based on Tecogen’s historical gross profit margin; however it appears to us that Tecogen sells equipment and ADGE essentially sells energy. More fully explain to us how and why you determined assuming a 35% gross profit margin is appropriate; and

While Tecogen is not a seller of energy as is ADGE, Tecogen does garner various financial metrics related to its customer’s expectations by virtue of its involvement in the construction of its customer’s cogeneration projects. That information was utilized to help determine the range of reasonableness in respect of the gross margin utilized which was based on certain financial metrics of US investor owned electrical utilities which are ADGE’s primary competitors. We have revised the disclosure in Note 5(d) to the Unaudited Pro Forma Condensed Combined Financial Statements to more fully describe how and why the gross margin percentage was determined.

•

 More fully explain to us and disclose how you determined contracts with favorable terms and contracts with unfavorable terms and why offsetting such contracts is appropriate.

Please see Note 5(d) to the Unaudited Pro Forma Condensed Combined Financial Statements for an explanation of how contracts with favorable terms and how contracts with unfavorable terms were determined.

Securities and Exchange Commission

March 24, 2017

Page 4

Upon further review, we have amended the filing to reflect the fair value assigned to contracts with terms which are considered to be favorable to market as intangible assets and to reflect the fair value assigned to contracts with terms which are considered to be unfavorable to market as an unfavorable contract liability thereby eliminating any offsetting.

Background, page 37

6.

 In response to comment 15 of our letter dated January 17, 2017, you stated that you added additional detail to the discussion. It doesn’t appear that those details were reflected in your amendment. We reissue our comment. Please revise this section to describe in sufficient detail who initiated contact among the parties, identify all parties present at the meetings, explain the material issues discussed, and the positions taken by those involved in each meeting.

The disclosure has been revised as requested.  See "The Merger - Background of the Merger," beginning at page 57.

Material U.S. Federal Income Tax Consequences of the Merger, page 60

7.

 In light of the short form tax opinion filed as exhibit 8 to your registration statement, please revise this section to clearly identify each material tax consequence, set forth the opinion of counsel as to each identified tax item; and set forth the basis for the opinion. If you are unable to opine on a material tax consequence, the opinion should state this fact clearly, provide the reason for your inability to opine on a material tax consequence (for example, the facts are currently unknown or the law is unclear); and discuss the possible alternatives and risks to investors of that tax consequence. Please see Staff Legal Bulletin 19 for guidance.

The disclosure has been revised as requested.  See "Material U.S. Federal Income Tax Consequences of the Merger," at page 93.

Where you can find more information; Incorporation by Reference, page 70

8.

 We note your response to comment 18 of our letter dated January 17, 2017 that both companies are S-3 eligible and therefore eligible to incorporate by reference; however, it appears that the aggregate market value of shares held by non-affiliates is not at least $75 million. Please provide your underlying analysis of eligibility for each company. Please note that if you are not eligible to incorporate by reference, then you will need to provide updated Executive Compensation information for the most recent fiscal year end required by Item 18(a)(7)(ii) of Form S-4.

Amendment No. 2 has been revised to include, rather than incorporate by reference, the required disclosures relating to Tecogen and ADGE throughout as requested.

Exhibit 23.5: Opinion of Cassel Salpeter & Co., LLC

9.

 We note the revision to this opinion now provide a consent that is limited to Amendment 1 to the S-4. Given that it appears another amendment may be necessary, please update this opinion or remove the limitation so that the consent applies to the S-4, as amended.

Exhibit 23.5 has been revised as requested and included as an exhibit to Amendment No. 2.

*    *    *

Securities and Exchange Commission

March 24, 2017

Page 5

   If you have any question regarding the foregoing, please feel free to call the undersigned at (781) 466-6400.

Sincerely,

TECOGEN INC.

By:    David A. Garrison

David Garrison, Chief Financial Officer

CC:    Kate McHale, Staff Attorney

Dale Welcome, Staff Accountant

Anne McConnell, Staff Accountant

February 13, 2017

Mr. John N. Hatsopoulos
Co-Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
Amendment No. 1 to Registration Statement on Form S -4
Filed January 30, 2017
  File No. 333-215231

Dear Mr. Hatsopoulos :

We have reviewed your amended registration statement  and have the following
comments.  In some of our comments, we may ask you to provide us with information so we
may better understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  If you do not believe our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.

After reviewin g any amendment to your registration statement and the information you
provide in response to these  comments, we may have  additional comments.   Unless we note
otherwise, our references to prior comments are to comments in our January 17, 2017 letter.

Stock Ownership of Directors and Executive Officers of Tecogen, page 6
Stock Ownership of Directors and Executive Officers of ADGE, page 6

1. We note in response to comment 2 of our letter dated January 17, 2017, you have
removed references to George Hatsopoulos .   Given the initial disclosure about his share
ownership and the reference to him in the opinion of your financial advisor, please
disclose his affiliation with the company.  In addition, if Mr. Hatsopoulos has interests in
the merger that are different from other shareholders, as the opinion of the financial
advisor suggests, please disclose those interests.

John N. Hatsopoulos
Tecogen, Inc.
February 13, 2017
Page 2

 Interests of Tecogen’s Directors and Executive Officers in the Merger, page 6
Interests of ADGE’s Directors and Executive Officers in the Merg er, page 6

2. We note in your response to comment 3 of our letter dated January 17, 2017 and we
reissue our comment.  Please disclose all material interest of director, officers, and
affiliates and quantify the interests of directors, executive officers, and  affiliates in the
summary.  You provided cross references, but you do not quantify the interests of
directors and executive officers.  Please revise this section to quantify these interests for
each person. Please ensure that you cite the correct page num ber in your cross references.

3. Please disclose the overlapping roles of any of the directors or executive officers. Please
also disclose what role the directors and executive officers will serve in the surviving
company. We note your statement that only Ch arles Maxwell and Benjamin Locke have
an interest in the Merger that is different from, or in addition to, the interests of an
ordinary Tecogen stockholder.  It appears that other directors and officers may have
interests different from an ordinary Tecogen  stockholder.  Please revise or advise.

Unaudited Pro Forma Condensed Combined Financial Information, page 11

Note 4. Fair Value Estimate of Assets to be Acquired and Liabilities to be Assumed, page 18

4. We note your response to prior comment six.  As requested, please expand your
disclosures to more fully explain how the purchase price was determined.  In this regard,
we note the significant losses incurred by ADGE and the magnitude of unfavorable
customer contracts.

Note 5.  Adjustments to Pro Forma Balance Sheet, page 18

5. In regard to the additional disclosures you provided in your response to prior comment
ten, please address the following:
 More fully explain to us and disclose the actual terms of ADGE’s customer contracts,
including pricing provisions.  It is not clear to us if the pricing provisions of the
existing customer contracts are fixed or variable.  To the extent the pricing provisions
are not fixed, it is not clear to us how you determined the difference between t he
contracts terms and current market conditions;
 Your disclosures indicate the unfavorable contract liability you recorded includes
estimated contract extensions.  More fully explain to us and disclose when and how
customer contracts can be extended.  To the extent contract extensions are not solely
within the customers’ discretion, explain to us how and why including estimated
extensions in determining an unfavorable contract liability is appropriate;
 More fully explain to us and disclose how you determin ed the discount rate you used;
 Your disclosures indicate you assume a gross profit margin of 35% based on
Tecogen’s historical gross profit margin; however it appears to us that Tecogen sells
equipment and ADGE essentially sells energy.  More fully explai n to us how and why
you determined assuming a 35% gross profit margin is appropriate; and

John N. Hatsopoulos
Tecogen, Inc.
February 13, 2017
Page 3

  More fully explain to us and disclose how you determined contracts with favorable
terms and contracts with unfavorable terms and why offsetting such contracts is
appropriate.

Background, page 37

6. In response to comment 15 of our letter dated January 17, 2017, you stated that you
added additional detail to the discussion. It doesn’t appear that those details were
reflected in your amendment.  We reissue our comment.  P lease revise this section to
describe in sufficient detail who initiated contact among the parties, identify all parties
present at the meetings, explain the material issues discussed, and the positions taken by
those involved in each meeting.

Material U .S. Federal Income Tax Consequences of the Merger, page 60

7. In light of the short form tax opinion filed as exhibit 8 to your registration statement,
please revise this section to clearly identify each material tax consequence, set forth the
opinion of cou nsel as to each identified tax item; and set forth the basis for the opinion.
If you are unable to opine on a material tax consequence, the opinion should state this
fact clearly, provide the reason for your inability to opine on a material tax consequen ce
(for example, the facts are currently unknown or the law is unclear); and discuss the
possible alternatives and risks to investors of that tax consequence.  Please see Staff
Legal Bulletin 19 for guidance.

Where you can find more information; Incorpor ation by Reference, page 70

8. We note your response to comment 18 of our letter dated January 17, 2017 that both
companies are S -3 eligible and therefore eligible to incorporate by reference; however, it
appears that the aggregate market value of shares held by non -affiliates is not at least $75
million.  Please provide your underlying analysis of eligibility for each company. Please
note that if you are not eligible to incorporate by reference, then you will need to provide
updated Executive Compensation  information for the most recent fiscal year end required
by Item 18(a)(7)(ii) of Form S -4.

Exhibit 23.5: Opinion of Cassel Salpeter & Co., LLC

9. We note the revision to this opinion now provide a consent that is limited to Amendment
1 to the S -4.  Given t hat it appears another amendment may be necessary, please update
this opinion or remove the limitation so that the consent applies to the S -4, as amended.

We remind you that the company and its management are responsible for the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action or absence of
action by the staff.

John N. Hatsopoulos
Tecogen, Inc.
February 13, 2017
Page 4

 Refer to Rules 460 and 461 regarding requests for acceleration .  Please allow adequate
time for us to review any amendment prior to the requested effecti ve date of the registration
statement.

You may contact Dale Welcome, Staff Accou ntant, at (202) 551 -3865,  or Anne
McConnell, Staff Accountant at (202) 551 -3709  if you have questions regarding comments on
the financial statements and re lated matters.  Please contact Kate McHale, Staff Attorney,  at
(202) 551 -3464  or me at (202) 551 - 3754 with any other questions.

Sincerely,

/s/ Asia Timmons -Pierce, for

Pamela A. Long
Assistant Director
Office of Manufacturing and
Construction

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January 27, 2017

Via EDGAR

Pamela Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc.

Registration Statement on Form S-4

Filed on December 21, 2016

File No. 333-215231

Dear Ms. Long:

The purpose of this letter is to respond to your letter of January 17, 2017 regarding the above registration statement. For your convenience, your original comments appear in italics, followed by our response.  We are concurrently filing on EDGAR Amendment No. 1 to the Form S-4.  Page references in our response are to Amendment No. 1.

General

1.The tax consequences of the transaction appear to be material under Item 601(b)(8) of Regulation S-K. In this regard, we note that you intend for the merger to qualify as a “reorganization” within the meaning of Section 368(a) of the Internal Revenue Code. Please provide a tax opinion supporting your conclusion that the merger will be tax free. Please refer to Staff Legal Bulletin No. 19, which is available on our website.

A tax opinion from our counsel, Sullivan & Worcester, LLP, has been filed as an exhibit to Amendment No. 1.

Stock Ownership of Directors and Executive Officers of Tecogen, page 6

Stock Ownership of Directors and Executive Officers of ADGE, page 6

2.The disclosure in these sections does not seem to reconcile with the disclosure on page 39. Please revise. In addition, please include the stock ownership of Tecogen after the merger by directors, officers, and affiliates.

Reconciliatory disclosure has been added to pages 11, 45, and 62. The requested table has been added to page 62.

Interests of Tecogen’s Directors and Executive Officers in the Merger, page 6

Interests of ADGE’s Directors and Executive Officers in the Merger, page 6

3.Please disclose all material interests of directors, executive officers, and affiliates and quantify the interests of directors, executive officers, and affiliates in the summary. Please also revise pages 26 and 38 as appropriate.

Certain officers and directors of both ADGE and Tecogen have interests in the Merger in addition to, or different from ordinary ADGE and Tecogen shareholders because they own ADGE common stock options that are subject to adjustment upon the closing of the Merger. For a detailed explanation of these potentially material interests, please see pages 11, 45 and 62.

Summary Unaudited Pro Forma Condensed Combined Financial Information, page 10

4.We note that the amounts presented under pro forma condensed combined balance sheet data as of September 30, 2016 on page 10 do not agree to corresponding amounts in the pro forma condensed combined balance sheet on page 13. Please clarify or revise as appropriate.

The summary unaudited pro forma condensed financial information has been revised on page 18.

Unaudited Pro Forma Condensed Combined Financial Information, page 11

Note 2. Basis of Pro Forma Presentation, page 16

5.In the fourth paragraph, you state that the pro forma financial statements are “based upon an estimated preliminary consideration of approximately $19.5 million”. However, notes 3 and 4 appear to estimate the preliminary consideration as $17.9 million. Please clarify or revise as appropriate.

The first paragraph on page 22 has been revised to reflect the appropriate amount.

Note 4. Fair Value Estimate of Assets to be Acquired and Liabilities to be Assumed, page 18

6.Since the acquisition will result in a considerable amount of goodwill relative to the purchase price, please provide a qualitative description of the factors that make up the goodwill to be recognized similar to the disclosures required by ASC 805-30-50-1(a). Please also expand your disclosures to more fully explain how the purchase price was determined. In this regard, we note the significant losses incurred by ADGE and the magnitude of unfavorable contracts.

The requested explanation and disclosure has been added to Note 4 on page 23.

Note 5. Adjustments to the Pro Forma Balance Sheet, page 18

Note 6. Adjustments to the Pro Forma Income Statements, page 20

7.Refer to footnote 5(b). Please more fully explain and disclose how you determined that the carrying value of ADGE’s inventory will be required to be written-down over 40% to record it at fair value. Please also more fully explain and disclose how and why ADGE determined the carrying value of inventory in its historical statements was not impaired at September 30, 2016.

The requested explanation and disclosure has been added to footnote 5(b) on page 23.

8.Refer to footnote 5(c). Please more fully explain and disclose how you determined that the carrying value of ADGE’s property, plant and equipment will be required to be written-down approximately 8% to record it at fair value. Please also more fully explain and disclose how and why ADGE determined the carrying value of property, plant and equipment in its historical statements was not impaired at September 30, 2016.

The requested explanation and disclosure has been added to footnote 5(c) on pages 23-24.

9.Refer to footnote 5(d). Please more fully explain and disclose how you determined the fair value of the liability related to ADGE’s guarantee of certain outstanding obligations of former subsidiaries and quantify the total amount of the all the obligations that are guaranteed. Please also disclose the specific nature of the estimated merger-related costs of $500,000.

The requested explanation and disclosure has been added to footnote 5(d) on page 24.

10.Refer to footnotes 5(e) and 6(b). Please expand your disclosures to describe the events and circumstances that resulted in ADGE’s contractual arrangements having unfavorable terms for most contracts, including the current terms of the contracts. Please also expand your disclosures to explain how you determined the fair value of the unfavorable contracts, including the significant assumptions you used.

The requested disclosure and explanation have been added to footnote 5(e) on pages 24-25.

11.Refer to footnote 5(h). Please more fully explain and disclose how you determined the fair value of the non-controlling interest at September 30, 2016.

Please refer to footnote 5(h) on page 26, Adjustments to the Pro Forma Balance Sheet, for a revised explanation of the pro forma adjustment in respect of the noncontrolling interest, which now more fully explains how the fair value of the noncontrolling interest was determined at September 30, 2016.

Please also note that amount of the adjustment required to arrive at an estimate of the fair value of the noncontrolling interest has been revised in the amended filing to correct for a data error and to allocate goodwill to the noncontrolling interest based on the results of the discounted cash flow analysis explained in footnote 5(h).

12.Refer to footnote 6(b). Based on the amount of the fair value adjustment to net property, please clarify how the related decreases in depreciation expense were determined.

The requested clarification has been added to footnote 6(b) on page 26.

Note 8. Exchange Transactions, page 21

13.Please more fully disclose how you calculated the amounts of historical interest expense associated with the convertible indebtedness that you eliminated from the pro forma statements of operations for each period presented.

The requested additional disclosure has been added to Note 8, Exchange Transactions, at page 27.

Comparative Tecogen and ADGE Market Price and Distribution Information, page 23

ADGE Recent Closing Prices, page 24

14.Please present the per share market value of ADGE’s securities on an equivalent per share basis as required by Item 3(g) of Form S-4.

The requested data has been added to page 29.

The Merger, page 36

Background of the Merger, page 36

General

15.Please revise the discussion in this section to describe in sufficient detail who initiated contact among the parties, identify all parties present at the meetings, explain the material issues discussed, and the positions taken by those involved in each meeting.

We have added some additional detail to the discussions. The discussions, after they were initiated, were held in the customary manner albeit somewhat more informally and expeditiously because of the close relationship of the merging companies. In that regard, we note the following:

•

 The two companies historically were one company;

•

 The companies have overlapping management and have detailed knowledge of each other's business, including because Tecogen is the primary vendor of equipment for ADGE; and

•

 The principal offices of both companies are located in the same building.

Contact was not initiated in the manner of independent third party offers, as suggested by your comment. The prospect of merging the two related companies had been discussed by the respective Boards and management from time to time over the years. In early 2016, based on a more detailed analysis, both managements concluded that a combination should be explored more deeply. Managements separately studied the case for the merger, both concluded that synergies would be achieved by a combination; and both reported their findings to their respective Boards. (These "reasons for the merger" are discussed in detail in the registration statement.)

Similarly, the issues discussed and the positions taken by those involved in each meeting primarily were related to price. The committees and counsel for the committees negotiated the detailed terms of the merger agreement in an expedited manner. The negotiation of the terms of the merger agreement was simplified because, based on the advice of outside counsel, the merger agreement did not contain provisions that are the usual points of difference - i.e., there were no provisions for "deal protection" devices, such as no-shops, termination fees and voting agreements.

The key issue for the transaction, where the separate interests of the companies were not aligned, was the exchange ratio. That issue was handled in the conventional manner of arm's-length negotiations by the two committees described in reasonable detail in the registration statement. The committees were assiduous in representing their separate constituencies in back-and-forth negotiations to arrive at an exchange ratio. There were multiple rounds of back-and-forth negotiations between the committees on price and secondarily on the cash value per share of Tecogen common stock. That said, the process was relatively informal and concluded fairly quickly and was conducted primarily by conference calls.

We are aware of the typical multi-page discussion of the merger negotiations in S-4 registration statements. That is not possible or appropriate here. We have added additional detail in the registration statement in an attempt to comply with your comment, including some of the historical context described above. We believe, given the circumstances described above, that our discussion is fair disclosure to the shareholders of both companies.

16.Please revise to disclose the members of the original special committees, how the members were selected and the committee’s duties. Please elaborate on the reasons the original special committee disbanded.

The members of the American DG special committee did not change and are disclosed on page 42.

The original members of the Tecogen special committee were Earl Lewis and Dr. Joseph Aoun.

Both committees were selected by the respective Board of Directors of the two companies. The qualifications of the members that were taken into consideration were the outsider status of the prospective committee members and, if possible, specialized expertise in the business of the two companies. Both committees were briefed in detail initially via a memorandum prepared by outside counsel to both companies, later confirmed by a member of that firm in Board/committee meetings, and reinforced by advice from the independent legal counsel appointed by each committee. In short, the committees were advised (and they understood) that their obligation, in short, was to negotiate a transaction on price and terms as favorable as possible to the stockholders of their respective stockholder constituencies.

The replacement of the Tecogen committee was not based on a disagreement about merger price or terms or any other substantive issue. The committee was simply taking to long to make a recommendation. The merger process began in March 2016; and the Tecogen special committee was appointed by the Board of Directors on March 15, 2016. The committee's first actions included selecting independent counsel and independent investment bankers. The Tecogen committee had made little progress by June; for example, its engagement letter with its investment bank adviser was not signed until June 14, 2016. As time went on, the Tecogen Board became increasingly concerned that extended delays in the transaction would be harmful to both companies. Unfortunately, at the time these concerns became acute, both members of the Tecogen special committee were leaving imminently for extended overseas vacations. The Board then met and determined that it was in the corporation's best interest to expedite matters and appointed a new committee. Mr. Earl Lewis attended that meeting and expressed his support for the merger. The new committee retained the same financial advisors, appointed new counsel, and was able to benefit from the data assembled by the original committee. The new Tecogen committee authorized an offer to ADGE on September 14, 2016, approximately three weeks after its appointment.

We do not believe that any of the foregoing information is material to investors, and that disclosure may unnecessarily embarrass the original members of the the committee.

Additional Considerations, page 39

17.Please revise to quantify here the anticipated synergies and cost savings expected to be realized from the merger that the Tecogen board of directors considered.

The requested explanation and disclosure has been added to the Additional Considerations section on page 46.

Where you can find more information; Incorporation by reference, page 67

18.We note you have incorporated by reference Exchange Act reports for both Tecogen and ADGE; please provide your analysis as to how you determined your eligibility for incorporation by reference. In addition, we note that you have not incorporated the quarterly reports for the first two quarters of 2016, as required by Item 11(a)(2) of Form S-4. Please revise or provide your analysis as to how you concluded these reports were not required.

Tecogen is an S-3 eligible issuer. It is listed on NASDAQ, is timely in its Exchange Act filings and otherwise qualifies.

The list of incorporated documents has been corrected and updated.

Exhibit 23.4; Opinion of Scarsdale Equities LLC

19.Please revise the second to last paragraph to provide consent to the use and description of the opinion in the S-4.

The paragraph has been revised as requested and the revised opinion filed with Amendment No. 1.

Exhibit 23.5: Opinion of Cassel Salpeter & Co., LLC

20.Please revise to remove the limitation on who may use and rely upon your opinion. In addition, please include your consent to the opinion’s use and description in the S-4.

The limitation has been removed; a consent has been included, as requested; and the revised opinion filed with Amendment No. 1.

*    *   .*

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call our attorneys, Ed Miller (617) 398-0408 or Ben Armour (617) 338-2423 of Sullivan & Worcester LLP in Boston, if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ David A Garrison

By:    David A. Garrison

Chief Financial Officer

cc:      Kate McHale, Staff Attorney

Dale Welcome, Staff Accountan

Mail Stop 4631
January 17, 2017

Mr. John N. Hatsopoulos
Co-Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
Registration Statement on Form S -4
Filed December 21, 2016
  File No. 333-215231

Dear Mr. Hatsopoulos :

We have reviewed your registration statement  and have the following comments.  In
some of our comments, we may ask you to provide us with information so we may better
understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  If you do not believe our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.

After reviewin g any amendment to your registration statement and the information you
provide in response to these  comments, we may have  additional comments.

General

1. The tax consequences of the transaction appear to be material under Item 601(b)(8) of
Regulation S -K.  In this regard, we note that you intend for the merger to qualify as a
“reorganization” within the meaning of Section 368(a) of the Internal Revenue Code.
Please provide a tax opinion supporting your conclusion that the merger will be tax free.
Please  refer to Staff Legal Bulletin No. 19, which is available on our website.

Stock Ownership of Directors and Executive Officers of Tecogen, page 6
Stock Ownership of Directors and Executive Officers of ADGE, page 6

2. The disclosure in these sections does not  seem to reconcile with the disclosure on page
39.  Please revise.  In addition, please include the stock ownership of Tecogen after the
merger by directors, officers, and affiliates.

John N. Hatsopoulos
Tecogen, Inc.
January 17, 2017
Page 2

Interests of Tecogen’s Directors and Executive Officers in the Merger,  page 6
Interests of ADGE’s Directors and Executive Officers in the Merger, page 6

3. Please disclose all material interests of directors, executive officers, and affiliates and
quantify the interests of directors, executive officers, and affiliates in the s ummary.
Please also revise pages 26 and 38 as appropriate.

Summary Unaudited Pro Forma Condensed Combined Financial Information, page 10

4. We note that the amounts presented under pro forma condensed combined balance sheet
data as of September 30, 2016 on page 10 do not agree to corresponding amounts in the
pro forma condensed combined balance sheet on page 13.  Please clarify or revise as
appropriate.

Unaudited Pro Forma Condensed Combined Financial Information, page 11
Note 2. Basis of Pro Forma Presenta tion, page 16

5. In the fourth paragraph, you state that the pro forma financial statements are “based upon
an estimated preliminary consideration of approximately $19.5 million”.  However, notes
3 and 4 appear to estimate the preliminary consideration as $1 7.9 million.  Please clarify
or revise as appropriate.

Note 4. Fair Value Estimate of Assets to be Acquired and Liabilities to be Assumed, page 18

6. Since the acquisition will result in a considerable amount of goodwill relative to the
purchase price, plea se provide a qualitative description of the factors that make up the
goodwill to be recognized similar to the disclosures required by ASC 805 -30-50-1(a).
Please also expand your disclosures to more fully explain how the purchase price was
determined.  In this regard, we note the significant losses incurred by ADGE and the
magnitude of unfavorable contracts.

Note 5. Adjustments to the Pro Forma Balance Sheet, page 18
Note 6. Adjustments to the Pro Forma Income Statements, page 20

7. Refer to footnote 5(b).  Please more fully explain and disclose how you determined that
the carrying value of ADGE’s inventory will be required to be written -down over 40% to
record it at fair value.  Please also more fully explain and disclose how and why ADGE
determined the carr ying value of inventory in its historical statements was not impaired at
September 30, 2016.

8. Refer to footnote 5(c).  Please more fully explain and disclose how you determined that
the carrying value of ADGE’s property, plant and equipment will be require d to be
written -down approximately 8% to record it at fair value.  Please also more fully explain

John N. Hatsopoulos
Tecogen, Inc.
January 17, 2017
Page 3

 and disclose how and why ADGE determined the carrying value of property, plant and
equipment in its historical statements was not impaired at September 30, 20 16.
9. Refer to footnote 5(d).  Please more fully explain and disclose how you determined the
fair value of the liability related to ADGE’s guarantee of certain outstanding obligations
of former subsidiaries and quantify the total amount of the all the obliga tions that are
guaranteed.  Please also disclose the specific nature of the estimated merger -related costs
of $500,000.

10. Refer to footnotes 5(e) and 6(b).  Please expand your disclosures to describe the events
and circumstances that resulted in ADGE’s co ntractual arrangements having unfavorable
terms for most contracts, including the current terms of the contracts.  Please also expand
your disclosures to explain how you determined the fair value of the unfavorable
contracts, including the significant assu mptions you used.

11. Refer to footnote 5(h).  Please more fully explain and disclose how you determined the
fair value of the non -controlling interest at September 30, 2016.

12. Refer to footnote 6(b).  Based on the amount of the fair value adjustment to net property,
please clarify how the related decreases in depreciation expense were determined.

Note 8. Exchange Transactions, page 21

13. Please more fully disclose how you calcul ated the amounts of historical interest expense
associated with the convertible indebtedness that you eliminated from the pro forma
statements of operations for each period presented.

Comparative Tecogen and ADGE Market Price and Distribution Information,  page 23
ADGE Recent Closing Prices, page 24

14. Please present the per share market value of ADGE’s securities on an equivalent per
share basis as required by Item 3(g) of Form S -4.

The Merger, page 36
Background of the Merger, page 36
General

15. Please revise the discussion in this section to describe in sufficient detail who initiated
contact among the parties, identify all parties present at the meetings, explain the material
issues discussed, and the positions taken by those involved in each meeting.

16. Please revise to disclose the members of the  original special committee s, how the
members were selected and the committee’s duties.  Please elaborate on the reasons the
original special committee disbanded.

John N. Hatsopoulos
Tecogen, Inc.
January 17, 2017
Page 4

Additional Considerations, page 39

17. Please revise  to quantify here the anticipated synergies and cost savings expected to be
realized from the merger that the  Tecogen board of directors considered.

Where you can find more information; Incorporation by reference, page 67

18. We note you have incorpora ted by reference Exchange Act reports for both Tecogen and
ADGE; please provide your analysis as to how you determined your eligibility for
incorporation by reference.  In addition, we note that you have not incorporated the
quarterly reports for the first  two quarters of 2016, as required by Item 11(a)(2) of Form
S-4.  Please revise or provide your analysis as to how you concluded these reports were
not required.

Exhibit 23.4; Opinion of Scarsdale Equities LLC

19. Please revise the second to last paragraph to provide consent to the use and description of
the opinion in the S -4.

Exhibit 23.5: Opinion of Cassel Salpeter & Co., LLC

20. Please revise to remove the limitation on who may use and rely upon your opinion.  In
addition, please include your consent to the opinion’s use and description in the S -4.

We remind you that the company and its management are responsible for the accuracy
and adequacy of their disclosures, notwithstanding any review, comments, action or absence of
action by the staff.

Refer to Rules 460 and 461 regarding requests for  acceleration .  Please allow adequate
time for us to review any amendment prior to the requested effective date of the registration
statement.

John N. Hatsopoulos
Tecogen, Inc.
January 17, 2017
Page 5

 You may contact Dale Welcome, Staff Accou ntant, at (202) 551 -3865, or Anne
McConnell, Staff Accountant , at (202) 551 -3709  if you have questions regarding comments on
the financial statements and re lated matters.  Please contact Kate McHale, Staff Attorney,  at
(202) 551 -3464  or me at (202) 551 -3754 with any other questions.

Sincerely,

/s/ Asia Timmons -Pierce, for

Pamela A. Long
Assistant Director
Office of Manufacturing and
Construction

CORRESP
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		Document

July 14, 2016

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:    Tecogen Inc. (the "Company")

Registration Statement on Form S-3

Originally Filed July 7, 2015

File No. 333-212433

Dear Staff:

 In accordance with Rule 461 under the Securities Act of 1933, as amended, the undersigned respectfully requests that the effective date for the Registration Statement referred to above be accelerated so that it will be declared effective at 4:00 PM on July 18, 2016 or as soon thereafter as is practicable.

The Company hereby authorizes Benjamin J. Armour, of Sullivan & Worcester LLP, to orally modify or withdraw this request for acceleration.

The Company hereby acknowledges that:

•

 should the Commission or the staff, acting pursuant to delegated authority, declare the filing effective, it does not foreclose the Commission from taking any action with respect to the filing;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the filing effective, does not relieve the Company from its full responsibility for the adequacy and accuracy of the disclosure in the filing; and

•

 the Company may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

We request that we be notified of such effectiveness by a telephone call to Mr. Armour at (617) 338-2423. We also respectfully request that a copy of the written order from the Commission verifying the effective time and date of such Registration Statement be sent to Sullivan & Worcester LLP, attention: Benjamin J. Armour, via facsimile at (617) 338-2880.

Very truly yours,

Tecogen Inc.

By: /s/ David A. Garrison

David A. Garrison

Chief Financial Officer

Mail Stop 4631

July 12 , 2016

Via E -mail
Michael Rispin
Tecogen  Inc.
45 First Avenue
Waltham, Massachusetts 02451

Re: Tecogen  Inc.
  Registration Statement on Form S-3
Filed  July 7, 2016
  File No.  333-212433

Dear  Mr. Rispin :

This is to advise you that we have not  reviewed and will not review your registration
statement .

We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Act of 193 3 and
all applicable Securities  Act rules require.   Since the company and its management are  in
possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

In the event you request acceleration of t he effective date of the pending regist ration
statement , please provide  a written statement from the company acknowledging that:

 should the Commission or the staff, acting pursuant to delegated authority, declare the
filing effective, it does not foreclos e the Commission from taking any action with respect
to the filing;

 the action of the Commission or the staff, acting pursuant to delegated authority, in
declaring the filing effective, does not relieve the company from its full responsibility for
the ad equacy and accuracy of the disclosure in the filing; and

 the company may not assert staff comments and the declaration of effectiveness as a
defense in any proceeding initiated by the Commission or any person under the federal
securities laws of the Unit ed States.

Michael Rispin
Tecogen  Inc.
July 12 , 2016
Page 2

 Please refer to Rules 460 and 461 regarding requests for  acceleration .  We will consider a
written request for acceleration of the effective date of the registration statement as confirmation
of the fact that those requesting acceleration are a ware of their respective responsibilities under
the Securities Act of 1933 and the Securities Exchange Act of 1934 as they relate to the proposed
public offering of the registered securities .

Please  contact Chris Ronne, Staff Attorney, at (202) 551 -6156  or me at (202) 551 -3397
with any questions.

Sincerely,

 /s/ Jay Ingram

 Jay Ingram
Legal Branch Chief
Office of Manufacturing and
Construction

Cc:  Edwin Miller, Esq.
 Benjamin Armour, Esq.
 William Hanson, Esq.

CORRESP
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		CORRESP

September 30, 2015

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

   Attention:     Ms. Pamela Long, Assistant Director

Ms. Asia Timmons-Pierce, Staff Attorney

Re:    Tecogen Inc.

Registration Statement on Form S-3

Originally Filed June 22, 2015

Amendment No. 3 Filed September 29, 2015

File No. 333-205147

Dear Staff:

 In accordance with Rule 461 under the Securities Act of 1933, as amended, the undersigned respectfully requests that the effective date for the Registration Statement referred to above be accelerated so that it will be declared effective at 4:30 PM today, September 30, 2015 or as soon thereafter as is practicable.

The Company hereby acknowledges that:

•

 should the Commission or the staff, acting pursuant to delegated authority, declare the filing effective, it does not foreclose the Commission from taking any action with respect to the filing;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the filing effective, does not relieve the Company from its full responsibility for the adequacy and accuracy of the disclosure in the filing; and

•

 the Company may not assert this action as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

Very truly yours,

Tecogen Inc.

By: /s/ David A. Garrison

David A. Garrison

Chief Financial Officer

Mail Stop 4631

September 30, 2015

Via E -mail
Michael S. Rispin
Corporate & Securities Counsel
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
Form 10 -K
Filed March 25, 2015
File No. 001-36103

Dear Mr. Rispin :

We have completed our review of your filing .  We remind you that our comments or
changes to disclosure in response to our comments do not foreclose the Commission from taking
any action with respect to the com pany or the filing and the company may not assert staff
comments as a defense in any proceeding initiated by the Commission or any person under the
federal securities laws of the United States.  We urge all persons who are responsible for the
accuracy and adequacy of the disclosure in the filing to be certain that the filing includes the
information the Securities Exchange Act of 1934 and all applicable rules require.

Sincerely,

 /s/ Pamela Long

Pamela Long
Assistant Director
Office of Manufacturing and
Construction

cc: Benjamin Armou r (via email )
      Sullivan & Worcester LLP

CORRESP
1
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		CORRESP

September 28, 2015

Via EDGAR

Pamela Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the "Company")

Amendment No. 2 to Registration Statement on Form S-3 originally filed June 22, 2015 (the "Registration Statement")

File No. 333-205147

Dear Ms. Long:

The purpose of this letter is to: (1) Provide an additional response to your office's second comment in your letter to the Company dated September 14, 2015 regarding the Registration Statement; and (2) respond to your clarifications that were issued orally to the Company on Friday September 25, 2015.  For your convenience, your written comment appears below in bold text, followed by our response.

Please amend your filing to provide a consent from McGladrey LLP that properly identifies the date of their report contained in your 2014 Form 10-K, which you incorporate by reference into your Form S-3.

The Company kindly requests that the Commission allow the Company to let the Registration Statement become effective despite the date of McGladrey LLP's ("McGladrey") consent to the Registration Statement (the "Consent") does not match the date of their audit report (the "Audit Report")  included in the Company's fiscal year 2014 Form 10-K (the "2014 10-K").  In support of this request, the Company takes the position that this is an immaterial inconsistency, and correcting this mistake would cause the Company undue hardship.

In support of the position that this is an immaterial inconsistency, the Company cites to the following facts:

1.

 This inconsistency is the result of a typographical error that occurred during the edgarization process of the 2014 10-K.  The Company acknowledges that the date of the Audit Report, as filed in EDGAR, is incorrect and does not match the date of the paper copy of the Audit Report provided by McGladrey.  The Company emphasizes that this inconsistency was due to an error in the edgarization process, that all other dates related to McGladrey's audit of the fiscal year 2013 financial statements contained in the 2014 10-K are correct, and that this inconsistency is generally without consequence.  To emphasize, the paper copy of the Audit Report provided by McGladrey to the Company was correctly dated March 31, 2015.

2.

 There is only a 7 day difference between the date in the Consent and the date of the Audit Report.

3.

 The general purpose of the Consent has already been accomplished.  This is evidenced where McGladrey has issued the Consent and this is proof that:  (a) McGladrey has been provided notice of the Company's intent to incorporate their Audit Report by reference into the Registration Statement; (b) McGladrey is willing to consent to the Company incorporating the Audit Report by reference into the Registration Statement; and (c) the McGladrey has carried out their duties in connection with issuing consents.

The Company takes the position that correcting the inconsistent date mentioned above would cause the Company undue hardship because correcting this inconsistency would force the Company to amend their 2014 10-K.  The cost of amending the 10-K would likely have a material affect on the Company finances because:  (1) The cost of amending the Company's 2014 10-K will be high relative to the Company's size and net income; (2) the Company has yet to obtain profitability; and (3) the Company's issuer status remains that of an emerging growth company and a smaller reporting company.  The Company has no means to correct the inconsistency other than amending its 2014 10-K because McGladrey has been unwilling to issue their Consent with any date other March 31, 2014 or deviate from the language of their standard consent.

For the reason's cited above, the Company kindly requests that the Commission allow the Company to let the Registration Statement become effective despite the date of McGladrey's Consent to the Registration Statement not matching the date of their Audit Report  included in the 2014 10-K.

*     *    *

The Company respectfully advises the Staff that the Company acknowledges that:

•

 the Company is responsible for the adequacy and accuracy of the disclosure in the filing;

•

 Staff comments or changes to disclosure in response to Staff comments do not foreclose the Commission from taking any action with respect to the filing; and

•

 the Company may not assert Staff comments as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6403 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ David A Garrison

By:    David A. Garrison

Chief Financial Officer

cc:      Tracey McKoy, Staff Accountant

Jeanne Baker, Assistant Chief Accountant

Asia Timmons-Pierce, Staff Attorney

CORRESP
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		CORRESP

September 23, 2015

Via EDGAR

Pamela Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the "Company")

Amendment No. 1 to Registration Statement on Form S-3 originally filed June 22, 2015 (the "Registration Statement")

File No. 333-205147

Dear Ms. Long:

The purpose of this letter is to respond to your office's comment letter dated September 14, 2015 regarding the Company's first amendment to the Registration Statement. For your convenience, your comments appear below in bold text, followed by our response. As discussed over the phone today, September 23, 2015, in addition to filing this correspondence the Company shall simultaneously refile Part II of the Registration Statement to include the corrections outlined below.

1. Please provide the requested Tandy representations in your next response letter.

Please note that these representations have been included in this correspondence.

2. Please amend your filing to provide a consent from McGladrey LLP that properly identifies the date of their report contained in your 2014 Form 10-K, which you incorporate by reference into your Form S-3.

In response to your comment letter and to our discussion today, the Company shall in its second Amendment to the Registration Statement provide a consent from McGladrey LLP that properly identifies the date of McGladrey LLP's printed original report that was provided to the Company in connection with the Company's 2014 Form 10-K.

*     *    *

The Company respectfully advises the Staff that the Company acknowledges that:

•

 the Company is responsible for the adequacy and accuracy of the disclosure in the filing;

•

 Staff comments or changes to disclosure in response to Staff comments do not foreclose the Commission from taking any action with respect to the filing; and

•

 the Company may not assert Staff comments as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6403 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ David A Garrison

By:    David A. Garrison

Chief Financial Officer

cc:      Tracey McKoy, Staff Accountant

Jeanne Baker, Assistant Chief Accountant

Asia Timmons-Pierce, Staff Attorney

Mail Stop 4631

September 14, 2015

Via E -mail
Michael S. Rispin
Corporate & Securities Counsel
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
Amendment No. 1  to Re gistration Statement on Form S -3
Filed September 1, 2015
  File No. 333-205147

Dear Mr. Rispin :

We have reviewed your amended registration statement  and have the following
comments .  In some of our comments, we may ask you to provide us with information so we
may better understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  If you do not believe our comments apply to your facts and
circumstances or do not bel ieve an amendment is appropriate, please tell us why in your
response.

After reviewing any amendment to your registration statement and the information you
provide in response to these  comments, we may have  additional comments.   Unless  we note
otherwise , our references to prior comments are to comments in our July 16, 2015 letter .

General

1. Please provide the req uested Tandy representations in your next response letter.

Auditor’s Consent

2. Please amend your filing to provide a consent from McGladrey LLP that properly identifies
the date of their report contained in your 2014 Form 10 -K, which you incorporate by
reference into your Form S -3.

Michael S. Rispin
Tecogen Inc.
September 14, 2015
Page 2

 You may contact Tracey McKoy, Staff Accountant,  at (202) 551 -3772 or Jeanne Baker,
Assistant Chief Accountant, at (202) 551 -3691 if you have questions regarding comments on the
financial statements and re lated matters.  Please contact Asia Timmons -Pierce, Staff Attorney,  at
(202) 551 -3754 or me at  (202) 551 -3765 with any other questions.

Sincerely,

 /s/ Pamela Long

Pamela Long
Assistant Director
Office of Manufacturing and
Construction

cc: Benjamin Armou r (via email )
      Sullivan & Worcester LLP

July 16, 2015

Via E -mail
Michael S. Rispin
Corporate & Securities Counsel
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Registration Statement on Form S-3
Filed  June 22, 2015
  File No.  333-205147

Dear Mr. Rispin :

We have limited our review of your registration statement to those issues we have
addressed in our comments.  In  some of our comments, we may ask you to provide us with
information so we may better understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  If you do not believe our com ments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.

After reviewing any amendment to your registration statement and the information you
provide in response to these  comments, w e may have  additional comments.

Form S -3

Auditor’s Consent

1. We have read your response to comments one and two from our oral comments issued July 9,
2015.  Item 12(a)(1) of Form S -3 requires you to specifically incorporate by reference your
latest annu al report on Form 10 -K that contains financial statements for your latest fiscal
year.  As required by Rule 8 -02 of Regulation S -X, your Form 10 -K for the year ended
December 31, 2014 includes audited balance sheets as of December 31, 2014 and 2013 and
audited statements of income, cash flows and changes in stockholders’ equity for each of the
years then ended.  You therefore must provide a consent for the use of McGladrey LLC’s
report dated March 24, 2014.  Please also refer to your reliance on this report  in the Experts
section on page six.

Michael S. Rispin
Tecogen Inc.
July 16, 2015
Page 2

 We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Act of 193 3 and
all applicable Securities  Act rules require.   Since the company and its management are in
possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

Notwithstanding our comments, in the event you request acceleration of the effective date
of the pending registration statement , please provide a written statement from the company
acknowledging that:

 should the Commission or the staff, acting pursuant to delegated authority, declare the
filing effective, it does not foreclose the Commission from taking any action with respect
to the filing;

 the action of the Commission or the staff, acting pursuant to delegated authority, in
declaring the filing effective, does not relieve the company from its full responsibility for
the adequacy and accuracy of the disclosure in the filing; and

 the company  may not assert staff comments and the declaration of effectiveness as a
defense in any proceeding initiated by the Commission or any person under the federal
securities laws of the United States.

Please refer to Rules 460 and 461 regarding requests for  acceleration .  We will consider a
written request for acceleration of the effective date of the registration statement as confirmation
of the fact that those requesting acceleration are aware of their respective responsibilities under
the Securities Act of 1933 and the Securities Exchange Act of 1934 as they relate to the proposed
public offering of the securities specified in the above registration statement.  Please allow
adequate time  for us to review any amendment prior to the requested effective date of  the
registration statement.

You may contact Tracey McKoy, Staff Accountant,  at (202) 551 -3772 or Jeanne Baker,
Assistant Chief Accountant, at (202) 551 -3691 if you have questions regarding comments on the
financial statements and re lated matters.  Please contact Asia Timmons -Pierce, Staff Attorney,  at
(202) 551 -3754 or me at  (202) 551 -3765 with any other questions.

Sincerely,

 /s/ Pamela Long

 Pamela Long
Assistant Director

Michael S. Rispin
Tecogen Inc.
July 16, 2015
Page 3

cc: Benjamin Armou r (via email )
      Sullivan & Worcester LLP

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		TGN-2015.07.13 Corres S-3 Comment Ltr

July 13, 2015

VIA EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, DC 20549

Re:    Tecogen, Inc.

Registration Statement on Form S-3

Filed June 22, 2015

File No. 333-205147

Dear Staff:

Tecogen Inc. (the "Company" or "TGEN") is submitting this letter in response to oral comments from the staff (the "Staff") of the Securities And Exchange Commission (the "Commission") received by phone on July 10, 2015 related to the Company's Registration Statement  referenced above (the "Registration Statement"). The numbered paragraphs below correspond to the Staff's comments to the Company. The text of the Staff's comments are in bold italics.

1.

 On page 6 of the Registration Statement under "Experts", please provide necessary disclosure concerning McGladrey LLP.  If you believe this disclosure is not necessary, please explain why.

The disclosure mentioned above concerning McGladrey LLP is not necessary because McGladrey LLP did not prepare or certify any portion of the Registration Statement, including any financial statements incorporated by reference. In general, item 10 of Form S-3 pursuant to item 509 of regulation S-K requires issuers to furnish information concerning experts that prepare or certify any part of the report at issue. Regarding the Registration Statement, McGladrey LLP did not prepare or certify any part of the Registration Statement because the Company did not incorporate by reference into the Registration Statement any financial statements that were audited by McGladrey LLP.  See Exhibit 23.2 to the Company's 2014 Annual Report filed with the Commission on form 10-K on December 31, 2014.  McGladrey audited the Company's financial Statements for the year ended December 31, 2013. Id. The Company did not incorporate those financial statements by reference into the Registration Statement. The Company did incorporate by reference into the Registration Statement the financial statements for the year ended December 31, 2014, however those financial statements were not audited by McGladrey LLP. See Exhibit 23.1 to the Company's 2014 Annual Report filed with the Commission on form 10-K on December 31, 2014.

The Company was not required to have McGladrey LLP prepare or certify any part of the Registration Statement because the Company was not required to incorporate by reference any financial statements audited by McGladrey LLP. For further detail, please see the answer to question two.

2.

 Please provide a consent from McGladrey LLP.  If you believe this consent is not necessary, please explain why.

A consent from McGladrey LLP is not necessary because the Company did not incorporate by reference into the Registration Statement any financial statements audited by McGladrey LLP. McGladrey LLP did not audit the Company's financial statements for the year ended December 31, 2014.  See Exhibit 23.2 to the Company's 2014 Annual report filed with the Commission on form 10-K on December 31, 2014.

The Company is not required to incorporate by reference audited financial statements for the fiscal year ended December 31, 2013 because item 12(a)(1) of Form S-3 requires the incorporation by reference of "financial statements for the registrants' latest fiscal year[.]" Please note that this instruction uses the singular form of "year". Pursuant to this instruction, the Company did not incorporate by reference its audited financial statements for the year ending December 31, 2013.

Thank you for taking the time to review this request.

Sincerely,

Tecogen Inc.

/s/ David A. Garrison

David A. Garrison

Chief Financial Officer

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		TGEN 2014 12 05 Corres - S-3 Accel Request 2

December 5, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

   Attention:     Kamyar Daneshvar, Staff Attorney

Re:    Tecogen Inc.

Registration Statement on Form S-3

Originally Filed October 28, 2014

Amendment No. 1 Filed November 26, 2014

Amendment No. 2 Filed December 4, 2014

File No. 333-199634

Dear Staff:

Tecogen Inc. hereby withdrawals its prior request.  Tecogen Inc. now requests acceleration of the effectiveness of the above-referenced Registration Statement pursuant to Rule 461 under the Securities Act of 1933, as amended (or the Securities Act), so that it may become effective on December 5, 2014, at 5:00 p.m., Eastern Time, or as soon thereafter as is practicable.

Pursuant to Rule 460 of the Act, please be advised that through the date hereof, the undersigned effected the The Registrant acknowledges that:

•

 should the Securities and Exchange Commission (or the Commission) or the staff, acting pursuant to delegated authority, declare the Registration Statement effective, it does not foreclose the Commission from taking any action with respect to the Registration Statement;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the Registration Statement effective, does not relieve the Registrant from its full responsibility for the adequacy and accuracy of the disclosure in the Registration Statement; and

•

 the Registrant may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

The Registrant understands that the Commission will consider this request for acceleration of the effective date of the Registration Statement as a confirmation of the fact that the Registrant is aware of its responsibilities under the Securities Act, as they relate to the proposed public offering of the securities specified in the Registration Statement.

Sincerely,

TECOGEN INC.

/s/ David A. Garrison

David A. Garrison

Chief Financial Officer

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		TGEN 2014 12 05 Corres - S-3 Accel Request

December 4, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

   Attention:     Kamyar Daneshvar, Staff Attorney

Re:    Tecogen Inc.

Registration Statement on Form S-3

Originally Filed October 28, 2014

Amendment No. 1 Filed November 26, 2014

Amendment No. 2 Filed December 4, 2014

File No. 333-199634

Dear Staff:

Tecogen Inc. hereby requests acceleration of the effectiveness of the above-referenced Registration Statement pursuant to Rule 461 under the Securities Act of 1933, as amended (or the Securities Act), so that it may become effective on December 9, 2014, at 4:30 p.m., Eastern Time, or as soon thereafter as is practicable.

Pursuant to Rule 460 of the Act, please be advised that through the date hereof, the undersigned effected the The Registrant acknowledges that:

•

 should the Securities and Exchange Commission (or the Commission) or the staff, acting pursuant to delegated authority, declare the Registration Statement effective, it does not foreclose the Commission from taking any action with respect to the Registration Statement;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the Registration Statement effective, does not relieve the Registrant from its full responsibility for the adequacy and accuracy of the disclosure in the Registration Statement; and

•

 the Registrant may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

The Registrant understands that the Commission will consider this request for acceleration of the effective date of the Registration Statement as a confirmation of the fact that the Registrant is aware of its responsibilities under the Securities Act, as they relate to the proposed public offering of the securities specified in the Registration Statement.

Sincerely,

TECOGEN INC.

/s/ David A. Garrison

David A. Garrison

Chief Financial Officer

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		TGN 2014 12 04 Corres - S-3 Comment Ltr

`

December 4, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

   Attention:     Jay Ingram, Legal Branch Chief

Kamyar Daneshvar, Staff Attorney

Re:    Tecogen Inc.

Registration Statement on Form S-3

Originally Filed October 28, 2014

Amendment No. 1 Filed November 26, 2014

File No. 333-199634

Dear Staff:

We are submitting this letter on behalf of Tecogen Inc (the “Company” or “TGEN”) in response to comments from the staff (the “Staff”) of the Securities and Exchange Commission (the “Commission”) received by electronic mail dated December 1, 2014 relating to the Company’s Amended Registration Statement on Form S-3 (File No. 333-199634) filed with the Commission on November 26, 2014 (“ Amended Registration Statement No. 1”). The numbered paragraphs below correspond to the numbered comments in the Staff’s letter and the Staff’s comments are presented in bold.

General

1.

 Please amend your filing to include currently-dated signatures and an updated auditor’s consent.

We have updated the signature dates. In order negate the necessity of an updated auditor's consent, we have deleted Part I. These change will be reflected in our amendment to Amended Registration Statement No 1. In addition, there have been no material changes in the Company's financial statements since October 28, 2014, the date that the original version of the aforementioned Form S-3 was filed.

*   *   *

In connection with responding to the Staff's comments, the Company hereby acknowledge and shall state in any future request for acceleration:

•

 should the Commission or the Staff, acting pursuant to delegated authority, declare the filing effective, it does not foreclose the Commission from taking any action with respect to the filing;

•

 the action of the Commission or the Staff, acting pursuant to delegated authority, in declaring the filing effective, does not relieve the company from its full responsibility for the adequacy and accuracy of the disclosure in the filing; and

•

 the Company may not assert Staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6403 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.Sincerely,

TECOGEN INC.

By: /s/ David A. Garrison

David A. Garrison

Chief Financial Officer

December 1 , 2014

Via E -mail
David A. Garrison
Chief Financial Officer, Treasurer and Secretary
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Amendment No. 1 to Registration Statement on Form S-3
Filed  November 26 , 2014
  File No.  333-199634

Dear Mr. Garrison :

We have reviewed your amended registration statement and have the following
comments.

General

1. Please amend your filing to include currently -dated signatures and an updated auditors’
consent .

Please contact Kamyar Daneshvar, Staff Attorney  at (202) 551 -3787  or me at (202) 551 -
3397 with any  questions.

Sincerely,

 /s/ Jay Ingram

Jay Ingram
Legal Branch Chief

cc: Edwin L. Miller ( via e -mail)
 Sullivan & Worcester LLP

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		TGN 2014 11 26 Corres - S-3 Comment Ltr

`

November 26, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

   Attention:     Jay Ingram, Legal Branch Chief

Kamyar Daneshvar, Staff Attorney

Re:    Tecogen Inc.

Registration Statement on Form S-3

Filed October 28, 2014

File No. 333-199634

Dear Staff:

We are submitting this letter on behalf of Tecogen Inc (the “Company” or “TGEN”) in response to comments from the staff (the “Staff”) of the Securities and Exchange Commission (the “Commission”) received by electronic mail dated November 4, 2014 relating to the Company’s Registration Statement on Form S-3 (File No. 333-199634) filed with the Commission on October 28, 2014 (the “Registration Statement”). The numbered paragraphs below correspond to the numbered comments in the Staff’s letter and the Staff’s comments are presented in bold.

Calculation of Registration Fee Table

1.

 We note your disclosure in note (1) that the registration statement covers "such an indeterminate amount of common stock (with accompanying purchase rights, if any) . . .” [and] such an indeterminate amount of warrants, representing rights to purchase common stock .... " [emphasis added]. It is unclear if you are registering the offering of rights as a separate security in the fee table. Please revise accordingly or explain why you do not believe this is appropriate. If you are registering the offering of rights, please have counsel file an updated legality opinion covering the rights. For guidance, please refer to Question 116.16 of the Compliance and Disclosure Interpretations on Securities Act Forms available on the Commission’s web site.

We have deleted the reference to representation rights. This change will be reflected in our amended S-3.

*   *   *

In connection with responding to the Staff's comments, the Company hereby acknowledge and shall state in any future request for acceleration:

•

 should the Commission or the Staff, acting pursuant to delegated authority, declare the filing effective, it does not foreclose the Commission from taking any action with respect to the filing;

•

 the action of the Commission or the Staff, acting pursuant to delegated authority, in declaring the filing effective, does not relieve the company from its full responsibility for the adequacy and accuracy of the disclosure in the filing; and

•

 the Company may not assert Staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6403 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.Sincerely,

TECOGEN INC.

By: /s/ David A. Garrison

David A. Garrison

Chief Financial Officer

November 4, 2014

Via E -mail
David A. Garrison
Chief Financial Officer, Treasurer and Secretary
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Registration Statement on Form S-3
Filed  October 28, 2014
  File No.  333-199634

Dear Mr. Garrison :

We have limited our review of your registration statement to those issues we have
addressed in our comments.  In  some of our comments, we may ask you to provide us with
information so we may better understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  Where you do not believe our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.

After reviewing any amendment to your registration statement and the information you
provide in response to these  comments , we may have  additional comments.

Calculation of Registration Fee Table

1. We note your disclosure in note (1) that the registration statement covers “such an
indeterminate amount of common stock ( with accompanying purchase rights , if any) . . .”
[and] s uch an indeterminate amount of warrants, representing rights to purchase  common
stock . . . .” [emphasis added].  It is unclear if you are registering the offering of rights as
a separate security in the fee table.  Please revise accordingly or explain why  you do not
believe this is appropriate.  If you are registering the offering of rights, please have
counsel file an updated legality opinion covering the rights.  For guidance, please refer to
Question 116.16 of the Compliance and Disclosure Interpretatio ns on Securities Act
Forms available on the Commission’s web site.

We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Act of 193 3 and
all applicable Securities  Act rules require.   Since the company and its management are in

David A. Garrison
Tecogen Inc.
November 4, 2014
Page 2

 possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

Notwithstanding our comments, in the event you request acceleration of the effective date
of the pending registration statement please provide a written statement from the company
acknowledging that:

 should the Commission or the staff, acting pursuant to delegated author ity, declare the
filing effective, it does not foreclose the Commission from taking any action with respect
to the filing;

 the action of the Commission or the staff, acting pursuant to delegated authority, in
declaring the filing effective, does not reli eve the company from its full responsibility for
the adequacy and accuracy of the disclosure in the filing; and

 the company may not assert staff comments and the declaration of effectiveness as a
defense in any proceeding initiated by the Commission or any person under the federal
securities laws of the United States.

Please refer to Rules 460 and 461 regarding requests for  acceleration .  We will consider a
written request for acceleration of the effective date of the registration statement as confirmat ion
of the fact that those requesting acceleration are aware of their respective responsibilities under
the Securities Act of 1933 and the Securities Exchange Act of 1934 as they relate to the proposed
public offering of the securities specified in the abo ve registration statement.  Please allow
adequate time  for us to review any amendment prior to the requested effective date of the
registration statement.

Please contact Kamyar Daneshvar, Staff Attorney  at (202) 551 -3787  or me at (202) 551 -
3397 with any questions.

Sincerely,

 /s/ Jay Ingram

Jay Ingram
Legal Branch Chief

cc: Edwin L. Miller ( via e -mail)
 Sullivan & Worcester LLP

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		TGN 2014 07 01 Corres - Accel Request S-1 Eff

July 1, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:    Tecogen Inc. Registration Statement on Form S-1 (or the Registration Statement) No. 333-193791

Ladies and Gentlemen:

Tecogen Inc. (or the Registrant) hereby requests acceleration of the effectiveness of the above-referenced Registration Statement pursuant to Rule 461 under the Securities Act of 1933, as amended (or the Securities Act), so that it may become effective on July 2, 2014, at 5:00 p.m., Eastern Time, or as soon thereafter as is practicable.

The Registrant acknowledges that:

•

 should the Securities and Exchange Commission (or the Commission) or the staff, acting pursuant to delegated authority, declare the Registration Statement effective, it does not foreclose the Commission from taking any action with respect to the Registration Statement;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the Registration Statement effective, does not relieve the Registrant from its full responsibility for the adequacy and accuracy of the disclosure in the Registration Statement; and

•

 the Registrant may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

The Registrant understands that the Commission will consider this request for acceleration of the effective date of the Registration Statement as a confirmation of the fact that the Registrant is aware of its responsibilities under the Securities Act, as they relate to the proposed public offering of the securities specified in the Registration Statement.

Very truly yours,

/s/ Bonnie J. Brown

Bonnie J. Brown

Chief Financial Officer

45 First Avenue

Waltham, MA 02451

(781) 466-6400

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		TGN-2014.06.19-Corres Cmt Ltr Rsp 2014 06 19

June 19, 2014

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the “Company”)

Amendment No. 1 to Registration Statement on Form S-1  Filed June 16, 2014 File No. 333-193791

Dear Ms. Long:

The purpose of this letter is to respond to your letter of June 16, 2014 regarding the above registration statement.  For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 2 to the Form S-1.  The Registration Statement on Form S-1, originally filed  on February 6, 2014 (File No. 333-193791), as amended, is referred to herein as the “Registration Statement”.

Principal and Selling Shareholders, page 68

5.

 Please provide a materially complete discussion of how the selling shareholders acquired the securities that you are registering on their behalf for resale. The background of the issuances to the selling shareholders and the nature of the arrangements, agreements, and relationships with the company should include, for each selling shareholder, a discussion of the date of the transaction in which the securities were sold, the amount of securities sold, the agreement(s) that evidence the sale and the instrument(s) that define the rights of the security holders.

Each of the selling shareholders acquired the shares eligible for resale pursuant to the transactions described in the “Principal and Selling Shareholders” section of the Registration Statement.

We have presented in consolidated tabular form a list of each selling shareholder, showing separately for each selling shareholder: each private placement transaction where that shareholder acquired company securities; the number of shares registered on behalf of that shareholder on the S-1; and, in footnotes, a description of the securities which were sold, if other than common stock and any relationship of that shareholder to the company.

6.

 Please disclose any position, office or other material relationship that any selling shareholder has had within the past three years with you or any of your predecessors or affiliates. Refer to Item 507 of Regulation S-K.

We have revised the Principal and Selling Shareholders section to disclose any position, office or other material relationship that any selling shareholder has had within the past three years with us or any of our predecessors or affiliates.

7.

 For any selling shareholder that is not a natural person, please identify by footnote or otherwise the natural person or persons who exercise the sole or shared voting and/or dispositive powers with respect to the shares being offered for resale by the selling shareholder. The following is a non-exhaustive list of selling shareholders for which the requested information should be disclosed:

•

 Michaelson Capital Special Finance Fund;

•

 Citadel Industries, Inc.;

•

 Holme Pierrepoint Fund II LP;

•

 Bourquin Family Trust U/A/D 5-7-98;

•

 Seville Enterprises LP;

•

 Bard Micro-Cap Value Fund LP;

•

 ALB Private Investments, LLC;

•

 Michaelson Capital Special Finance Fund LP;

•

 AEEL LLC; and

•

 Prime World, Inc.

Refer to Question 140.02 of our Regulation S-K Compliance and Disclosure Interpretations.

We have revised our disclosure in the Principal and Selling Shareholders section  and provided footnotes that identify for each selling shareholder that is not a natural person the natural person or persons who exercise the sole or shared voting and/or dispositive powers with respect to the shares being offered for resale by the selling shareholder.

*    *    *

The Company acknowledges that the Company and its management are responsible for the adequacy and accuracy of the disclosures they have made.

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Kamyar Daneshvar, Staff Attorney

Craig Slivka, Special Counsel

June 17 , 2014

Via E -mail
Bonnie Brown
Chief Financial Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Amendment No. 1 to Registration Statement on Form S-1
Filed  June 16, 2014
  File No.  333-193791

Dear Ms. Brown :

We have reviewed your amended registration statement and have the following
comments .

Principal and Selling Shareholders, page 52

1. We note your response to comments five and six in our letter dated February 27, 2014.  It
does not appear that you have revised the principal and selling shareholders section of
your registration statement as requested.  Please advise.

2. We note your respon se to comment seven in our letter dated February 27, 2014.  You
indicate that you have revised your disclosure and “provided footnotes” as requested.
However, it does not appear that you have identified by footnote or otherwise the natural
person or perso ns who exercise sole or shared voting and/or dispositive powers with
respect to the shares being offered for sale by the selling shareholders.  For example,
there is no information provided for Prime World, Inc. or Seville Enterprises LP.  We
reissue comme nt seven in our letter dated February 27, 2014.

You may contact Kamyar Daneshvar, Staff Attorney, at (202) 551 -3787 or Craig Slivka,
Special Counsel,  at (202) 551 -3729 with any questions.

Sincerely,

 /s/ Craig Slivka, for

Pamela Long
Assistant Director

Bonnie Brown
Tecogen Inc.
June 17 , 2014
Page 2

 cc: Edwin L.  Miller (via e -mail)
Sullivan & Worcester LLP

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		TGN-2014.06.13-Corres Cmt Ltr Rsp 2013 02 27

June 13, 2014

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the “Company”)

Registration Statement on Form S-1 Filed February 6, 2014 - File No. 333-193791

Dear Ms. Long:

The purpose of this letter is to respond to your letter of February 27, 2014 regarding the above registration statement.  For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 1 to the Form S-1.  The Registration Statement on Form S-1, originally filed  on February 6, 2014 (File No. 333-193791), as amended, is referred to herein as the “Registration Statement”.

General

1.

 To the extent applicable, please observe the updating requirements of Rule 8-08(b) of Regulation S-X.

We have observed the updating requirements of Rule 8-08(b) of Regulation S-X in the Registration Statement.

2.

 We encourage you to file the legal opinion required by Item 601(b)(5) of Regulation S-K with your next amendment.  Please be aware that we will need sufficient time to review the legal opinion prior to effectiveness of the registration statement.

We have filed the required legal opinion with Amendment No. 1.

Table of Contents

3.

 Please revise your prospectus to remove the statement, “[t]he information in this prospectus is accurate only as of the date of this prospectus, regardless of the time of delivery of this prospectus or any sale of our Common Stock.” This statement may suggest to investors that you are not responsible for omissions of material facts necessary to make your statements not misleading at the time of sale or contract of sale. Information that is conveyed after the time of sale or contract of sale is not taken into account for purposes of section 12(a)(2) or 17(a)(2) of the Securities Act.

We have removed this statement.

Risk Factors, page 8

We could issue additional Common Stock, which might dilute the book value of our Common Stock, page 14

4.

 Please briefly disclose the primary offering in this risk factor.

We closed the primary offering on May 20, 2014.  We respectfully believe that the revised disclosure is no longer necessary.

Principal and Selling Shareholders, page 68

5.

 Please provide a materially complete discussion of how the selling shareholders acquired the securities that you are registering on their behalf for resale. The background of the issuances to the selling shareholders and the nature of the arrangements, agreements, and relationships with the company should include, for each selling shareholder, a discussion of the date of the transaction in which the securities were sold, the amount of securities sold, the agreement(s) that evidence the sale and the instrument(s) that define the rights of the security holders.

Each of the selling shareholders acquired the shares eligible for resale pursuant to the transactions described in the “Principal and Selling Shareholders” section of the Registration Statement.

At the end of this response letter we have presented in consolidated tabular form a list of each selling shareholder, showing separately for each selling shareholder: each private placement transaction where that shareholder acquired company securities; the number of shares registered on behalf of that shareholder on the S-1; and, in notes, a description of the securities which were sold, if other than common stock and any relationship of that shareholder to the company or with another shareholder and any broker-dealer affiliations of the selling shareholders (see Exhibit A).

6.

 Please disclose any position, office or other material relationship that any selling shareholder has had within the past three years with you or any of your predecessors or affiliates. Refer to Item 507 of Regulation S-K.

We have revised the Principal and Selling Shareholders section to disclose any position, office or other material relationship that any selling shareholder has had within the past three years with us or any of our predecessors or affiliates.

7.

 For any selling shareholder that is not a natural person, please identify by footnote or otherwise the natural person or persons who exercise the sole or shared voting and/or dispositive powers with respect to the shares being offered for resale by the selling shareholder. The following is a non-exhaustive list of selling shareholders for which the requested information should be disclosed:

•

 Michaelson Capital Special Finance Fund;

•

 Citadel Industries, Inc.;

•

 Holme Pierrepoint Fund II LP;

•

 Bourquin Family Trust U/A/D 5-7-98;

•

 Seville Enterprises LP;

•

 Bard Micro-Cap Value Fund LP;

•

 ALB Private Investments, LLC;

•

 Michaelson Capital Special Finance Fund LP;

•

 AEEL LLC; and

•

 Prime World, Inc.

Refer to Question 140.02 of our Regulation S-K Compliance and Disclosure Interpretations.

We have revised our disclosure in the Principal and Selling Shareholders section  and provided footnotes that identify for each selling shareholder that is not a natural person the natural person or persons who exercise the sole or shared voting and/or dispositive powers with respect to the shares being offered for resale by the selling shareholder.

*     *    *

The Company acknowledges that the Company and its management are responsible for the adequacy and accuracy of the disclosures they have made.

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Kamyar Daneshvar, Staff Attorney

Craig Slivka, Special Counsel

Exhibit A

Selling Shareholders

 Date of Transaction

 Number of Shares Beneficially

Owned Prior to this Offering

and Being Offered Hereby

Bruno Meier

 10/16/2013

 66,667

Ralph Wanger Trust (1)

 11/6/2013

 200,000

Isac Huberman

 11/6/2013

 11,111

Judith R. Blanton

 11/6/2013

 5,000

D. Roger B. Liddell Revocable Trust (2)

 11/6/2013

 20,000

Adam Boyd Sellers (3)

 11/8/2013

 5,000

Alexis Bard Johnson

 11/8/2013

 7,000

Anne H. Ross

 11/8/2013

 8,000

Carol Clark Coolidge Trust UAD 3-13-97 (4)

 11/8/2013

 7,000

Adam Boyd Sellers Irrevocable Trust DTD 12/19/12 (5)

 11/8/2013

 8,000

Christina D. Collier Living Trust UAD 12/23/03 (5)

 11/8/2013

 5,000

Citadel Industries Inc (6)

 11/8/2013

 5,000

Dale F. Snavely Trust UAD 3/30/93 (7)

 11/8/2013

 12,000

Deborah B. Dewing Trust UAD 6/1/99 (8)

 11/8/2013

 5,000

Christine Elizabeth Coolidge Revocable Living Trust UAD 12/9/02 (9)

 11/8/2013

 5,000

Elliot J. Steinbaum

 11/8/2013

 5,000

Greta Wiley Flory Trust UAD 3/2/04 (10)

 11/8/2013

 5,000

Gary R. Fairhead

 11/8/2013

 5,000

George M. Bard Jr

 11/8/2013

 5,000

Gordon K. Kapes

 11/8/2013

 12,000

Henry J. Underwood Trust U/A/D 6-25-02 (11)

 11/8/2013

 8,000

William K. Kellogg 2011 Trust DTD 1-4-11 FBO Keith W. Kellogg (11)

 11/8/2013

 5,000

William K. Kellogg 2011 Trust DTD 1-4-11 FBO Christopher A. Kellogg(11)

 11/8/2013

 5,000

Holme Pierrepont Fund II LP (12)

 11/8/2013

 5,000

J Scott Etzler

 11/8/2013

 5,000

Janet J. Underwood Trust UAD 6/25/02 (11)

 11/8/2013

 5,000

Jennifer Bard Trust U/A/D 6-30-05 (13)

 11/8/2013

 5,000

John Bard Manulis

 11/8/2013

 5,000

John James Vondran Revocable Trust UAD 1-24-11 (14)

 11/8/2013

 5,000

Bourquin Family Trust U/A/D 5-7-98 (15)

 11/8/2013

 8,000

Katherine Bard Dickson & Mark A Dickson JTWROS

 11/8/2013

 25,000

(1)

 Shares held by Ralph Wanger Trust were purchased under the control of Ralph Wanger.

(2)

 Shares held by D. Roger B. Liddell Revocable Trust were purchased under the control of Roger Liddell.

(3)

 Shares held by Adam Boyd Sellers were purchased under the control of Adam Boyd.

(4)

 Shares held by Carol Clark Coolidge Trust were purchased under the control of Carol Clark.

(5)

 Shares held by Adam Boyd Sellers Irrevocable Trust or Christina D. Collier Living Trust were purchased under the control of Christina Collier.

(6)

 Shares held by Citadel Industries Inc. were purchased with the signatory authority of James Boddy.

(7)

 Shares held by Dale F. Snavely Trust were purchased under the control of Dale F. Snavely.

(8)

 Shares held by Deborah B. Dewing Trust were purchased under the control of Deborah B. Dewing.

(9)

 Shares held by Christine Elizabeth Coolidge Revocable Living Trust were purchased under the control of  Dexter Coolidge.

(10)

 Shares held by Greta Wiley Flory Trust were purchased under the control of Greta Wiley Flory.

(11)

 Shares held by Henry J. Underwood Trust, Janet J. Underwood Trust and the William K. Kellogg 2011 Trusts FBO Keith W. Kellogg and FBO Christopher A. Kellogg were purchased under the control of  Henry Underwood.

(12)

 Shares held by Holme Pierrepont Fund II LP were purchased under the control of Seth Pierrepont.

(13)

 Shares held by Jennifer Bard Trust were purchased under the control of Jennifer Bard.

(14)

 Shares held by John James Vondran Revocable Trust were purchased under the control of John Vondran.

(15)

 Shares held by Bourquin Family Trust with the signatory authority of Kent Bourquin.

Exhibit A

Selling Shareholders (Continued)

 Date of Transaction

 Number of Shares Beneficially

Owned Prior to this Offering

and Being Offered Hereby

Laurie M. Harmon Trust U/A/D 9-12-96 (1)

 11/8/2013

 5,000

Leonard M. Herman Trust UAD 5/3/93 (2)

 11/8/2013

 12,000

M Edward Sellers & Suzan D Boyd JTWROS

 11/8/2013

 25,000

Marcia E. Cremin Revocable Trust U/A/D 3-1-06 (3)

 11/8/2013

 5,000

Marshall I. Steinbaum

 11/8/2013

 5,000

Marvin J. Pollack

 11/8/2013

 5,000

Mary M. Schwartz Trust U/A/D 9-5-06 (4)

 11/8/2013

 8,000

Matthew Moog

 11/8/2013

 5,000

Michael D. Watt Trust U/A/D 3-15-12 (5)

 11/8/2013

 5,000

R. Stuyvesant Pierrepont Jr 1932 Trust (6)

 11/8/2013

 5,000

Steinbaum Family Trust U/W Paul S. Steinbaum (7)

 11/8/2013

 8,000

Catherine Konner Trust U/W C. Konner FBO H Garfinkle (7)

 11/8/2013

 5,000

Robert E. Logan Jr

 11/8/2013

 5,600

Consuelo Diane Pierrepont Irrevocable Trust DTD 2/3/99 (6)

 11/8/2013

 5,000

Nathalie Rutherford Pierrepont Irrevocable Trust DTD 2/12/03 (6)

 11/8/2013

 5,000

Seth Low Pierrepont, Jr Irrevocable Trust DTD 4/15/01 (6)

 11/8/2013

 5,000

Seville Enterprises LP (8)

 11/8/2013

 5,000

Stuart S. Carey

 11/8/2013

 5,000

Susan W. McMillan Trust U/A/D 10-10-71 (9)

 11/8/2013

 5,000

Suzanne R. Davis

 11/8/2013

 5,000

T Michael Johnson & Patricia R Johnson JTWROS

 11/8/2013

 5,000

Tom Kenworthy & Nancy Kenworth JTWROS

 11/8/2013

 5,000

William G. Escamilla Revocable Trust DTD 7/29/03 (10)

 11/8/2013

 5,000

William K. Kellogg Trust U/A/D 7-24-92 (11)

 11/8/2013

 25,000

Sidney N. Herman

 11/8/2013

 25,000

Anne R. Brown Irrevocable Trust UAD 3-30-90 (12)

 11/8/2013

 8,000

Timothy B. Johnson

 11/8/2013

 25,000

Bard Micro-Cap Value Fund LP (13)

 11/8/2013

 25,000

Mary A. Heatter Trust UAD 6/28/04 (14)

 11/8/2013

 5,000

Mary Elizabeth McAvoy Trust UAD 9-5-84 (15)

 11/19/2013

 2,500

Marc Edwin Nicholson

 11/19/2013

 4,000

(1)

 Shares held by Laurie M. Harmon Trust were purchased under the control of Laurie M. Harmon.

(2)

 Shares held by Leonard M. Herman Trust were purchased under the control of Leonard M. Herman.

(3)

 Shares held by Marcia E. Cremin Revocable Trust were purchased under the control of Marcia E. Cremin.

(4)

 Shares held by Mary M. Schwartz Trust were purchased under the control of Mary M. Schwartz.

(5)

 Shares held by Michael D. Watt Trust were purchased under the control of Michael D. Watt.

(6)

 Shares held by R. Stuyvesant Pierrepont Jr 1932 Trust, Consuelo Diane Pierrepont Irrevocable Trust, Nathalie Rutherford Pierrepont Irrevocable Trust, and Seth Low Pierrepont, Jr Irrevocable Trust were purchased under the control of Seth Pierrepont.

(7)

 Shares held by Steinbaum Family Trust and Catherine Konner Trust were purchased under the control of Robert Steinbaum.

(8)

 Shares held by Seville Enterprises LP were purchased under the signatory authority of Marvin Pollack.

(9)

 Shares held by Susan W. McMillan Trust were purchased under the control of Susan W. McMillan.

(10)

 Shares held by William G. Escamilla Revocable Trust were purchased under the control of William G. Escamilla.

(11)

 Shares held by William K. Kellogg Trust were purchased under the control of William K. Kellogg.

(12)

 Shares held by Anne R. Brown Irrevocable Trust were purchased under the control of Anne R. Brown.

(13)

 Shares held by Bard Micro-Cap Value Fund LP were purchased under the signatory authority of Timothy B. Johnson.

(14)

 Shares held by Mary A. Heatter Trust were purchased under the control of Mary A. Heatter.

(15)

 Shares held by Mary Elizabeth McAvoy Trust were purchased under the control of Mary Elizabeth McAvoy.

Exhibit A

Selling Shareholders (Continued)

 Date of Transaction

 Number of Shares Beneficially

Owned Prior to this Offering

and Being Offered Hereby

Rosemary Steinbaum

 11/19/2013

 5,000

Robert S. Steinbaum

 11/19/2013

 5,000

Julien D. LeBourgeois

 11/19/2013

 2,500

Anthony B. Low-Beer

 11/25/2013

 27,500

Helen R. Esposito

 11/25/2013

 15,000

John F. Kohn

 11/25/2013

 10,000

Phylis M. Esposito

 11/25/2013

 60,000

Maida Chicon

 11/25/2013

 10,000

Cynthia A. Kohn

 11/25/2013

 15,000

ALB Private Investments, LLC (1)

 11/25/2013

 26,250

Edward Nersessian Profit Sharing Plan E. Nersessian MD & M Luallen-Nersessian PHD TTEES (2)

 11/25/2013

 15,000

John R. Low-Beer

 11/25/2013

 15,000

IRA FBO Norman S. Heyman Pershing LLC as Custodian (3)

 11/27/2013

 14,400

Thomas M. Gehret

 12/2/2013

 1,250

Sarah E. Gehret

 12/2/2013

 1,250

J Edward Diamond

 12/16/2013

 3,000

Kurt A. Dasse

 12/18/2013

 14,866

Patricia Hatsopoulos(4)

 12/19/2013

 100

Michaelson Capital Special Finance Fund LP (shares owned) (5)

 12/23/2013

 444,445

Michaelson Capital Special Finance Fund LP (shares issuable on conversion of convertible debt)(5)

 12/23/2013

 555,556

Torrey B.W. Liddell Revocable Trust (6)

 12/23/2013

 7,800

AEEL LLC (6)

 12/23/2013

 6,700

Robert Prosser

 12/23/2013

 2,250

Jeb S. Armstrong

 12/23/2013

 1,700

Donald B. Brant Jr.

 12/23/2013

 5,600

Eleanor H. Bishop Revocable Trust (7)

 12/23/2013

 6,000

Catherine S. Woolston SEP IRA

 12/24/2013

 2,250

Mark Sherrid IRA

 12/24/2013

 1,000

George Michael Gehret

 12/24/2013

 450

Prime World, Inc. (8)

 12/30/2013

 1,000

Dorothy Heyman

 1/7/2014

 1,000

John H. Jephson (9)

 1/10/2014

 100

Yiannis Monovoukas, Ph.D.

 1/15/2014

 100

Craig A. Drill

 1/17/2014

 100

Monica K. Drill, MD

 1/17/2014

 100

(1)

 Shares held by ALB Private Investments were purchased the signatory authority of Anthony Low-Beer, a registered broker dealer.

(2)

 Shares held by Edward Nersessian Profit Sharing Plan were purchased under the control of Edward Nersessian and Nancy Nelson.

(3)

 Shares held by IRA FBO Norman S. Heyman Pershing LLC were purchased under the control of Norman S. Heyman.

(4)

 Shares held by Patricia L. Hatsopoulos, insider and Chief Executive Officer John N. Hatsopoulos’s spouse.

(5)

 Shares held by a 5% shareholder listed in the 5% holders table and controlled by John C. Michaelson.

(6)

 Shares held by Torrey B. W. Liddell Revocable Trust and AEEL LLC were purchased under the control and signature authority of Roger Liddell.

(7)

 Shares held by Eleanor H. Bishop Revocable Trust were purchased under the control of Eleanor H. Bishop.

CORRESP
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		TGN 2014 05 08 Corres - Accel Request S-1 Effect

May 8, 2014

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:    Tecogen Inc.Registration Statement on Form S-1 (or the Registration Statement) No. 333-193823

Ladies and Gentlemen:

Tecogen Inc. (or the Registrant) hereby requests acceleration of the effectiveness of the above-referenced Registration Statement pursuant to Rule 461 under the Securities Act of 1933, as amended (or the Securities Act), so that it may become effective on May 12, 2014, at 5:00 p.m., Eastern Time, or as soon thereafter as is practicable.

The Registrant acknowledges that:

•

 should the Securities and Exchange Commission (or the Commission) or the staff, acting pursuant to delegated authority, declare the Registration Statement effective, it does not foreclose the Commission from taking any action with respect to the Registration Statement;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the Registration Statement effective, does not relieve the Registrant from its full responsibility for the adequacy and accuracy of the disclosure in the Registration Statement; and

•

 the Registrant may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

The Registrant understands that the Commission will consider this request for acceleration of the effective date of the Registration Statement as a confirmation of the fact that the Registrant is aware of its responsibilities under the Securities Act, as they relate to the proposed public offering of the securities specified in the Registration Statement.

Very truly yours,

/s/ Bonnie J. Brown

Bonnie J. Brown

Chief Financial Officer

45 First Avenue

Waltham, MA 02451

(781) 466-6400

CORRESP
1
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		TGN 2014 05 08 Corres - Accel Request - Scarsdale

May 8, 2014

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, N.E.

Washington, D.C. 20549

Re:    Tecogen Inc.

Registration Statement on Form S-1 (or the Registration Statement)

Registration File No. 333-193823

Ladies and Gentlemen:

In accordance with Rule 461 of the General Rules and Regulations under the Securities Act of 1933, as amended (the “Act”), the undersigned, as the Placement Agent, hereby joins in the request of Tecogen Inc. (the “Company”) for acceleration of the effective date of the above-named Registration Statement so that it becomes effective at 5:00 p.m., Eastern Time, on Monday, May 12, 2014, or as soon thereafter as practicable.

Pursuant to Rule 460 of the Act, please be advised that through the date hereof, the undersigned effected the distribution of approximately 240 copies of the Company’s Preliminary Prospectus, dated April 23, 2014 to prospective investors, dealers and others.

This is to further advise you that the undersigned has complied and will continue to comply with Rule 15c2-8 under the Securities Exchange Act of 1934, as amended.

[Signature Page Follows]

Very truly yours,

SCARSDALE EQUITIES LLC

By:

 /s/ Francis A. Mlynarczyk, Jr.

 Name:  Francis A. Mlynarczyk, Jr.

 Title:

 Chief Executive Officer

April 21 , 2014

Via E -Mail
Bonnie Brown
Chief Financial Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Amendment No. 1 to Registration Statement on Form S-1
Filed  April 17, 2014
  File No.  333-193823

Dear Ms. Brown :

We have reviewed your amended registration statement and have the following
comments .

Use of Proceeds, page 20

1. Please remove the apparent inadvertent inclusion of “million” after “$500,000” in the
first paragraph o n page 20 , or advise .

2. We note your response to comment 7 in our letter dated February 27, 2014.  Your
proposed revised disclosure set forth in your response letter does not appear in the
registration statement.  Please advise.

Exhibit Index

3. We note that you have not included XBRL tagged financials as exhibits to your
registration statement.  Rather, you make reference to the XBRL information in your
annual report on Form 10 -K for the fiscal year ended December 31, 2013 .  Please in clude
electronically tagged Interactive Data Files with your next amendment.

Bonnie Brown
Tecogen Inc.
April 21 , 2014
Page 2

 You may contact Kamyar Daneshvar, Staff Attorney, at (202) 551 -3787 or Craig Slivka,
Special Counsel,  at (202) 551 -3729 with any questions.

Sincerely,

 /s/ Craig Slivka, for

Pamela Long
Assistant Director

cc: Edwin L.  Miller (via e -mail)
 Sullivan & Worcester LLP

February 27, 2014

Via E -mail
Bonnie Brown
Chief Financial Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen Inc.
  Registration Statement on Form S-1
Filed  February 7, 2014
  File No.  333-193823

Dear Ms. Brown :

We have limited our review of your registration statement to those issues we have
addressed in our comments.  In  some of our comments, we may ask you to provide us with
information so we may better understand your disclosure.

Please respond to this letter by amending your registration statement and providing the
requested information .  Where you do not believe our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.

After reviewing any amendment to your registration statement and the information you
provide in response to these  comments , we may have  additional comments.

General

1. To the extent applicable, please observe the updating requirements of Rule 8 -08(b) of
Regulation S -X.

2. We note that you intend to file by amendment certain exhibits, including the placement
agent agreement, fo rm of securities purchase agreement and the legal opinion.  We may
have comments on the opinion and other exhibits after they are filed.   Please allow
sufficient time for staff review of these materials before requesting acceleration of
effectiveness of t he registration statement.

3. We will process this registration statement and any amendment without a price range.
Since the price range triggers a number of disclosure matters, we will need sufficient time
to process the amendment in which it is included.  Note that the price range’s effect on

Bonnie Brown
Tecogen Inc.
February 27, 2014
Page 2

 disclosure throughout the registration statement may cause us to raise issues on areas
upon which we have not commented previously.

4. As indicated in the comment above, we note that you have omitted certain pricing -related
information as well as other information.  If you intend to rely on Rule 430A of
Regulation C under the Securities Act, please note that Rule 430A does not allow for the
omission before effectiveness of amounts that may be computed based on the maximum
number of shares offered and the midpoint of the offering price range or the number of
shares to be offered on the cover page.  Also, please confirm that you will not circulate
copies of the registration statement or the preliminary prospectus until you i nclude an
estimated price range, maximum number of shares, dollar amounts dependent upon the
offering price that are based on the midpoint of the offering price range, and all other
information except information that you may exclude in reliance upon Rule 430A.  For
additional guidance, please see Compliance and Disclosure Interpretations Securities Act
Rules Question 227.02.

5. We note that the placement agent will use its “commercially reasonable efforts to solicit
offers to purchase shares of Common Stock ” and that the placement agent “is not
purchasing or selling any shares of Common Stock pursuant to this offering, nor are
[you] requiring any minimum purchase of any specific number of shares.”  As there is no
minimum offering amount required as a conditi on to the closing of the offering, please
provide us with your analysis as to why this is not a delayed or continuous offering
pursuant to Rule 415 under the Securities Act.

Table of Contents

6. Please revise your prospectus to remove the statement, “[t]he information in this
prospectus is accurate only as of the date of this prospectus, regardless of the time of
delivery of this prospectus or any sale of our Common Stock.”  This statement may
suggest to investors that you are not responsible for omissions o f material facts necessary
to make your statements not misleading at the time of sale or contract of sale.
Information that is conveyed after the time of sale or contract of sale is not taken into
account for purposes of section 12(a)(2) or 17(a)(2) of th e Securities Act.

Use of Proceeds, page 20

7. Please discuss your plans if substantially less than the maximum proceeds are obtained.
Refer to Instruction 1 to Item 504 of Regulation S -K.

We urge all persons who are responsible for the accuracy and adequacy of the disclosure
in the filing to be certain that the filing includes the information the Securities Act of 193 3 and
all applicable Securities  Act rules require.   Since the company and its management are in
possession of all facts relating to a company’s disclosure, they are responsible for the accuracy
and adequacy of the disclosures they have made.

Bonnie Brown
Tecogen Inc.
February 27, 2014
Page 3

Notwithstanding our comments, in the event you request accelera tion of the effective date
of the pending registration statement please provide a written statement from the company
acknowledging that:

 should the Commission or the staff, acting pursuant to delegated authority, declare the
filing effective, it does not foreclose the Commission from taking any action with respect
to the filing;

 the action of the Commission or the staff, acting pursuant to delegated authority, in
declaring the filing effective, does not relieve the company from its full responsibility fo r
the adequacy and accuracy of the disclosure in the filing; and

 the company may not assert staff comments and the declaration of effectiveness as a
defense in any proceeding initiated by the Commission or any person under the federal
securities laws of the United States.

Please refer to Rules 460 and 461 regarding requests for  acceleration .  We will consider a
written request for acceleration of the effective date of the registration statement as confirmation
of the fact that those requesting accelerati on are aware of their respective responsibilities under
the Securities Act of 1933 and the Securities Exchange Act of 1934 as they relate to the proposed
public offering of the securities specified in the above registration statement.  Please allow
adequat e time  for us to review any amendment prior to the requested effective date of the
registration statement.

You may contact Kamyar Daneshvar, Staff Attorney, at (202) 551 -3787 or Craig Slivka,
Special Counsel,  at (202) 551 -3729 with any questions.

Sincerely,

 /s/ Craig Slivka, for

Pamela Long
Assistant Director

cc: Edwin L.  Miller (via e -mail)
 Sullivan & Worcester LLP

CORRESP
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		TGN Accel Req S-1 2013.02.14

February 14, 2012

Via EDGAR

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:    Tecogen Inc.

Registration Statement on Form S-1 (or the Registration Statement)

No. 333-178697

Ladies and Gentlemen:

Tecogen Inc. (or the Registrant) hereby requests acceleration of the effectiveness of the above-referenced Registration Statement pursuant to Rule 461 under the Securities Act of 1933, as amended (or the Securities Act), so that it may become effective on February 14, 2013, at 4:30 p.m., Eastern Time, or as soon thereafter as is practicable.

The Registrant acknowledges that:

•

 should the Securities and Exchange Commission (or the Commission) or the staff, acting pursuant to delegated authority, declare the Registration Statement effective, it does not foreclose the Commission from taking any action with respect to the Registration Statement;

•

 the action of the Commission or the staff, acting pursuant to delegated authority, in declaring the Registration Statement effective, does not relieve the Registrant from its full responsibility for the adequacy and accuracy of the disclosure in the Registration Statement; and

•

 the Registrant may not assert staff comments and the declaration of effectiveness as a defense in any proceeding initiated by the Commission or any person under the federal securities laws of the United States.

The Registrant understands that the Commission will consider this request for acceleration of the effective date of the Registration Statement as a confirmation of the fact that the Registrant is aware of its responsibilities under the Securities Act, as they relate to the proposed public offering of the securities specified in the Registration Statement.

Very truly yours,

/s/ Bonnie J. Brown

Bonnie J. Brown

Chief Financial Officer

Tecogen Inc.

45 First Avenue

Waltham, MA  02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

CORRESP
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		TGN RESPONSE 8 2013.02.14

February 14, 2013

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the Company)

Amendment No. 7 to Registration Statement

No. 333-178697

Dear Ms. Long:

The purpose of this letter is to respond to your letter of February 13, 2013 regarding the above registration statement. For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 8 to the Form S-1.

Exhibit 23.1 Consent of Independent Registered Public Accounting Firm

1.

 We note your auditor’s consent references Amendment 6. Please request your auditors to provide a consent that references the appropriate filing.

We have revised our disclosure as requested to include our auditor’s consent that references the appropriate filing.

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Mindy Hooker, Staff Accountant

Jeanne Baker, Staff Accountant

Erin Jaskot, Staff Attorney

Craig Slivka, Special Counsel

Tecogen Inc.

45 First Avenue

Waltham, MA  02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

February 13 , 2013

Via E -mail
John N. Hatsopoulos
Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen  Inc.
Amendment No. 7 to Registration Statement on Form S -1
Filed February 11, 2013
  File No. 333 -178697

Dear Mr.  Hatsopoulos :

We have reviewed  your response letter and the above -referenced filing,  and have the
following comment .

Exhibit 23.1 Consent of Independent Registered Public Accounting Firm

1. We note your auditor’s consent references Amendment 6.  Please request your auditors to
provide a consent that references the appropriate filing.

As appropriate, please amend your registration statement in response to these comments.
You may wish to  provide us with marked copies of the amendment to expedite our review.
Please furnish a cover letter with your amendment that keys your responses to our comments and
provides any requested information. Detailed cover letters greatly facilitate our review.  Please
understand that we may have additional comments after reviewing your amendment and
responses to our comments.

You may contact Mindy Hooker , Staff Accou ntant, at 202 -551-3732, or Jeanne Baker ,
Staff Accountant , at 202 -551-3691 if you  have questions regarding comments on the financial
statements and related matters.  Please contact Erin Jaskot, Staff Attorney,  at 202-551-3442,  or
Craig Slivka , Special Counsel,  at 202-551-3729 with any other questions.

Sincerely,

 /s/ Craig E. Slivka, for

Pamela A. Long
Assistant Director

cc:   Kristen A. Young , Esq. ( via E-mail)

John N. Hatsopoulos
Tecogen Inc.
February 13 , 2013
Page 2

 Sullivan & Worcester  LLP

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		TGN Response CTR/AMD7 2013.02.11

February 11, 2013

Via EDGAR

Craig Slivka, Special Counsel

Securities and Exchange Commission

Division of Corporation Finance

100 F. Street, N.E.

Washington, DC 20549

Re:

 Tecogen, Inc. (the Company)

Amendment No.6 to Registration Statement and Confidential Treatment Application

No. 333-178697

Dear Mr. Slivka:

The purpose of this letter is to respond to your letter of February 6, 2013 regarding the above Registration Statement and Confidential Treatment Application. For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 7 to the Form S-1 and revised Confidential Treatment Requests.

General

1.

 Except in unusual circumstances, disclosure required by Regulation S-K or any other applicable disclosure requirement is not appropriate subject matter for confidential treatment. In particular, confidential treatment of related party contracts covered by Item 404 of Regulation S-K is not usually appropriate.  Refer to Item II.B.2 of Staff Legal Bulletin No. 1 and footnote 18 thereto. We note that Exhibits 10.6 and 10.14 are agreements with American DG Energy Inc. and Ilios Dynamics, both of which involve related parties. Please note that all provisions of the agreements that define significant rights and obligations should be made available to investors. Please revise your application accordingly.

We have limited our request for confidential treatment to certain, specific pricing terms.  Notwithstanding Item II.B.2 Staff Legal Bulletin No. 1 (“SLB 1”), such terms are of the sort specifically identified in SLB 1 for which confidential treatment is typically granted.  While we acknowledge that confidential treatment of related party contracts covered by Item 404 of Regulation S-K is not usually appropriate, because such specific terms would not be required to be disclosed pursuant to Item 404, we feel confidential treatment is appropriate in this case.  As described in our amended application, such terms are consistent with those we have negotiated with certain other, unrelated third-parties.  If we are required to disclose such terms, our ability to negotiate competitive pricing terms in the future would be damaged and we would suffer substantial competitive harm.

Securities and Exchange Commission

February 11, 2013

2.

 Please revise your application for each exhibit to discuss in more detail why the specific information redacted is not material to investors.

We have revised our application to discuss in more detail why the specific information redacted is not material to investors.

Exhibit 10.11 - Asset Purchase Agreement

3.

 We note that your disclosure in the registration statement states that you have purchased from Danotek the assets required to manufacture the permanent magnet generator used in your InVerde product. However, it appears that your agreement with Danotek is related to Danotek’s assignment of all of its property to you for the benefit of Danotek’s creditors. Please revise the disclosure in your registration statement to provide a materially complete description of the agreement, including the significance of the assignment and any material obligations you have assumed pursuant to the agreements.

In connection with assignment for the benefit of creditors proceedings, all of the assets of Danotek Motion Technologies Inc. (“Danotek Inc.”) was assigned to a newly created entity, Danotek (assignment for the benefit of creditors), LLC (“Danotek LLC”).  The board of directors of Danotek Inc. engaged Sherwood Partners, LLC to liquidate such assets.  Tecogen purchased a portion of such assets, specifically those required to manufacture the DMT 5300 product line, from Danotek LLC.  Other than as set forth in Exhibit 10.11 and in the Registration Statement, Tecogen has no relationship with Danotek Inc., Danotek LLC or Sherwood Partners, LLC.

4.

 Please provide us with a more complete analysis as to why the disclosure of the redacted information in the second paragraph of Section 2.1 would cause the company substantial competitive harm in view of the specific circumstances applicable to the company.

We have revised our application to include a more complete analysis as to why the disclosure of the redacted information in the second paragraph of Section 2.1 would cause us substantial competitive harm in view of the specific circumstances applicable to us.

5.

 In your amended application, please indicate the terms that you propose to redact from Section 9.1. We note that certain terms in this section have been redacted in the publicly-filed version.

We have revised our application to indicate the terms that we propose to redact from Section 9.1.

6.

 We note that you have redacted all of Section 3.1 and Schedule A and Schedule B. Confidential treatment is generally granted only for specific sentences, words, or figures and not granted for entire paragraphs, sections, or attachments. Please revise your application so that only those terms that would cause the company substantial competitive harm are redacted.

We have revised our application to more narrowly tailor our redactions in Section 3.1 and Schedule A and Schedule B.  With respect to Schedule A and Schedule B, we have redacted only those portions which would enable to the reader to identify the listed patents.

Page2

Securities and Exchange Commission

February 11, 2013

Exhibit 10.12 - Exclusive License Agreement

7.

 Please revise your registration statement to disclose the material terms of the agreement. In addition, to the extent material, please disclose the aggregate annual amount of the royalty payments that you have made to the Wisconsin Alumni Research Foundation.

We have revised our disclosure as requested to include the material terms of the agreement and the annual amount of royalty payments through the year ended December 31, 2012.

8.

 We note that your application states that you have redacted terms in Appendix B, however it does not appear that you have redacted any such terms. Please revise your application accordingly.

We have revised our application accordingly.

9.

 It is unclear why you have requested that the redacted information remain confidential until December 31, 2017. Please advise.

We have requested confidential treatment with respect to Exhibit 10.12 for the term of such agreement.  Unless earlier terminated accordance with its terms, Exhibit 10.12 will expire upon the date that no Licensed Patent (as defined in Exhibit 10.12) remains an enforceable patent or the payment of earned royalties under Section 4B of Exhibit 10.12, once begun, ceases for more than eight consecutive calendar quarters.  The last of the Licensed Patents is expected to expire on December 31, 2017.  We expect to pay royalties under Exhibit 10.12 with such frequency that Exhibit 10.12 would not otherwise be terminated prior to December 31, 2017.

Exhibit 10.13 - Grant Award Number PIR-08-022

10.

 Please revise your registration statement to disclosure the material terms of the grant, including, to the extent material, the potential range of royalty payments (for example, "1ow-single-digits") as specified in Section 25.a.

We have revised our disclosure as requested to include the material terms of the agreement and the range of royalty payments on an annual basis through the year ended December 31, 2012.

11. It appears that the graph on page 51 of your agreement is not in the publicly filed version of the agreement. Please ensure that the publicly filed version includes all parts of the agreement that are not redacted.

We are refiling Exhibit 10.13 to include the referenced graph.

12. We note that you have redacted all of page 51 with the exception of the title, "Budget.” Please revise your application so that you redact only those terms that would cause the company substantial competitive harm if disclosed.

We have revised our application to disclose all of the previously redacted information under the title “Budget.”

Page3

Securities and Exchange Commission

February 11, 2013

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Pamela Long, Assistant Director

Mindy Hooker, Staff Accountant

Jeanne Baker, Staff Accountant

Erin Jaskot, Staff Attorney

Page4

CORRESP
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		TGN RESPONSE 6 2013.02.05

Securities and Exchange Commission

February 5, 2013

Page 1

February 5, 2013

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc. (the Company)

Amendment No.5 to Registration Statement

No. 333-178697

Dear Ms. Long:

The purpose of this letter is to respond to your letter of January 25, 2013 regarding the above registration statement. For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 6 to the Form S-1.

General

1.

 In your next amendment, please include the delaying amendment language in Rule 473 of the Securities Act.

We have revised our disclosure as requested to include the delaying amendment language in Rule 473 of the Securities Act.

Executive Officer and Director Compensation, page 62

2.

 Please update the compensation disclosure in the filing to reflect compensation for the year ended December 31, 2012, which is your most recently completed fiscal year. Please note that you must also continue to disclose the compensation for the year ended December 31, 2011. Refer to Item 402 of Regulation S-K.

We have revised our disclosure as requested to include compensation for the year ended December 31, 2012.

Note 9 - Subsequent Events, page F-15

3.

 We note your disclosure indicating that on January 9, 2013 you purchased the assets, both tangible and intangible, required to manufacture the permanent magnet generator (PMG) used in your InVerde product. Please disclose the purchase price of this acquisition and with reference to Rule 11-01(d) and ASC Topic 805-50-10, please tell us what consideration you have given to including financial statements of businesses acquired under Rule 8-04 of Regulation S-X and the related pro forma financial information required by Rule 8-05 of Regulation S-X. Refer to Part I, Item 11(e) of Form S-1.

Tecogen Inc.

45 First Avenue

Waltham, MA  02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

Securities and Exchange Commission

February 5, 2013

Page 2

The Asset Purchase Agreement between the Company and Danotek LLC, or Danotek, included a requirement to keep the financial details of the transaction confidential for a period of six months. We have requested confidential treatment of the Asset Purchase Agreement under Rule 406 promulgated under the Securities Act of 1933, as amended.

In accordance with Rule 11-01(d) and ASC Topic 805 under Rule 8-04 of Regulation S-X, we determined that pro forma financial information would not be required for the following reasons. Danotek produced a generator that the Company uses in its InVerde 100 unit. There is no other market or customers for this generator. Danotek, currently under “Assignment for the Benefit of Creditors”, manufactured other generator lines for its customers, but the Company did not purchase any of these components. For the Company, this purchase of the DMT5300 product line is considered an asset and not a business; there will be no revenue generated from this product line. For Danotek, this product line was not considered a separate entity, subsidiary or division; it was simply one product of many that it developed and manufactured.

Furthermore, the manufacturing operation will be moved to the Company's facilities and the generators will be manufactured by the Company's personnel. No Danotek employees were hired by the Company. As part of the purchase, Danotek's employees provided the Company's employees with production techniques by allowing them to view and participate in the final production runs of the generators at Danotek's facility in Michigan. There were no market distribution systems, sales force, customer base, operating rights or trade names purchased as the Company simply purchased the equipment, documentation, rights and know how required to build these generators in house. The Company has engaged a professional valuation advisor to assist in valuing each tangible and intangible asset purchased. For the above reasons, the Company has determined that pro forma financial information is not required in accordance with Rule 11-01(d) and ASC Topic 805 under Rule 8-04 of Regulation S-X.

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Mindy Hooker, Staff Accountant

Jeanne Baker, Staff Accountant

Erin Jaskot, Staff Attorney

Craig Slivka, Special Counsel

Tecogen Inc.

45 First Avenue

Waltham, MA  02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

January 25, 2013

Via E -mail
John N. Hatsopoulos
Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen  Inc.
Amendment No. 5 to Registration Statement on Form S -1
Filed January 15, 2013
  File No. 333 -178697

Dear Mr.  Hatsopoulos :

We have reviewed  your response letter and the above -referenced filing, and have the
following comments.

Amendment No. 5 to Registration Statement on Form S -1

General

1. In your next amendment, please include the delaying amendment language in Rule 473 of
the Securities Act.

Executive Officer and Director Compensation, page 62

2. Please update the compensation disclosure in the filing to reflect compensation for the
year ended  December 31, 201 2, which is your most recently completed fiscal year.
Please note that you must also continue to disclose the compensation for the year ended
December 31, 2011.   Refer to Item 402 of Regulation S -K.

Note 9 - Subsequent Events , page F -15

3. We note your disclosure indicating that on January 9, 2013 you purchased the assets, both
tangible and intangible, required to manufacture the permanent magnet generator (PMG)
used in your InVerde product. Please disclose the purchase price of this acquis ition and
with reference to Rule 11 -01(d) and ASC Topic 805 -50-10, p lease tell us what
consideration you have given to including financial statements of businesses acquired
under Rule 8 -04 of Regulation S -X and the related pro forma financial information
required by Rule 8 -05 of Regulation S -X.  Refer to Part I, Item 11(e) of Form S -1.

John N. Hatsopoulos
Tecogen Inc.
January 25 , 2013
Page 2

 As appropriate, please amend your registration statement in response to these comments.
You may wish to provide us with marked copies of the amendment to expedite our review.
Please furnish a cover letter with your amendment that keys your responses to our  comments and
provides any requested information. Detailed cover letters greatly facilitate our review. Please
understand that we may have additional comments after reviewing your amendment and
responses to our comments.

You may contact Mindy Hooker , Staff Accou ntant, at 202 -551-3732, or Jeanne Baker ,
Staff Accountant , at 202 -551-3691 if you  have questions regarding comments on the financial
statements and related matters.  Please contact Erin Jaskot, Staff Attorney,  at 202-551-3442,  or
Craig Slivka , Special Counsel,  at 202-551-3729 with any other questions.

Sincerely,

 /s/ Craig E. Slivka, for

Pamela A. Long
Assistant Director

cc:   Kristen A. Young , Esq. ( via E-mail)
Sullivan & Worcester  LLP

CORRESP
1
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		TGN RESPONSE 5 2013.01.15

January 15, 2013

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc.

Amendment No.4 to Registration Statement

No. 333-178697

Dear Ms. Long:

The purpose of this letter is to respond to your letter of January 4, 2013 regarding the above registration statement. For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 5 to the Form S-1.

Management’s Discussion and Analysis of Financial Condition and Results of Operations, page 48

Results of Operations, page 52

1.

 We note that your selling expense has increased significantly over the periods presented. In this regard, we also note that as a percentage of revenues, selling expense was 2.6%, 7.1% and 9.5% of revenues for 2010, 2011 and the nine months ended September 30, 2012. Please expand your disclosures to explain reasons for these increases and the nature of the costs included in selling expense.

We have revised our disclosure as requested to include the reasons for the fluctuation in our selling expenses. The new section on page 52 reads as follows:

"Selling expenses within this category increased in the first nine months of 2012 to $915,842 compared to $381,617 for the same period in 2011, an increase of $534,225 due to the Company's efforts in creating a stronger sales and marketing team which began during 2011. This effort included hiring new personnel for both sales and marketing and hiring a public relations firm. In addition to the above, during the nine months ended September 30 2012 the Company invested approximately $155,000 in trade shows and a traveling “road show” where three of the Company's products were showcased on an enclosed trailer which traveled up and down the west coast. During the same period in 2011 the Company incurred approximately $31,000 in trade show expenses."

Tecogen Inc.

45 First Avenue

Waltham, MA  02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

Securities and Exchange Commission

January 15, 2013

Page 2

The new section on page 54 reads as follows:

"Selling expenses for the years ended December 31, 2011 and 2010 were $782,252 and $290,505, respectively, an increase of $491,747. Approximately $200,000 of this increase is due to an increase in commission costs in 2011 since the Company experienced more commissionable sales during this period. The balance was due to the Company's efforts in creating a stronger sales and marketing team which began during 2011. This effort included hiring new personnel for both sales and marketing and hiring a public relations firm."

Security Ownership of Certain Beneficial Owners and Management, page 69

2.

 Please update your disclosure to present security ownership as of the most recent practicable date. See Item 403 of Regulation S-K.

We have revised our disclosure as requested in the Security Ownership of Certain Beneficial Owners and Management Table to include that the percentages are based on 54,417,854 shares of Common Stock issued and outstanding as of January 15, 2013.

Recent Sales of Unregistered Securities, page F-39

3.

 We note your disclosure in Note 3 on page F-10 that on September 30, 2012 certain holders of the debentures converted the principal amount and accrued interest on the debentures into shares of the company’s common stock. Please include the disclosure required by Item 701 of Regulation S-K with respect to this issuance of common stock, including the applicable exemption from registration.

We have revised our disclosure on Item 15. Recent Sales of Unregistered Securities as follows:

“On September 30, 2012, certain holders of the debentures converted the principal amount of $100,000 and accrued interest in the amount of $6,100 into 340,960 shares of the Company's Common Stock. The conversion was done by a related party representing 0.6% of the total shares then outstanding. Prior to this transaction the company had 54,593,882 shares of common stock outstanding. Included in those shares are 170,480 shares to Paris & Aliki Nikolaidis, Trustees for the John N. Hatsopoulos Family Trust for the benefit of Nia Marie Hatsopoulos and 170,480 shares to Paris & Aliki Nikolaidis, Trustees for the John N. Hatsopoulos Family Trust for the benefit of Alexander John Hatsopoulos. Such transaction was exempt from registration under Section 3(a)(9) of the Securities Act and/or under Rule 506 of Regulation D.”

Exhibits

4.

 With respect to the exhibits you are requesting confidential treatment for, please note that the publicly filed documents should be marked as indicated in Staff Legal Bulletin No. 1A, and should include a legend indicating that the material has been omitted pursuant to a request for confidential treatment and that the material has been filed separately. Please further note that any comments on your request for confidential treatment must be resolved before we will accelerate the effective date of your registration statement.

We have filed the exhibits for which confidential treatment has been requested marked as indicated in Staff Legal Bulletin No. 1A, including the required legend.

Securities and Exchange Commission

January 15, 2013

Page 3

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Mindy Hooker, Staff Accountant

Jeanne Baker, Staff Accountant

Erin Jaskot, Staff Attorney

Craig Slivka, Special Counsel

January 4 , 2013

Via E -mail
John N. Hatsopoulos
Chief Executive Officer
Tecogen , Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen  Inc.
Amendment No. 4 to Registration Statement on Form S -1
Filed December 21, 2012
  File No. 333 -178697

Dear Mr.  Hatsopoulos :

We have reviewed  your response letter and the above -referenced filing, and have the
following comments.

Management’s Discussion and Analysis of Financial Condition and Results of Operations, page
48

Results of Operations, page 52

1. We note that your selling expense has increased significantly over the periods presented.  In
this regard, we also note that as a percentage of revenues, selling expense was 2.6%, 7.1%
and 9.5% of revenues for 2010, 2011 and the nine months ended September 30, 2012.  Please
expand your disclosures to explain reasons for these increases and the nature of the costs
included in sellin g expense.

Security Ownership of Certain Beneficial Owners and Management, page 69

2. Please update your disclosure to present security ownership as of the most recent practicable
date.  See Item 403 of Regulation S -K.

Recent Sales of Unregistered Securities, page F -39

3. We n ote your disclosure in Note 3 on page F -10 that on September 30, 2012 certain holders
of the debentures converted the principal amount and accrued interest on the debentures into
shares of the company’s common stock.  Please include the disclosure required  by Item 701
of Regulation S -K with respect to this issuance of common stock, including the applicable
exemption from registration.

John N. Hatsopoulos
Tecogen , Inc.
January 4, 2013
Page 2

 Exhibits

4. With respect to the exhibits you are requesting confidential treatment for, please note that the
publicly filed d ocuments should be marked as indicated in Staff Legal Bulletin No. 1A, and
should include a legend indicating that the material has been omitted pursuant to a request for
confidential treatment and that the material has been filed separately.  Please furth er note that
any comments on your request  for confidential treatment  must be resolved before we will
accelerate the effective date of your registration statement.

As appropriate, please amend your registration statement in response to these comments.
You may wish to provide us with marked copies of the amendment to expedite our review.
Please furnish a cover letter with your amendment that keys your responses to our comments and
provides any requested information. Detailed cover letters greatly facilitate our review. Please
understand that we may have additional comments after reviewing your amendment and
responses to our comments.

You may contact Mindy Hooker , Staff Accou ntant, at 202 -551-3732, or Jeanne Baker ,
Staff Accountant , at 202 -551-3691 if you  have questions regarding comments on the financial
statements and related matters.  Please contact Erin Jaskot, Staff Attorney,  at 202-551-3442,  or
Craig Slivka , Special Counsel,  at 202-551-3729 with any other questions.

Sincerely,

 /s/ Craig E. Slivka, for

Pamela A. Long
Assistant Director

cc:   Kristen A. Young , Esq. ( via E-mail)
Sullivan & Worcester  LLP

CORRESP
1
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		TGN CORRESP S-1 2012.12.21

December 21, 2012

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Re:     Tecogen Inc.

Amendment No.3 to Registration Statement

No. 333-178697

Dear Ms. Long:

The purpose of this letter is to respond to your letter of October 16, 2012 regarding the above registration statement. For your convenience, your original comments appear in bold text, followed by our response. We are concurrently filing Amendment No. 4 to the Form S-1.

Amendment No. 4 to Registration Statement on Form S-1

Business, page 26

Tecogen’s Strategy for Growth, page 29

1.

 We note your response to comment six of our letter dated August 2, 2012. It appears that your estimate of the total growth of new CHP in the U.S., assumes that the projected penetration of new CHP in the U.S. will be the same as the projected penetration of new CHP in California. Please advise us why you believe that the growth rates will be similar and revise your disclosure accordingly.

We have revised our disclosure by modifying our analysis methodology.  The calculation for market potential was based upon the assumption that the expected market growth in California can be extrapolated to the U.S. We recognize that this assumption can be questioned on the basis that California’s growth may have local influences such as gas/electricity prices, as well as state regulations and incentives. Therefore, we now instead use the predicted U.S market growth potential of 35,000 MW by 2030, as the foundation of our analysis.  This value was already presented earlier on page 28 and was derived from the IEA report. From this total, it is necessary to determine the portion allocated to our product size range, but this level of detail is not presented in the IEA report. So instead, we reference the ICF report on the California CHP market, which does project the breakdown of the market by size range.  We make the plausible assumption that the percentage of small size CHP (50-500 kW) in California should be applicable to the U.S since this factor is a function of facility composition (i.e. hospitals, schools, hotels), which is more reasonably applied to the country as a whole. We use this percentage and

Securities and Exchange Commission

December 21, 2012

Page 2

apply it to the total US market potential to calculate the projected small size market. The remainder of the analysis methodology remains the same. We have revised our disclosure as follows:

“The Company believes that the largest number of potential new customers in the U.S. require less than 1,000 kW of electric power and less than 1,200 tons of cooling capacity. We are targeting customers in states with high electricity rates in the commercial sector, such as California, Connecticut, Massachusetts, New Hampshire, New Jersey and New York.

As stated earlier, the total US Market Potential in 2030 is projected to be 35,000 MW.  In order to estimate the share of that market in our size range, we reference a study done by ICF International on the California market that breaks down projected market penetration by kW output range.  According to Combined Heat and Power Market Assessment of the California Energy Commission (April 2010), in 2029, new CHP in the size range that fits our products (50 kW to 500 kW), is projected to be 476 MW in the base case, or 684 MW if incentives such as carbon credits and power export credits are considered.  This size range constitutes 17.4% of the total California market potential in the base case, or 11% in the case with incentives.  If we assume California’s apportionment of small size CHP is applicable to the country, we can estimate the US market addressable by our products as 17.4% of 35,000 MW in the base case (11% with incentives) which amounts to 6,100 MW (3,864 MW with incentives).  If we assume we can capture 30% of this market, the potential over the next twenty years is 11,600 – 18,300 InVerde (100 kW) units, or approximately $1.3 – 2.1 billion in revenue (@ $112,500 per unit).”

2.

 We note your response to comment nine of our letter dated August 2, 2012. Based on our review of the materials you provided to us supplementally, it appears that the title of the third column in Table 1 on page 30 should be “1-4.9” and not “1-14.9.” Please revise accordingly.

We have revised our disclosure as requested and corrected the title on the third column in Table 1 on page 30 to be “1-4.9”.

Contribution to Revenue, page 37

3.

 We note your revisions in response to comment 11 of our letter dated August 2, 2012. Please also disclose that you have sold only one Ilios water heater and have five in production in your Prospectus Summary and Business section where you discuss your products and elsewhere in your prospectus as appropriate.

We have revised our disclosure as requested to include in the Prospectus Summary and Business section that as of the date of this prospectus, we have sold one Ilios water heater and have five in production.

Securities and Exchange Commission

December 21, 2012

Page 3

*     *    *

We appreciate your comments and welcome the opportunity to discuss with you our responses provided above.  Please call me at (781) 466-6440 or our attorney, Edwin Miller of Sullivan & Worcester LLP in Boston, at (617) 338-2447 if you have any questions or require additional information.

Sincerely,

TECOGEN INC.

/s/ Bonnie J. Brown

By:    Bonnie J. Brown

Chief Financial Officer

cc:      Mindy Hooker, Staff Accountant

Jeanne Baker, Staff Accountant

Erin Jaskot, Staff Attorney

Craig Slivka, Special Counsel

October 16 , 2012

Via E -mail
John N. Hatsopoulos
Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen  Inc.
Amendment No. 3 to Registration Statement on Form S -1
Filed October 2 , 2012
  File No. 333 -178697

Dear Mr.  Hatsopoulos :

We have reviewed  your response letter and the above -referenced filing, and have the
following comments.

Amendment No. 3  to Registration Statement on Form S -1

Business, page 26

Tecogen’s Strategy for Growth, page 29

1. We note your response to comment six of our letter dated August 2, 2012.  It appears that
your estimate of the total growth of new CHP in the U.S., assumes that the projected
penetration of new CHP in the U. S. will be the same as the projected penetration of new
CHP in California.  Please advise us why you believe that the growth rates will be similar
and revise your disclosure accordingly.

2. We note your response to comment nine of our letter dated August 2,  2012.  Based on our
review of the materials you provided to us supplementally, it appears that the title of the
third column in Table 1 on page 30 should be “1 -4.9” and not “1 -14.9.”  Please revise
accordingly.

Contribution to Revenue, page 37

3. We note y our revisions in response to comment 11 of our letter dated August 2, 2012.
Please also disclose that you have sold only one Ilios water heater and have five in
production in your Prospectus Summary and Business section where you discuss your
products and  elsewhere in your prospectus as appropriate

John N. Hatsopoulos
Tecogen Inc.
October 16, 2012
Page 2

 As appropriate, please amend your registration statement in response to these comments.
You may wish to provide us with marked copies of the amendment to expedite our review.
Please furnish a cover letter with your amendment that keys your responses to our comments and
provides any requested information. Detailed cover letters greatly facilitate our review. Please
understand that we may have additional comments after reviewing your amendment and
responses to our  comments.

You may contact Mindy Hooker , Staff Accou ntant, at 202 -551-3732, or Jeanne Baker ,
Staff Accountant , at 202 -551-3691 if you  have questions regarding comments on the financial
statements and related matters.  Please contact Erin Jaskot, Staff Attorney,  at 202-551-3442,  or
Craig Slivka , Special Counsel,  at 202-551-3729 with any other questions.

Sincerely,

 /s/ Craig E. Slivka, for

Pamela A. Long
Assistant Director

cc:   Kristen A. Young , Esq. ( via E-mail)
Sullivan & Worcester  LLP

August 2,  2012

Via E -mail
John N. Hatsopoulos
Chief Executive Officer
Tecogen Inc.
45 First Avenue
Waltham, MA 02451

Re: Tecogen  Inc.
Amendment No. 2 to Registration Statement on Form  S-1
Filed July 19 , 2012
  File No. 333 -178697

Dear Mr.  Hatsopoulos :

We have reviewed  your response letter and the above -referenced filing, and have the
following comments.

Amendment No. 2  to Registration Statement on Form S -1

Risk Factors, page 6

General

1. We note your revisions in response to comment four of our letter dated May 24, 2012.
We note the following:

 It appears that in revising you risk factors you included mitigating language i n
your disclosure.  Please note that  such language should not be included in risk
factors.  For example, we note that your risk factor that you “expect significant
competition for [y]our products and services” now includes disclosure stating that
you retain a competitive advantage for most o f your products.  Please revise your
risk factors to remove such mitigating language and to clearly present the material
risk to your company.  For additional guidance, please see Staff Legal Bulletin
No. 7 (1999).

 We continue to believe that your risk fa ctors should be tailored to your business
so that investors may have a better understanding of how these risks could impact
your future results and financial condition.  For example, your risk factor noting
the significant fluctuations in revenues from per iod to period should provide a
historical example of such fluctuations.  Similarly, we note that your risk factor
on page nine discussing the effect of various regulations does not discuss the

John N. Hatsopoulos
Tecogen Inc.
August 2, 2012
Page 2

 regulatory risks that are specific to your business, as discuss ed on page 44.  In
particular, we note that your disclosure on page 44 states that you “expect to get a
CHP unit permitted in Southern California by year -end 2012,” but your risk
factors do not discuss any risks to your business if you fail to secure such a
permit.  Similarly, your risk factor regarding utility -imposed barriers on the
installation of your products suggests that utilities or government entities could
impose such barriers, but your disclosure on page 45 suggests that many of such
barriers are  already in place.  These are just examples.  Please revise your risk
factors accordingly.

Businesses and consumers might not adopt cogeneration solutions as a means for obtaining their
electricity and power needs, page 9

2. We note your response to comment  three of our letter dated May 24, 2012.  Your risk
factor continues to be drafted as if cogeneration is a new technology, which conflicts with
your disclosure elsewhere noting that you have several decades of sales of cogeneration
products.  Please revise  this risk factor to accurately refle ct the history of your business.
To the extent that the risk is that you may not be able to increase acceptance of
cogeneration beyond the market that you currently serve, please clearly state this fact.

3. We note your  revisions in response to comment  five of our letter dated May 24, 2012.
Please further revise your risk facto r to address the potential risks relating to George
Hatsopoulos  having little or no continuing stake in the company,

Business, page 26

General

4. We have reviewed the supplemental materials that you provided to us in response to
comment nine of our letter dated May 24, 2012.  We were unable to locate support for the
following statements.

 “The best efficiency obtainable today is about 50% from ei ther a combined -cycle
steam turbine or a fuel cell” (page 27);

 Table 2 – Fossil Fuel Carbon Emissions (page 32);

 Figure 4 – Comparison of Carbon Emissions (GHG) . . . (page 33);

 Figure 5 – Emission Levels of Criteria Pollutants . . . (page 34); and

 Figure 6 – Comparison of Tecogen Ultra Low -Emissions . . . (page 34).

John N. Hatsopoulos
Tecogen Inc.
August 2, 2012
Page 3

 Please supplementally  provide us with copies of the sources for each of these statements,
clearly marked to highlight the portion or section that contains the information and cross -
reference it to the appropriate location in your filing.
5. Please disclose that the data in “Fig ure 1 – Major Economies’ CHP Potential” is from
2008.

Tecogen’s Strategy for Growth, page 29

6. We note your statement on page 30 that the projected penetration of new CHP in
California by 2030 is 6.1 MW, and extrapolating this to the country as a whole, you
estimate the market addressable by your products is 40,000 MW which represents the
sales equi valent of $4.5 billion in revenue.  According to the ICF Report, 6.1 MW is
actually the “High Case” scenario, and the “Base Case” is 1.8 MW and the “Medium
Case” is 3.6 MW.  Please revise your disclosure to present a balanced discussion of the
projected pe netration of new CHP in California.  To the extent you wish to retain the
High Case, please also include the Base Case and Medium Case, including corresponding
revisions to the total market addressable and the potential revenue.  Please also tell us
how yo u determined the total market addressable for the United States from the
California data.  Finally, please clarify whether your assumption relating to potential
revenue assumes that you gain 100% of the market share that is addressable by your
product line s.  To the extent this is the case, please clarify your disclosure accordingly
with appropriately balanced disclosure that takes into account your competitive position.

7. We note your statement on page 30 stating that the largest market sectors identified b y
ICF closely match your sales data.  Please list the market sectors identified by ICF, and
supplementally provide us with supporting material for this statement.

8. We note the chart on page 30 showing your customer distribution.  The sentence
preced ing thi s chart suggests that it is your customer distribution for “several decades of
sales through 2009.”  Please advise whether this chart is rep resentative of the distribution
of customers for your recent sales.  To the extent it is not, please include a simil ar chart
showing customer distribution in the past five years.  Please  also disclose whether there
have been any significant changes in customer distribution during this time.

9. We are unable to locate supporting material for the “Current Inventory” listed in “Table 1
– CHP Market Penetration by Size in California.”  Please provide us with supporting
material for this data.  Further, we note that the chart seems to show that there is a
decrease in market penetration for systems over 20 MW from now until 2029 .  Please
advise and revise your disclosure accordingly.

John N. Hatsopoulos
Tecogen Inc.
August 2, 2012
Page 4

 Tecogen’s Solution, page 32

10. We are unable to locate the part of the ASHRAE Journal article supporting your
statement that your products can reduce operating costs by 30% to 60%.  Further, we not e
that this article does not specifically address your products, but instead addresses
cogeneration generally.  Please revise your disclosure to remove the suggestion that this
speaks to your products specifically.  We also note that this article is from O ctober 2002.
Please advise us as to whether you believe that this article is still reliable.  To the extent
that you retain disclosure relating to this article, please clearly disclose that the data is
from 2002.

Contribution to Revenue, page 37

11. It appears that you have not generated any revenue from the Ilios high -efficiency water
heaters.  However, we note that  throughout the prospectus you consistently list this water
heater  as one of your three main products.  Please advise us as to the status  of this
product, including whether there have been any sales to date.  Please revise your
disclosu re in each section in which you discuss your main products to clearly disclose the
status of sales.

Competitive Position and Business Conditions, page 40

12. It appears that the source material you have provided for “Table 3 – Comparison of CHP
Technologies to Tecogen’s InVerde 100” may have come from a source other than the
ICF Report.  Please advise and provide us with the supporting material, if different tha n
the ICF Report.  Please also provide us with a complete copy of the ICF Report.

13. Please indicate that the data in “Figure 9 – Technology Size and Market Position” is from
2004 as indicated in the ICF Report.

14. Please indicate that the data in “Figure 10 – Share of Installed CHP by Prime Mover in
California” is from 2008.

Intellectual Property, page 43

15. We note your disclosure that you do not consider any one of your patents or related group
of patents to be of such importance that their expiration, termin ation, or invalidity would
materially affect your business.  However, disclosure elsewhere in your prospectus
suggests that certain patents are material to your bu siness.  For example, on page seven
you note that given your patents and licenses, it would b e difficult for any company to
develop a product t hat competes with the  InVerde CHP unit, which you  also refer to in
the prospectus as your premier cogeneration product .  This disclosure suggests that if
such patents and licenses were to expire, your competitors could create competing

John N. Hatsopoulos
Tecogen Inc.
August 2, 2012
Page 5

 products which presumably would have a material effect on  your business.  Please further
advise as to why  you do not believe any of your patents or licenses are material.

Government Regulation and Its Effect on Our Busin ess, page 43

16. Please revise your disclosure to further explain what you mean by the statement that
“because the inverter is virtually identical to those  used in renewable power systems, its
certification will likely be preserved . . .”  Please disclose how  long you will maintain the
UL Certification, and any risks that you may lose such certification.  Please also add
disclosure in your Risk Factors secti on as appropriate.

Certain Relationships and Rel ated Party Transactions, page 75

17. Please disclose the basis on which Levitronix LLC and Alexandros Partners LLC, are
related persons.  See Item 404(d) of Regulation S -K.

18. Please disclose the approximate dollar value of the amount involved in your Facilities
and Support Services Agreement with American DG Energy.  Please also disclose the
monthly rate paid by American DG Energy for office space and utilities.

Unaudited Interim Financial Statements

19. Please revise your filing to include a statement of shareholders’ equity for the period
from  the latest fiscal year end to the interim balance sheet date.  This can be done either
as a separate statement or in a footnote to your financial statements.  Please refer to ASC
505-10-50-2 for guidance.

Note 6 – Noncontrolling Interest, page F -12

20. Please provide us the underlying calculations for the stockholders’ equity adjustments
related to the investor’s purchase of 1 million shares of Ilios for $500,000.

Consolidated Statement of Stockholders’ Equity, page F -19

21. We have read your response to prior comment 40 of our letter dated May 24, 2012.  It
appears that the quantitative assessment you provided regarding the materiality of your
error only addresses the impact of the error as it relates to the net loss attribut able to
Tecogen Inc.  Please expand your assessment to address the impact of this error on all
financial statement line items, including your balance sheet line items, which were
impacted by the error and subsequent adjustments.  This includes analysis of both the
2010 and 2011 financial statements.  Please also address how you determined that the
10% impact to your net loss attributable to Tecogen Inc. is quantitatively not material.
Finally, please address the appropriateness of correcting this error by making a

John N. Hatsopoulos
Tecogen Inc.
August 2, 2012
Page 6

 reclassification of $35,764 in 2011 “in the reallocation to noncontrolling interest resulting
from the Tecogen purchase of Ilois common stock."

Exhibit Index

22. We note that in response to certain of our comments i n our letter dated May 24, 2012 you
indicate  that you intend to request confidential treatment for various exhibi ts.  To the
extent that we have comments on yo ur request, please note that we will issue them in a
separate letter.  Please note that all comments on your request must be reso lved before we
will entertain a request to accelerate the effective date of your registration statement.

As appropriate, please amend your registration statement in response to these comments.
You may wish to provide us with marked copies of the amendment  to expedite our review.
Please furnish a cover letter with your amendment that keys your responses to our comments and
provides any requested information. Detailed cover letters greatly facilitate our review. Please
understand that we may have additional comments after reviewing your amendment and
responses to our comments.

You may contact Mindy Hooker , Staff Accou ntant, at 202 -551-3732, or Jeanne Baker ,
Staff Accountant , at 202 -551-3691 if you  have questions regarding comments on the financial
statements and related matters.  Please contact Erin Jaskot, Staff Attorney,  at 202-551-3442,  or
Craig Slivka , Special Counsel,  at 202-551-3729 with any other questions.

Sincerely,

 /s/ Craig E. Slivka, for

Pamela A. Long
Assistant Director

cc:   Kristen A. Young , Esq. ( via E-mail)
Sullivan & Worcester  LLP

May24, 2012
 Via E-mail

John N. Hatsopoulos Chief Executive Officer Tecogen Inc. 45 First Avenue Waltham, MA 02451
Re: Tecogen Inc.
Amendment No. 1 to Registrati on Statement on Form S-1
Filed April 27, 2012
  File No. 333-178697

Dear Mr. Hatsopoulos:

We have reviewed your response letter a nd the above-referenced filing, and have the
following comments.    Amendment No. 1 to Registration Statement on Form S-1

 General

1. Please revise your document to include updated financial statements in accordance with
Rule 8-08 of Regulation S-X.
2. Since you appear to qualify as an “emerging growth company,” as defined in the
Jumpstart Our Business Startups Act (“the Act”), please disclose  on your prospectus
cover page that you are an emerging growth  company, and revise your prospectus to
provide the following additional disclosures:
 Describe how and when a company may lose emerging growth company status;

 A brief description of the various exemptions that ar e available to you, such as
exemptions from Section 404(b) of the Sarbanes-Oxley Act of 2002 and Section
14A(a) and (b) of the Securities Exchange Act of 1934; and
 Your election under Secti on 107(b) of the Act:

o If you have elected to opt out
 of the extended transition period for
complying with new or revised accoun ting standards pursuant to Section
107(b) of the Act, include a statement that the election is  irrevocable; or

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 2

 If you have elected to use the extend ed transition period for complying
with new or revised accounting stan dards under Section 102(b)(2)(B) of
the Act, provide a risk factor explai ning that this election allows you to
delay the adoption of new or revi sed accounting standards that have
different effective dates for public  and private companies until those
standards apply to private companies.  Please state in your risk factor that,
as a result of this election, your financial statements may not be comparable to companies that comply with public company effective dates.  Include a similar statemen t in your critical accounting policy
disclosures in MD&A.
 Risk Factors, page 6

3. We note your response to comment 11 of our letter dated January 18, 2012.  However,
we continue to believe that to the extent th at there are certain risks facing your company
that are similar to early-stage companies, please tailor such risks so that they apply
specifically to the circumstances of your comp any.  For example, your risk stating that
businesses and consumers might not adopt  cogeneration should discuss whether
businesses have adopted such technology in the last several decades th at you have offered
such technology.  Further, to the extent the risks relate to newly introduced technology,
such as your new Ultra-low emissions technol ogy, the risk factors should clearly state
this fact.  Please note that these are just examples.  Please comprehensively revise your risk factors to ensure that each of them reflects the current state of your business and
explains the specific risk as applied to th e specific facts and circumstances of your
company.  For additional guidance, pleas e see Staff Legal Bulletin No. 7 (1999).

4. We note your response to comment 12 of our letter dated January 18, 2012.  However, it
does not appear that you have revi sed your risk factors so that they cite specific examples
of how the risks have imp acted your business so that investors may have a better
understanding of how these risks could impact your future results and financial condition.
As one example, we note that your risk factors on page 11 relating to changes in
regulation and barriers to entry into the market place state that  certain regulations, fees or
restrictions may be imposed.  However, we note your extensive discussion of the specific
impact of various regulations on pages 47 – 51, including that you developed your Ultra-
low emissions technology in response to cert ain regulations in S outhern California.
Please note that this is just one example.  Please comprehens ively review and revise your
risk factors to tailor each risk factor so that  it addresses the specific  risks that impact your
business and presents such risks in a clear and concise manner.

5. We note your response to comment 14 of our le tter dated January 18, 2012.  We continue
to believe that you need to include a risk f actor addressing the poten tial risks relating to
John and George Hatsopoulos having little or  no continuing stake in the company, and
revise your risk factor on page 15 stati ng that you are controlled by a small group of
majority stockholders to reflect the fact that these stockholders have registered for resale

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 3

 100% of their holdings.  It is unclear from your response why there is  “essentially no risk
that John and George Hatsopoulos will sell a ll of their holdings.”  Given that the
shareholders are registering all of their holdings for resale, in  the event that the
registration statement is declared effective, th e shareholders would be able to sell all of
their holdings.  Please note, the amount bei ng registered for resale  must reflect a good
faith estimate of the amount that the selling s ecurity holders intend to sell.  To the extent
that John and George Hatsopoulos do not in tend to sell 100% of their holdings, please
revise accordingly.  Please advise.

Selling Security Holders, page 16

6. We note that in response to comment 15 of  our letter dated January 18, 2012 you state
that you have revised your disclosure to incl ude how the selling security holders acquired
the securities they may offer and sell pursuant to the registration statement, including the
dates of the transactions, the number of shar es purchased in each  transaction, and the
purchase price, if any.  However, we are unable to locate such disclosu re in this section.
Please advise and revise accordingly.
7. We note that in response to comment one  of our letter date d January 18, 2012 you
included an “Exhibit A” which you state lists each selling security holder, including the
number of shares registered on behalf of that shareholder on the S-1.  However, it is
unclear from Exhibit A and the disclosure provided on pages 19-21 which of the shares
listed in Exhibit A are being registered for resale.  For example, Exhibit A notes that
there are 303,223 shares owned by George Ha tsopoulos that are issuable upon future
exercise of a convertible debenture, but it is unclear whether Mr. Hatsopoulos is
attempting to register such shares for resale.  Please advise which of the shares listed in
Exhibit A are being registered, and ensure that your disclosure in this section accurately
reflects the shares being registered by each selling security holder.

Business, page 24

General

8. Please provide support for your statement on page 31 that “no other methodology for
obtaining this level of efficien cy gain exists or will ever  exist from power generation
sourced from fossil fuels.”  To the extent th at this statement is based on management’s
belief, please indicate that this is the case.  Alternatively, if the information is based on reports or articles, please provide  support for your statement.

9. Please provide us with copies of each source that supports your va rious qualitative and
quantitative statements in your disclosure, clearly marked to highlight the portion or
section that contains this information and cros s-reference it to the appropriate location in
your filing, as requested in comment 18 of our letter dated January 18, 2012.

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 4

 10. Please revise your disclosure here and in your  Prospectus Summary to clarify what you
mean by a low-cost “process of engine after treatment.”
11. We note your disclosure on page 24 that your principal generator suppliers are Danotek
Motion Technologies and Mara thon Electric, that you purch ase compressors from J&E
Hall International, and, as noted on page 30, you use a Ford engine for the Ilios heat
pump.  Please file agreements with these suppliers as exhibits to the registration
statement, or tell us why you are not required to do so.

12. We note you responses to comments 18 and 19 of our letter date d January 18, 2012, and
that you wish to keep certain footnotes in the Background section.  Further, we note that
you have significantly expanded your disc ussion under the Industry background section
and Business section so that you now include additional footnotes in your disclosure and
both these footnotes and the main text cont ain lengthy disclosure that includes highly
technical terms.  Please note th at your disclosure should co mply with the Plain English
requirements of Rule 421 of Regulation C.  Please delete the foot notes and revise your
disclosure throughout so that you avoid jargon and highly tec hnical terms and present the
relevant information in a clea r and concise manner.  For example, it does not appear that
detailed descriptions, such as the diffe rence between HHV and LHV, or a detailed
description of a permanent magnet synchronous generator, are helpful to an investor.
These are just examples and you should recons ider and revise the Business and Industry
sections in their entirety. Further, please de lete the references to external websites that
you include throughout your regist ration statement.  By including the URL or website
addresses, the information contained in the webs ite is treated as part  of the disclosure.
See
 SEC Release No. 33-7856 and SEC Releas e No. 33-7497 for additional guidance.

13. We note that in response to comment 23 of  our letter dated January 18, 2012, you have
indicated that you do not believe that your  business is dependent on American DG
Energy.  However, we note the significant am ount of your sales to American DG Energy
in 2010 and 2011, as disclosed in Note 13 to th e financial statements, and the fact that
you have entered into various agreements w ith American DG Energy indicating that you
will continue to do a notable amount of busine ss with American DG Energy in the future.
Based on your relationship with American  DG Energy, it is unclear why you do not
believe that you will have recurring revenue from American DG Energy.  Please advise.

Industry Background, page 25

Our Products and Services, page 30

14. We note your response to comment 27 of our letter dated January 18, 2012.  Given the
emphasis placed on each of your three products, we believe it is important for investors to
understand the contribution to revenues made  by each of your products.  Please revise
your disclosure accordingly.

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 5

 15. We note your disclosure on page 42 that you ha ve used the results of certain tests to
obtain an air permit exemption in New Jerse y.  Please revise your disclosure here, and
elsewhere as appropriate, to  explain why such a permit was required and whether you
will need similar permits to sell your products in other states or regions.

Distribution Methods, page 34

16. Please file any material agreements with distributors and outs ide sales agents and
representatives as exhibits to the registration statement.

17. We note that American DG Energy has exclusive sales representation rights to certain of
your products in New England, and that you pay a commission to American DG Energy
when you sell such products in New England.  Please disclose the amount of such commission, to the extent material, as we ll as any material impacts on your financial
operations.
18. Please disclose the purpose and or/intent of American DG Energy’s grant of sales
representation rights to its On-Site Utility en ergy service in Californi a.  In particular,
please explain what this energy se rvice is and what you intend to  use it for.  Please revise
your disclosure elsewhere, as appropriate.

Market Potential, page 35

Tecogen’s Strategy for Growth, page 38

19. Please revise or delete your disclosure thr oughout this section to eliminate repetitive,
highly technical and speculative disclosure.  The current disclosure is overly detailed,
complex and unclear.  To the extent that you wish to retain disclosure regarding the
market potential of CHP, please present it cl early and concisely, and consider including it
within another section of your prospe ctus, such as the Industry section.

Alliances, page 41

20. We note your revised disclosure in response to comment 32 of our letter dated January
18, 2012.  Please further revise you r disclosure to disclose th e dates of such alliances,
whether these are current alliances, and the sign ificance of such alliances.  Further, we
note that you state that you believe that “m ost” of these agreements are not material.
Please advise us as to which agreements are ma terial and please file such agreements as
exhibits to the registration statement.
21. We note your response to comment 33 of our letter dated January 18, 2012 that you do
not believe your exclusive licensing agreem ent with Wisconsin Alumni Research
Foundation is material because it “provide s for a $500 payment to the Foundation every
time [you] sell an InVerde system.”  It is un clear why this means that the agreement is

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 6

 not material.  In addition, we note that this  agreement covers the control software that
enables your microgrid system and allows your  products to be inte grated, and it appears
that the microgrid system is an important pa rt of your products.  Please file a copy of
your exclusive licensing agreem ent with the Wisconsin Alumni Research Foundation as
an exhibit to the registration statement or, alternatively, please explain why this
agreement is not material, including why a $500 payment for each InVerde system means
the agreement is not material.  See
 Item 601(b)(10) of Regulation S-K.

Competition, page 42

22. We note that your disclosure regarding your competitive position is overly detailed and
complex and it is unclear how some of the disc losure is relevant to  your company.  Please
comprehensively revise this section to pres ent a clear and concise description of the
competitive business conditions and your competitive position in the industry.

Certain Related Party Contracts, page 46

The Company and Its Affiliates, page 47

23. The disclosure contained in th ese sections appears to be dup licative of the disclosure in
the section entitled “Certain Relationships and Related Transactions.”  Please delete this
disclosure and consolidate your disclosure  under “Certain Relationships and Related
Transactions.”
Intellectual Property, page 47

24. Please disclose the duration of  your patents and licences.

Government Regulation, page 47

25. We note that your disclosure regarding your competitive position is overly detailed and
complex.  Further, we note that some of this disclosure appears to be phrased as a commentary on the industry standards, includ ing a historical overview, as opposed to a
concise description of the eff ects of government regulations.  For example, we note your
statement that “[t]he imposition of se emingly unreasonable standards by the SCAQMD
was not without warning nor arbi trary….”   Please comprehensiv ely revise this section to
present a clear and concise desc ription of the existing or pr obable effects of government
regulations on your business.  See
 Item 101(h)(4)(ix) of Regulation S-K.

John N. Hatsopoulos Tecogen Inc. May24, 2012 Page 7

 Management’s Discussion and Analysis of Financ ial Condition and Results of Operations, page
55

26. We note your revisions in res ponse to comment 47 of our letter dated January 18, 2012.
However, we note that your Overview section continues to appear to be largely identical
to the disclosure in your Prospectus Su mmary and in your Business section.  Your
MD&A Overview section should provide c ontext for the remainder of

January 18, 2012
 Via E-mail

John N. Hatsopoulos Chief Executive Officer Tecogen Inc. 45 First Avenue Waltham, MA 02451
Re: Tecogen Inc.
Registration Statement on Form S-1 Filed December 22, 2011
  File No. 333-178697

Dear Mr. Hatsopoulos:

We have reviewed your registration statem ent and have the following comments.  In
some of our comments, we may ask you to provi de us with information so we may better
understand your disclosure.
 Please respond to this letter by amending your registration statement and providing the
requested information.  If you do not believe  our comments apply to your facts and
circumstances or do not believe an amendment is appropriate, please tell us why in your
response.
 After reviewing any amendment to your re gistration statement and the information you
provide in response to these comments, we may have additional comments.
 Registration Statement on Form S-1

 General

1. We note that you are proposing to register the resale of up to 35,381,768 shares of your
common stock on behalf of certain selling stockholders listed in the registration
statement.  Given the size of this offering relative to the number of outstanding shares
held by non-affiliates, as well as the nature of  the selling stockholders, we believe this
transaction might be a primary offering.  Pleas e provide us with your analysis as to why
this offering is a secondary offering under Rule  415(a)(1)(i) and not an indirect primary
offering for which the selling stockholders should  be identified as underwriters.  In your
analysis, you may wish to  address the following fact ors: how long the selling
stockholders have held the securities, the ci rcumstances under which they received them,
their relationship to the registrant, the amount  of securities involve d, whether they are in
the business of underwriting securities, and fi nally, whether under all the circumstances it

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 2

 appears that they are acting as a conduit for the company.  Please refer to Question
612.09 of the Division’s Compliance & Disclosu re Interpretations for Securities Act
Rules.
 Prospectus Cover Page

2. We note your statement that the selling stockhol ders do not include any of your directors,
officers or 10% holders and the prospectus ma y not be used by any such person or entity.
Given that John N. Hatsopoulos  and George N. Hatsopoulos  are selling stockholders,
please delete this statement.
 Table of Contents

3. Please remove the last sentence of the third paragraph on the prospe ctus cover page and
the last two sentences of the first paragraph under the table of contents.  These statements
may suggest to investors that you are not re sponsible for omissions of material facts
necessary to make your statements  not misleading at the time of sale or contract of sale.
Information that is conveyed afte r the time of sale or contract  of sale is not taken into
account for purposes of section 12(a)(2) or  17(a)(2) of the Se curities Act.  See  Securities
Act Rule 159.
Prospectus Summary, page 1

4. Please ensure that your summary is balance d.  Please disclose up front that you have
incurred operating losses for your prior fiscal  years, including quantifying the number of
years that you have had such losses, and th at you expect you will continue to incur such
losses.
5. We note certain statements regarding the be nefits of your CHP pr oducts, including that
such products decrease greenhouse gas emissions and that you have a proven track record of reliability in commercial CHP systems.  Please provide additional disclosure supporting such statements, including how your products reduce greenhouse gas
emissions (or, if, alternatively, these system s have lower emissions than other competing
products) and examples of your proven track record.
6. We note your disclosure on page 10 that your internal controls ove r financial reporting
were not effective as of September 30, 2011. Pl ease prominently disclose this in your
Summary section.

7. We note your disclosure on page 59 that John N. Hatsopoulos, your CEO, spends only
approximately 20% of his business time on th e affairs of the company.  Please disclose
this fact in your Summary section.

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 3

 8. We note that you conduct a notable amount of  business and other transactions with
certain “affiliated companies,” and that a number of members of management and the
Board also have positions with such affiliated companies.  Please provide an overview of your relationship with such affiliated companies in your Summary section.
 Risk Factors, page 4

 General

9. We note in the introductory paragraph to your  risk factors secti on you state that there
may be risks that you do not consider materi al now but may become material, or there
may be risks that you have not yet identified. You must disclose all risks that you believe
are material at this time. Delete this language from your  introductory paragraph.

10. We note that many of your risk  factors are currently written as if you are an early stage
company without any significant operating history.  For exam ple, we note that you state
that you may not be successful in executing your business plan, that you expect
competition for your products and services, a nd that businesses and consumers might not
adopt cogeneration solutions as a means for obt aining their power need s.  These are just
examples. However, we note that your co mpany has actually been operating since the
early 1960’s, and some members of management have been with the company since the
sale of Tecogen in 2000, or prio r thereto.  Please comprehensiv ely revise your risk factors
to ensure that each of them reflects the cu rrent state of your business and explains the
specific risk as applied to the specific facts and circum stances of your company.

11. In general, risk factors that  describe circumstances that could apply equally to other
businesses that are similarly situated are gene ric risks that should not  be included in your
risk factor section. For example, we note that  the following risk factors appear to contain
generic disclosure:

 Our success is dependent upon attracting and retaining highly qualified personnel
. . .,(page 6);

 We may make acquisitions th at could harm our financial performance, (page 9);

 Our ability to access capital for the repayment of debts . . ., (page 9);

 Our quarterly operating results are subject  to fluctuations . . ., (page 9); and

These are just examples. Please either eliminat e these generic risks, or revise them to
state the specific material ri sks that apply to you or to th e purchasers in this offering.

12. We note that your risk factors often cite a specific risk wit hout providing any examples of
how that risk has specifically impacted your business so that investors may have a better

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 4

 understanding of how this risk could imp act your future operations and financial
condition.  We note the following examples:
 The execution of our growth strategy is dependent upon the continued availability
of third-party financing . . ., page 4;

 We are dependent on third-part y suppliers . . ., page 5;

 Business and consumers might not adopt cogeneration solutions as a means for
obtaining their electricity and power needs, page 6;

 We operate in a highly regulated bu siness environment . . ., page 7;

 Utility companies or governmental entities could place barriers to our entry into
the marketplace . . ., page 7;

 Commodity market factors impact our costs . . ., page 8;

 Our products involve a lengthy sales cycle and we may not anticipate sales levels
appropriately . . ., page 8;

 The economic viability of our projects de pends on the price spread between fuel
and electricity . . ., page 8; and

 We are exposed to credit risks with respect to some of our customers (page 9).
 These are just examples.  Please revise accordingly.
 We may be unable to fund our future  operating requirements . . ., page 4

13. Please revise this risk factor to address whether your curren t funds are sufficient to fund
your operating requirements.
 We are controlled by a small group of majority stockholders…, page 10

14. Please reconcile this risk f actor with the fact that Ge orge and John Hotsopoulos are
seeking to sell 100% of their holdings and in clude a risk factor addressing the potential
risks related to these individua ls having little or no contin uing stake in the company.
 Selling Security Holders, page 14

15. Please disclose how the selling security hol ders acquired the securities they may offer
and sell pursuant to the registration statement,  including the dates of the transactions, the
number of shares purchased in each tr ansaction, and the purch ase price, if any.

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 5

 Legal Matters, page 21

16. We note that the disclosure under the h eading “Legal Matters ” relates to legal
proceedings.  It is unclear why this disclosure  has been included in this section.  Please
revise to advise who will opine on the valid ity of the common stock offered pursuant to
the registration statement.
 Business, page 22

 General

17. We note your disclosure that the company wa s formed in the early 1960s, and was then
sold to private investors in 2000.  Howeve r, your disclosure throughout the business
section and the prospectus does not, at times, seem consistent with a company that has
been in operation for an extended period of time.   Please revise your disclosure to provide
investors with a better unde rstanding of the general de velopment of your business,
including, for example, how long you have sold  your current products  and whether there
have been any significant changes in the focu s of your business since its establishment in
the 1960s.  Please also disclose whether you r company was known as Tecogen prior to
2000, or was instead a part of Thermo El ectron at that time.  Please make any
corresponding changes to the Summary section as well.

18. We note that your disclosure includes various  qualitative and compar ative statements and
that for certain of these statements, you ha ve provided footnotes citing the sources of
such information.  Please delete  these footnotes and instead indicate in the text of your
disclosure both the name and date of the source for the various statements.  Finally,
please tell us whether you commissioned the re port or any part thereof and, if so, please
either file consents or explai n to us why you are not required  to do so under Rule 436 of
Regulation C and Section 7 of the Securities Ac t.  To expedite our review, please provide
us with copies of each source, clearly mark ed to highlight the portion or section that
contains this information and cross-reference it  to the appropriate loca tion in your filing.

19. Please disclose whether you are attempting to  incorporate the information on external
web sites into this prospectus.  Please s ee our Use of Electronic Media, Interpretive
Release No. 33–7856 (Apr. 28, 2000) for further gui dance regarding the use of hyperlinks
in your prospectus.
20. We note that you provide data relating to the e fficiency of the electr icity industry and the
prospective CHP market in various sectors, in cluding an estimate of  market potential, but
this data is from 2000 and 2004.  If you wish to provide this sort of data to investors,
please ensure that it takes into account more recent developments.  The disclosure should
not include data that has since changed or is no longer accurate given developments in
the industry in the past decade.  Please revise accordingly.

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 6

 21. We note your use of industry and product sp ecific jargon throughout this section.  For
example, you use the terms “UL-certifie d,” “inverter,” “conv entional induction
generators,” and “permanent-magnet generato r.”  Please revise to provide context for
these terms so an investor not familiar w ith your industry can understand such terms.

22. Please revise your disclosure  to include the following:

 The sources and availability of raw materials, and the names of principal
suppliers; and

 An estimate of the amount spent during each of the last two fiscal years on
research and development activities, and if applicable, the extent to which the cost
of such activities is born e directly by customers.
 See
 Item 101(h)(4) of Regulation S-K.

23. Please include a discussion of your dependen ce on one or a few major customers. We
note in particular the disclosure in Note 13 to  the financials on pa ge F-36 that you receive
a significant portion of your revenues from  sales to American DG Energy Inc.  See  Item
101(h)(4)(vi) of Regulation S-K.
 Industry Background, page 23

24. Please provide illustrative support and context for certain of the statements that you make
in this section.  For example, please provide  additional disclosure as to how many large
industrial plants have ad opted CHP technology, and what you mean by “large” when
referring to such plants.  This is only an example.

25. We note the list of reasons why CHP acceptance in the commercial sector is increasing.
Please explain why these reasons increase CH P acceptance.  For example, you state that
CHP systems reduce pollutants more “easily, ch eaply and quickly” but it is unclear what
other systems you are comparing the CHP sy stems to in making such a comparison.
Please also clarify who you are referring to in your statement regarding the pressure to
cut “their” operating costs.  Further, it appe ars that this disclosu re should appear under
“Tecogen’s solution” as opposed to “Industry Background.”
26. We note your reference throughout this section to “grid congestion” and to “rigorous air
quality rules.”  Please provide a brief overview of the specifics of th e air quality rules and
grid congestion in the Industry Background section.
 Our Products and Services, page 24

27. Please revise your disclosure to explain the markets for each of your products and, to the
extent material to an underst anding of your business, please disclose the contribution to

John N. Hatsopoulos Tecogen Inc. January 18, 2012 Page 7

 your revenues made by each of these products.  Please also provide context so that an
investor may understand the extent of time th at you have sold each of these products and
the effect of each of these products  on your overall financial condition.

28. Please revise your disclosure to describe th e distribution methods of your products.  See

Item 101(h)(4)(ii) of Regulation S-K.
29. We note your statement that you have “recen tly” developed an advanced technology for
controlling engine emissions in conjuncti on with the California Energy Commission and
the Southern California Gas Company.  Pl ease disclose what you mean by recently.
Please also advise whether, other than with re gard to the sale of units to the Sacramento
Municipal Utility District in Californ ia in mid-2011, you have entered into any
agreements relating to the Ultra emission control produc t, including its sale or
development.  Please also file any such ag reements as exhibits to the registration
statement.  See
 Item 601(b)(10) of Regulation S-K.

30. We note that the engine used in your cogene ration modules and chil lers is supplied by
General Motors.  Please disc losure whether you purchase such motors pursuant to a
supply agreement with General Motors, or othe rwise.  Please also file any such supply
agreement or similar agreement as an exhibit to the registration statement.  See  Item
601(b)(10) of Regulation S-K.

31.  We note your disclosure on page 25 th at your cogeneration products offer many
compelling advantages, such as lower cost, better  quality control, higher reliability, etc.
Please revise your disclosure to specify thos e product