April 27, 2012

Via EDGAR

Pamela A. Long, Assistant Director

Securities and Exchange Commission

Division of Corporation Finance

100 F Street, NE

Washington, DC 20549

Dear Ms. Long:

The purpose of this letter is to respond to your letter of January 18, 2012 regarding the Form S-1. 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.

Registration Statement on Form S-1

General

We do not believe that the Company is engaged in a primary offering of securities based on the financing history and other circumstances relating to the Company.

Full details about the financing history of the Company are set forth in tabular form below attached as Exhibit A. Briefly, the Company or its predecessors was established in the early 1960s. Certain of the shareholders purchased the Company from their former employer, Thermo Electron Corporation (which is now Thermo Fisher Scientific Inc.) in 2000. Since the acquisition date, the Company has engaged in various financings, all to accredited investors known personally by the Company’s management. None of the non-affiliates who hold only unrestricted stock are named as selling stockholders. The selling stockholders consist of: (i) non-affiliated purchasers who purchased the Company’s equity within the last year, and so are still subject to certain provisions of Rule 144, (ii) several executive officers and directors who own a small number of shares; and (iii) two affiliates of the Company, namely John N. Hatsopoulos and his brother, George N. Hatsopoulos who were the founders of the Company in 2000.

Tecogen Inc.

45 First Avenue

Waltham, MA 02451

781-466-6400 • 781-466-6466 (fax)

www.tecogen.com

Non-Affiliates. The non-affiliates who purchased shares within the last year did not have any registration rights, and because they were unable to sell shares without restriction for a year, we do not see how they can be considered conduits for the Company, making this offering a primary offering. The purpose of the registration statement is to put all shareholders on a “level playing field” with those shareholders who are able to sell on an unrestricted basis. In addition, the availability of those shares for sale will provide additional depth for the trading market for the Company’s shares that the Company hopes to establish.

The only issuances by the Company of equity securities, other than in connection with its founding over 10 years ago, were several customary private placements since inception in the ordinary course of business, and the Company is voluntarily seeking liquidity for its shareholders, many of whom have been involved with the Company for many years. A significant majority of the shares held by affiliates, founders George N. and John N. Hatsopoulos have been held for nearly twelve years. The most recent purchase by affiliates was by George N. Hatsopoulos on September 24, 2011 in a Section 3(a)(9) exchange, whereby he requested that accrued interest on the convertible debenture issued on September 24, 2001, in the amount of $12,948, be converted into the Company’s common stock at $0.50 per share (which was the average price of the Company’s stock from September 24, 2001 to September 24, 2011). We emphasize that at the time of the private placements, not only was the Company private, but there was no trading market for the Company’s shares and there was no contractual commitment to register the privately placed shares or plan to create a trading market. Under those circumstances, it is difficult to see how the purchasers were purchasing with a view to distribution. We respectfully submit that on these facts our registration is in no way a primary offering of securities.

Affiliates. The issue relating to affiliates is more complex. Although the general consensus is that all executive officers and directors are affiliates, we believe in our circumstances that the only affiliates of the Company are John N. Hatsopoulos and possibly George N. Hatsopoulos. John N. Hatsopoulos was responsible for the original acquisition, has continuously been the Company’s chief executive officer since then, and beneficially owns 27.4% of the Company’s common stock. Although George N. Hatsopoulos owns a significant amount of shares and is a member of the Company’s board of directors, he is in ill health and, under no reasonable meaning of the word, does George N. Hatsopoulos control the Company.

We fully understand the SEC’s policy underlying its comment about a public offering. We understand that this policy is based on the SEC’s view of the need for investor protection in reverse mergers and similar transactions where affiliates attempt to sell securities to a public that has not had enough time to analyze the newly public information about the Company. We also understand the necessity of investor protection in our circumstances – that affiliates should not be able to sell securities until public information has been available for a sufficient period of time. If it would satisfy the staff’s concerns, John N. and George N. Hatsopoulos would be willing to sign a lock-up agreement with the Company not to sell any securities under the prospectus for a reasonably period of time after effectiveness (we suggest 90 days). We would disclose this arrangement on the cover of the prospectus, and the Company would agree not to waive it other than in the cases of death or disability. We would appreciate an opportunity to discuss this proposal directly with the staff.

At the end of this response letter we have presented in tabular form a list of each selling shareholder of the Company, showing separately for each shareholder each transaction in which that shareholder acquired Company securities; the number of shares registered on behalf of that shareholder on the S-1; and, in notes, any relationship of that shareholder to the Company or with another shareholder and any broker-dealer affiliations of the selling shareholders (see Exhibit A).

Prospectus Cover Page

We have revised our disclosure as requested and removed this statement.

Table of Contents

We have revised our disclosure as requested and removed those statements.

Prospectus Summary, page 1

We have revised our disclosure as requested to disclose that we have incurred operating losses for our prior fiscal years, including quantifying the number of years that we have had such losses, and that we expect that we will continue to incur such losses.

We have revised our disclosure as requested to include a detailed description that supports the statements we make in the Prospectus Summary page. That description can be found in the Business, Tecogen’s Solution section on page 27 and in the Business, Ultra Low-Emissions Technology section on page 32. In those sections we describe the reliability of our CHP systems and that the reliability surpasses typical power plants. We also disclose that the Ultra low-emissions technology was developed in 2010 as part of a funded research effort sponsored by the California Energy Commission and Southern California Gas Company.

We have revised our disclosure as requested to disclose in our Summary section that our internal controls over financial reporting were not effective as of December 31, 2011.

We have revised our disclosure as requested to disclose in our Summary section that John N. Hatsopoulos, our CEO, spends only approximately 20% of his business time on the affairs of the Company.

We have revised our disclosure as requested to include the following in our Prospectus Summary section:

“Tecogen has three affiliated companies, namely American DG Energy, EuroSite Power and GlenRose Instruments. These companies are affiliates because several of the major stockholders of those companies, have a significant ownership position in the Company. American DG Energy, EuroSite Power and GlenRose Instruments do not own any shares of the Company, and the Company does not own any shares of American DG Energy, EuroSite Power or GlenRose Instruments. The common stockholders include John N. Hatsopoulos, the Company’s Chief Executive Officer who is the Chairman of GlenRose Instruments, the Chief Executive Officer of American DG Energy and a director of EuroSite Power. Also, Dr. George N. Hatsopoulos, who is John N. Hatsopoulos’ brother, is a director of the Company, is the Chairman of American DG Energy and an investor in GlenRose Instruments. The business of GlenRose Instruments is not related to the business of the Company, American DG Energy and their other corporate affiliates.”

Risk Factors, page 4

General

We have revised our disclosure as requested to remove this language from the introductory paragraph.

We note that we are still a very small Company and that a number of our technologies are new and innovative. Hence we believe that the risk factors for the Company in many ways are the same as early stage companies. Nevertheless, we have revised a number of disclosures to address the issues raised by the Staff.

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

We are uncomfortable in removing risk factors that we believe appear in the vast majority of technology Company prospectuses. These risk factors, to a large extent, are common to technology companies and/or small businesses, but are not necessarily common to multiple non-technology businesses or to larger businesses. We note, as applicable, that the risk factors arise as a result of the Company being a small technology company, and we have added disclosure where applicable to more specifically describe the risk as it relates to the Company.

These are just examples. Please revise accordingly.

Similarly to the last comment, we believe that these risk factors are relevant generally in assessing an investment in a small technology Company. Indeed, these risks may not have specifically impacted the Company but are risks that may well affect our business in the future. We have revised the risk factors to more specifically deal with the risks described in the context of being a small technology Company.

We may be unable to fund our future operating requirements…, page 4

We have revised our disclosure as requested to include the following:

“To the extent that our funds are insufficient to fund our future operating requirements, we would need to raise additional funds, through further public or private equity or debt financings depending upon prevailing market conditions. These financings may not be available, or if available, may be on terms that are not favorable to us and could result in dilution to our stockholders and reduction of the trading price of our stock. The state of worldwide capital markets could also impede our ability to raise additional capital on favorable terms or at all. If adequate capital were not available to us, we likely would be required to significantly curtail our operations or possibly even cease our operations. We believe that our existing resources, including cash and cash equivalents and future cash flows from operations, are sufficient to meet the working capital requirements of our existing business until March 31, 2013. Beyond March 31, 2013, as we continue to grow our business our cash requirements may increase. We may need to raise additional capital through a debt financing or an equity offering to meet our operating and capital needs for future growth.”

We are controlled by a small group of majority stockholders…, page 10

Respectfully, we do not believe that this revision is necessary. There is essentially no risk that John and George Hatsopoulos will sell all of their holdings. First, the market would not support such sales in large volumes. The only circumstance where this could take place would be in a block transaction and the only circumstance where a block transaction is in any way likely to occur is in the event of death or disability. We advise the Staff that the shares of George and John Hatsopoulos are being registered in substantial part for the purposes of tax and estate planning. Tax and estate planning are particularly important for George Hatsopoulos because of his ill health. We note also that John Hatsopoulos is 78 years old. This risk factor is meant to alert the public that he will have reduced influence over the Company because of the concentrated holdings. If, because of death or disability, a significant number of these shares are sold in a block transaction, the risk would continue to apply. Further the Company would be uncomfortable in suggesting that John and George Hatsopoulos would continue to be actively involved in the business, having sold their shares. That circumstance would be hard to imagine.

Selling Security Holders, page 14

We have revised our disclosure to include the information requested.

Legal Matters, page 21

We have revised our disclosure as requested to include that the validity of our Common Stock offered under this prospectus will be passed upon by Sullivan & Worcester LLP, Boston, Massachusetts.

Business, page 22

General

We have revised our disclosure in the Prospectus Summary section and Business section as requested to include the following:

“Tecogen was formed in the early 1960’s as the Research and Development New Business Center of Thermo Electron Corporation, (which is now Thermo Fisher Scientific Inc.). For the next 20 years, this group performed fundamental and applied research in many energy-related fields to develop new technologies. During the late 1970’s, new federal legislation enabled electricity customers to sell power back to their utility. Thermo Electron Corporation saw a fit between the technology and know-how it possessed and the market for cogeneration systems. In 1982, the Research and Development group released its first major product, a 60-kW cogenerator. In the late 1980’s and early 1990’s, air-conditioning and refrigeration products using the same gas engine-driven technology were introduced, beginning with a 150-ton chiller. In 1987, Tecogen was spun out as a separate entity by Thermo Electron Corporation and in 1992 Tecogen became a division of the newly formed Thermo Power Corporation. In 2000, Thermo Power Corporation was dissolved, and Tecogen was sold to private investors including Thermo Electron Corporation’s original founders, Dr. George N. Hatsopoulos and John N. Hatsopoulos.”

We respectfully request that we keep certain footnotes in the Business section as they are an integral part of our presentation and make the flow of our business concepts easier to the reader. Where possible, we have transferred substance to the text. We confirm that we have not commissioned any report or any part thereof.

Copies of these sources will be provided to the Commission under separate cover.

We are not trying to incorporate information from external websites into the prospectus. In the prospectus we state on the cover page and again on page 25, “The information on, or that may be accessed through, our website is not incorporated by reference into this prospectus and should not be considered a part of this prospectus.” We have revised our disclosure to make clear that the websites of others are not incorporated by reference.

We have revised our disclosure as requested to include recent reports regarding market potential and other related information.

We have revised our disclosure as requested to include context for these terms as requested.

See Item 101(h)(4) of Regulation S-K.

We have revised our disclosure on the Business, Overview section on page 24 as requested to include the following:

“Our principal engine supplier is GM and principal generator suppliers are Danotek Motion Technologies and Marathon Electric. To produce air-conditioning, our engines drive a compressor purchased from J&E Hall International.”

We have revised our disclosure on the Business, Tecogen’s Strategy for Growth section on page 38 as requested to include the following:

“Our efforts to forge partnerships continue to focus on utilities, particularly to promote the InVerde, our most utility-friendly product. The nature of these alliances vary by utility, but could include simplified interconnection, joint marketing, ownership options, peak demand mitigation agreements, and customer services.  We are currently installing a microgrid with SMUD at its headquarters in Sacramento California, where the central plant will incorporate three InVerde modules equipped with our Ultra low-emissions technology. A portion of the expenses for this project are being reimbursed to SMUD through a grant from the California Energy Commission.”

We have revised our disclosure on the Business, Tecogen’s Strategy for Growth section on page 38 as requested to include the following:

“We also continue to leverage our resources with government and industry funding, which has yielded a number of successful developments. These include the Ultra low-emissions technology, which was sponsored by the California Energy Commission and Southern California Gas Company. Currently, we are testing the durability of a new engine technology that we developed with the California Energy Commission’s support.  If tests succeed, the engine could be applied in smaller CHP systems such as a 35-kW InVerde unit and in new, ultra-high-efficiency heating and air-conditioning products. For the years ended December 31, 2011 and 2010, we spent $223,745 and $763,990, respectively, in research and development activities all of which was reimbursed through grants from the California Energy Commission and Consortium for Electric Reliability Technology Solutions.”

We have revised our disclosure on the Business, Overview section on pages 3, 25 and 57 as requested to include the following paragraph:

“Although we may, from time to time, have one or a few customers who may represent more than 10% of our product revenue for a given year, we are not dependent on the recurrence of such revenue from those customers. Our product revenue is such that customers may make a large purchase once and may not likely ever make such a purchase again. Our equipment is built to last 20 or more years; therefore, we do not build our product revenue model depending on recurring transactions from the same customer. Our service revenue may lend itself to recurring revenue from a single customer; however, we currently do not have any service revenue customers who make up more than 10% of our total revenues on an annual basis. American DG Energy has been considered a major customer in certain years as disclosed in the accompanying financial statements, however, we do not consider our business as “dependent” upon its recurrence.”

Industry Background, page 23

We have revised the Business section of our disclosure in its entirety to include additional information about our operations so an investor not familiar with our industry can understand such terms. The above reference has been deleted.

We have revised the Business section of our disclosure in its entirety to include additional information about our operations so an investor not familiar with our industry can understand such terms. The above reference has been deleted.

The above reference has been deleted, however, further detail can be found under sections Business, Industry Background, and Business, Tecogen’s Strategy for Growth.

Our Products and Services, page 24

We have provided disclosure on the contribution to our revenues made by each of our products as an answer to comment 81 as requested. We have also included the extent of time that we have sold each of these products as an answer to comment 17.

We have also revised our disclosure on the Business, Our Products and Services, InVerde section on page 30 as requested to include that the InVerde CHP system was developed in 2007 and begun shipping in 2008.

We have revised our disclosure on the Business, Our Products and Services section on page 34 as requested to include the following:

“Distribution methods

Our products are sold directly to end-users by our sales team and by established sales agents and representatives. Various agreements are in place with distributors and outside sales representatives, who are compensated by commissions, including three affiliated companies, for certain territories and product lines. For example, we have sales representatives for the chiller market in the New York City/New Jersey territory; however, we do not have a sales representative for our cogeneration products in this territory. Sales sold through our in-house sales team or for those sales that are not covered by a sales representative’s territory, are sold without commission or with a fractional commission amount.

American DG Energy has sales representation rights to our products and services. In New England, American DG Energy has exclusive sales representation rights to our cogeneration products not including chillers. When Tecogen sells its cogeneration products in New England, a commission is paid to American DG Energy. American DG Energy has granted us sales representation rights to its On-Site Utility energy service in California, however, as of the date of this registration statement, this agreement has not materialized into any significant revenues. American DG Energy also has exclusive rights to our Ultra low-emissions technology if it is applied to engines from other CHP manufacturers used for their specific energy projects. In other words, American DG Energy could purchase CHP products from suppliers other than us and license that supplier to incorporate our Ultra low-emissions technology as long as the CHP system is owned and operated American DG Energy.”

We have revised our disclosure on the Business, Tecogen’s Solution section in the first paragraph on page 29 as requested, to include that the Ultra low-emissions technology was developed in 2010 as part of a funded research effort sponsored by the California Energy Commission and Southern California Gas Company. We have also disclosed that since then we have sold Ultra systems to various customers. We do not believe that any one of these agreements is material and required to be filed as exhibits.

We have revised our disclosure as requested to include that our engines and certain other parts for our cogeneration and chillers systems are purchased directly from General Motors pursuant to a supply agreement between Tecogen and General Motors. We will file those supply agreements as exhibits to the registration statement, and request confidential treatment for such exhibits.

We have revised our disclosure on the Business, Our Products and Services, Summary of advantages of our products section on page 34 (2^nd bullet point) as requested to include the following:

“Our CHP products are all standard, modular units that come pre-packaged from the factory to simplify installation and grid connection. The systems are supported in the field by a nationwide network of experienced professional staff. Standardized CHP units offer many compelling advantages, including lower cost, better quality control, higher reliability, easier service, integrated emission controls, and complete system warranty and maintenance support, than custom CHP systems.”

Alliances and Partnerships, page 27

Our use of the word “partnership” was not meant to mean a separate partnership entity. We have revised our disclosure as requested and changed the title on page 41 to “Alliances” and disclosed the nature of those relationships. We will file any material agreements as exhibits to the registration statement as requested; however we believe that most of those agreements are not material therefore is not required to be filed as exhibits.

The Wisconsin Alumni Research Foundation licensing agreement provides for a $500 payment to the Foundation every time we sell an InVerde system. We therefore do not believe that the agreement is material and required to be filed as an exhibit.

Competition, page 28

We have revised our disclosure on the Business, Tecogen’s Strategy for Growth section on page 42 (last paragraph) as requested, to include the following description:

“A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more reciprocating pistons to convert pressure into a rotating motion.”

We have revised the Business, Competition section of our disclosure on page 41 in its entirety to include additional information about our competition so an investor not familiar with our industry can better understand our competitive landscape.

We have revised the Business, Competition section of our disclosure on page 41 in its entirety to include additional information about our competition so an investor not familiar with our industry can better understand our competitive landscape. The above reference has been deleted.

We have revised the Business, Competition section of our disclosure on page 41 in its entirety to include additional information about our competition so an investor not familiar with our industry can better understand our competitive landscape. The above reference has been deleted.

Certain Related Party Contracts, page 29

We have revised the Certain Related Party Contracts disclosure on page 46 as follows:

“American DG Energy has sales representation rights to our products and services. In New England, American DG Energy has exclusive sales representation rights to our cogeneration products not including chillers. When Tecogen sells its cogeneration products in New England, Tecogen pays a commission to American DG Energy. American DG Energy has granted us sales representation rights to its On-Site Utility energy service in California; however, as of the date of this registration statement, this agreement has not materialized into any significant revenues. American DG Energy also has exclusive rights to our Ultra low-emissions technology if it is applied to engines from other CHP manufacturers used for their specific energy projects. In other words, American DG Energy could purchase CHP products from suppliers other than us and license that supplier to incorporate our Ultra low-emissions technology as long as the CHP system is owned and operated American DG Energy.”

On October 20, 2009, American DG Energy, in the ordinary course of its business, signed a Sales Representative Agreement with Ilios to promote, sell and service the Ilios high-efficiency heating products, such as the high efficiency water heater, in the marketing territory of the New England States, including Connecticut, Rhode Island, Massachusetts, New Hampshire, Vermont, and Maine. The marketing territory also includes all of the nations in the European Union. Since the Ilios high-efficiency heating products are relatively new and the market acceptance is currently unknown, we do not believe that this agreement is material and required to be filed as an exhibit.

The Company and its Affiliates, page 29

We have revised The Company and its Affiliates disclosure on page 47 as follows:

“We have three affiliated companies: (a) American DG Energy, a publicly traded Company that distributes, owns and operates on-site energy systems that produce electricity, hot water, heat and cooling in the United States, (b) EuroSite Power, a publicly registered Company that distributes, owns and operates on-site energy systems that produce electricity, hot water, heat and cooling in the United Kingdom and Europe, and (c) GlenRose Instruments, a Company that provides radiological services, operates a radiochemistry laboratory network and provides radiological characterization and analysis, hazardous, radioactive and mixed waste management, facility, environmental, safety, and industrial hygiene health management.

These three companies are affiliates because several of the major stockholders of those companies, have a significant ownership position in the Company. American DG Energy, EuroSite Power and GlenRose Instruments do not own any shares of the Company, and the Company does not own any shares of American DG Energy, EuroSite Power or GlenRose Instruments. The common stockholders include John N. Hatsopoulos, the Company’s Chief Executive Officer who is the Chairman of GlenRose Instruments, the Chief Executive Officer of American DG Energy and a director of EuroSite Power. Also, Dr. George N. Hatsopoulos, who is John N. Hatsopoulos’ brother, is a director of the Company, the Chairman of American DG Energy and an investor in GlenRose Instruments. The business of GlenRose Instruments is not related to the business of the Company, American DG Energy and their other corporate affiliates.”

We have revised our disclosure as follows:

“We currently own a 62.5% interest in Ilios. American DG Energy and EuroSite Power purchase the majority of their energy equipment from Tecogen. The primary types of equipment used are natural gas engine-driven cogeneration and air conditioning systems provided by Tecogen and ultra-high-efficiency heating products, including a high efficiency water heater from Ilios. Both Tecogen and American DG Energy distribute the Ilios products.”

Government Regulations, page 30

We have revised the Government Regulations section of our disclosure on page 47 in its entirety to include additional information about government regulations so an investor not familiar with our industry can better understand our business.

Employees, page 30

We have revised our disclosure as follows:

“As of the date of this prospectus, we employed 56 active full-time employees and four part-time employees. We believe that our relationship with our employees is satisfactory. None of our employees are represented by a collective bargaining agreement; however, a few of our New Jersey and New York City service employees have been in contact with a labor union and we are currently negotiating with this labor union.”

Properties, page 30

We will revise our disclosure as requested and file the lease for our headquarters in Waltham, Massachusetts as an exhibit.

Market for Common Equity and Related Stockholder Matters, page 31

Rule 144, page 31

We will revise our disclosure as follows:

“Rule 144

In general, pursuant to Rule 144, under the Securities Act, as currently in effect, once we have been subject to the reporting requirements of Section 13 or 15(d) of the Exchange Act for 90 days, a person (or persons whose shares are aggregated) who is not deemed to have been an affiliate of ours at any time during the three months preceding a sale, and who has beneficially owned restricted securities within the meaning of Rule 144 for a least six months (including certain periods of consecutive ownership of preceding non-affiliated holders) would be entitled to sell those shares, subject only to the availability of current public information about us. Under Rule 144, a person who is not deemed to have been one of our affiliates at any time during the 3 months preceding a sale, and who has beneficially owned the shares proposed to be sold for at least one year is entitled to sell the shares without complying with the public information, manner of sale, volume limitation or notice provisions of Rule 144.

In general, under Rule 144 as currently in effect, once we have been subject to the Exchange Act reporting requirements for 90 days, our affiliates or persons selling shares on behalf of our affiliates who own shares that were acquired from us or an affiliate of ours at least six months prior to the proposed sale are entitled to sell within any three-month period beginning 90 days after the date of this prospectus, a number of shares that does not exceed the greater of:

Sales under Rule 144 by our affiliates or persons selling shares on behalf of our affiliates are also subject to certain manner of sale provisions and notice requirements and to the availability of current public information about us.”

We will revise our disclosure of Outstanding Common Stock as requested to include the following:

“Under the unlimited resale provisions of Rule 144, there are 15,635,046 shares of our Common Stock eligible for resale under Rule 144 without any additional holding period.”

Management’s Discussion and Analysis of Financial Condition and Results of Operations, page 34

We will revise our disclosure as requested and add the following paragraph following the Overview section in our Management Discussion and Analysis disclosure:

“For the last twelve months, the majority of our revenue was generated from long-term maintenance contracts, or service contracts, which provide us with a somewhat predictable revenue stream, especially during the summer months. We have a slight surge of activity from May through September as our “chiller season” is in full swing. Our service margins are generally predictable as we service hundreds of long-term contracts.

Our product revenue is derived from the sale of the various cogeneration modules, such as the InVerde 100, the CM-75 and the CM-60, and the three chiller models, such as the smaller ST, the larger DT and the RT (roof-top) units. The sales cycle for each product varies widely, whereby it can be as short as a month to as long as a year or more, depending on the number of decision makers in our customer’s facility. Furthermore, since our products and their installation are costly they are considered a major capital improvement and customers may be slow in making their buy decision. Therefore our product revenue can be difficult to predict and the expected margin, which is based on the various models we offer, also varies therefore it is also difficult to forecast.

Our cogeneration and chiller units are built to order and revenue is recognized upon shipment. The time to build a unit depends on its customized configuration and is approximately 12 to 16 weeks, so our work-in-process is an important factor in understanding our financial condition at any given quarter.”

Results of Operations, page 39

Nine Months Ended September 30, 2011 Compared to Nine Months Ended September 30, 2010, page 39

Revenues, page 39

We have revised our disclosure to include results of operations for the year ended December 31, 2011 compared to year ended December 31, 2010. We have expanded our disclosure to address your comment.

We have expanded our disclosure to address your comment.

We have revised our disclosure as requested and revised this statement.

Cost of Sales, page 39

We have expanded our disclosure to address your comment.

We have expanded our disclosure to address your comment.

We have expanded our disclosure to address your comment.

Year Ended December 31, 2010 Compared to Year Ended December 31, 2009, page 40

Revenues, page 40

We have expanded our disclosure to address your comment.

We have revised our disclosure to address your comment.

Cost of Sales, page 40

We have revised our disclosure to address your comment.

Operating Expenses, page 40

We have revised the Business, Distribution Methods section of our disclosure on page 34 to include discussion on commissions and commissionable sales.

Liquidity and Capital Resources, page 41

Seasonality, page 41

We have revised our disclosure as requested as follows:

“We expect that the majority of our heating systems sales will be in the winter and the majority of our chilling systems sales will be in the summer. Our cogeneration and chiller system sales are not generally affected by the seasons, although customer goals will be to have chillers installed and running in the spring. Our service team does experience higher demand in the warmer months when cooling is required. These units are generally shut down in the winter and started up again in the spring. This “busy season” for the service team generally runs from April/May through the end of September.”

Changes in and Disagreements with Accountants on Accounting and Financial Disclosure, page 42

We have revised our disclosure to include the following:

“On April 13, 2011, Caturano and Company, Inc. (formerly Caturano and Company, P.C.), or Caturano, resigned as the Company’s independent registered public accounting firm as a result of the July 20, 2010, acquisition by McGladrey & Pullen, LLP, or McGladrey, of certain of Caturano’s assets. The Company’s board of directors appointed McGladrey as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2010. 

Caturano’s audit reports on the Company’s financial statements for the fiscal years ended December 31, 2009 and December 31, 2008 did not contain any adverse opinion or disclaimer of opinion, and were not qualified or modified as to uncertainty, audit scope or accounting principles. During the Company’s fiscal years ended December 31, 2009 and December 31, 2008 and through the date of Caturano’s resignation, there were no disagreements between the Company and Caturano on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which disagreements, if not resolved to Caturano’s satisfaction, would have caused Caturano to make reference thereto in connection with its audit reports, and no reportable events as defined in Item 304(a)(1)(v) of Regulation S-K.

Prior to the engagement of McGladrey, we did not consult with such firm regarding the application of accounting principles to a specific completed or contemplated transaction, or any matter that was either the subject of a disagreement or a reportable event. We also did not consult with McGladrey regarding the type of audit opinion that might be rendered on our financial statements and no oral or written report was provided by McGladrey.”

Inflation, page 42

The rise in the general level of prices of goods and services in an economy over a period of time affects all companies in an economy, but does not affect the Company more than others. Therefore, we will remove the disclosure on inflation as it does not have any significant impact on our business.

Quantitative and Qualitative Disclosures About Market Risk, page 42

We have revised our disclosure to remove the reference on our exposure to market risk.

Management and Governance, page 43

We have revised our disclosure under Management and Governance, as requested, to include the following:

“John N. Hatsopoulos is the Company’s Chief Executive Officer and is also the Chief Executive Officer of American DG Energy and the Chairman of GlenRose Instruments. On average, Mr. Hatsopoulos spends approximately 20% of his business time on the affairs of the Company; however such amount varies widely depending on the needs of the business and is expected to increase as the business of the Company develops.”

We have revised our disclosure as requested to include that Charles T. Maxwell is currently Senior Analyst with Weeden and Co. of Greenwich, Connecticut since 1999.

We have revised our disclosure as requested as follows:

“Mr. Loumidis is currently the Chief Financial Officer of the Company’s affiliates, American DG Energy since 2004, EuroSite Power since 2010, and GlenRose Instruments since 2006.”

Board Committees, page 46

We will revise our disclosure and will renumber our Exhibits, such that our Audit Committee Charter will now be Exhibit No. 99.1, our Compensation Committee Charter will now be Exhibit No. 99.2, and the Nominating and Governance Committee Charter will now be Exhibit No. 99.3.

Director Compensation, page 47

We have revised our disclosure as follows:

“Each director who is not also one of our employees will receive a fee of $500 per day for service on those days that our Board of Directors and-or each of the Audit, Compensation or Nominating and Governance Committees hold meetings, or otherwise conduct business. Non-employee directors also will be eligible to receive stock or options awards under our 2011 Stock Incentive Plan, as amended, or the Stock Plan. We reimburse all of our non-employee directors for reasonable travel and other expenses incurred in attending Board of Directors and committee meetings. Any director who is also one of our employees receives no additional compensation for serving as a director. Our non-employee directors did not receive any compensation in cash in 2011 or 2010 because prior to filing this registration statement the compensation of directors was only in stock awards.”

We will provide an Outstanding Equity Awards at Fiscal Year-End Table for the outstanding equity awards held by each of your directors.

Executive Officer and Director Compensation, page 48

We have revised our disclosure to include information for the year ended December 31, 2011.

Summary Compensation Table, page 48

We have revised our disclosure as requested and annotated the “Option awards ($)” column in our Summary Compensation Table as follows:

The amounts in the “Stock Option Awards” column reflect the aggregate grant date fair value of the awards computed in accordance with FASB ASC Topic 718. The assumptions used by us with respect to the valuation of stock and option awards are set forth in Note 10 to our financial statements included elsewhere in this registration statement.

Outstanding Equity Awards at Fiscal-Year End, page 50

We have revised our disclosure to provide an Outstanding Equity Awards at Fiscal Year-End Table for the outstanding equity awards held by each of your directors.

Compensation Committee Interlocks and Insider Participation, page 53

The service of John N. Hatsopoulos as the director and CEO of American DG Energy is not considered a compensation committee interlock. We have revised our disclosure and removed that reference.

Certain Relationships and Related Party Transactions, page 58

We have revised our disclosure as follows:

“The Company has three affiliated companies, namely American DG Energy, EuroSite Power and GlenRose Instruments. These companies are affiliates because several of the major stockholders of those companies, have a significant ownership position in the Company. American DG Energy, EuroSite Power and GlenRose Instruments do not own any shares of the Company, and the Company does not own any shares of American DG Energy, EuroSite Power or GlenRose Instruments. The business of GlenRose Instruments is not related to the business of the Company, American DG Energy and their other corporate affiliates.

American DG Energy, EuroSite Power and GlenRose Instruments are affiliated companies by virtue of common ownership. The common stockholders include:

We have revised our disclosure and added the following paragraph:

“Additionally, the following related persons had or may have a direct or indirect material interest in our transactions with our affiliated companies:

The details of the Facilities and Support Services Agreement with American DG Energy are confidential and we will submit a confidential treatment request for that agreement.

We have revised our disclosure to include the following:

“Additional disclosure on the Company’s debt is set forth in Note 7 – Demand notes payable and convertible debentures – related party to our financial statements included in our registration statement.”

We will revise our Certain Relationships and Related Transactions disclosure as follows:

“American DG Energy has sales representation rights to the Company’s products and services in New England, and the Company has sales representation rights to the American DG Energy On-Site Utility solution in California. Revenue from sales of cogeneration and chiller systems, parts and service to American DG Energy during the years ended December 31, 2011 and 2010 amounted to $713,267 and $1,658,471, respectively.”

We will also revise our Certain Relationships and Related Transactions disclosure as follows:

“The Company subleases portions of its corporate offices and manufacturing facility to sub-tenants, several of which are affiliated companies, under annual sublease agreements. For the years ended December 31, 2011 and 2010, the Company received $185,596 and $196,466, respectively, from American DG Energy, Levitronix LLC and Alexandros Partners LLC. In addition, for the years ended December 31, 2011 and 2010, the Company received from the same affiliated companies, $224,700 and $142,050, respectively, to offset common operating expenses incurred in the administration and maintenance of its corporate office and warehouse facility.”

We will file all material related party agreements as requested.

Condensed Consolidated Statements of Cash Flows, page F-5

We have revised our disclosure as requested.

Report of Independent Registered Accounting Firm, page F-19

We have revised our disclosure to present periods ended December 31, 2011 and 2010. The Caturano and Company, Inc. audit report presents the period ended December 31, 2009, therefore, we will not include it in our registration statement.

Consolidated Statements of Shareholders’ Equity, page F-22

Ilios was formed on April 20, 2009, and became a wholly owned subsidiary of Tecogen on May 4, 2009, when Tecogen acquired 8,400,000 shares of Ilios common stock, par value $0.001. There were no Tecogen assets and /or operations transferred to Ilios on that date. On May 4, 2009, the Ilios Board of Directors was formed and the management team was appointed, therefore, considerable value was created and the Ilios Board determined that the value of the Ilios common stock had increased to $0.10. The Ilios Board authorized the issuance of 360,000 shares of restricted stock and 300,000 shares of stock options to Ilios directors, employees and consultants with an exercise price of $0.10 per share.

On May 11, 2009, after the Ilios Board reviewed the Ilios business plan that was put together by the new management team and after evaluating the potential of the new high-efficiency water heater and its market potential, it authorized a private placement of Ilios common stock at $0.50 per share.

On May 11, 2009, Tecogen had outstanding notes payable to George N. Hatsopoulos and John N. Hatsopoulos in excess of $700,000. On that date the Tecogen Board of Directors authorized the sale of 1,400,000 shares of Ilios common stock at $0.50 per share (of the 8,400,000 shares of Ilios common stock Tecogen had already owned), to George N. Hatsopoulos and John N. Hatsopoulos in exchange for $700,000 of notes payable to Tecogen. The Company viewed the debt repayment and the sale of Ilios stock as two separate arms-length transactions and appropriately accounted for the sale of the Ilios stock. Based on the fact that the extinguishment was between related parties we considered the transactions was a capital transaction and the amounts were recorded to common stock and additional paid in capital.

On July 24, 2009, Ilios raised $1,352,500 in a private placement transaction of 2,710,000 shares of common stock at a price of $0.50 per share. The private placement was done exclusively by eighteen accredited investors. Such transactions were exempt from registration under Section 4(2) of the Securities Act and/or under Rule 506 of Regulation D.

As required by FASB 470-50-40:
 

40-1 As indicated in paragraph 470-50-15-4: the general guidance for the extinguishment of liabilities is contained in Subtopic 405-20: and defines transactions that the debtor shall recognize as an extinguishment of a liability.

40-2 A difference between the reacquisition price and the net carrying amount of the extinguished debt shall be recognized currently in income of the period of extinguishment as losses or gains and identified as a separate item. Gains and losses shall not be amortized to future periods. If upon extinguishment of debt the parties also exchange unstated (or stated) rights or privileges, the portion of the consideration exchanged allocable to such unstated (or stated) rights or privileges shall be given appropriate accounting recognition. Moreover, extinguishment transactions between related entities may be in essence capital transactions.

40-3 In an early extinguishment of debt through exchange for common or preferred stock, the reacquisition price of the extinguished debt shall be determined by the value of the common or preferred stock issued or the value of the debt—whichever is more clearly evident.

The carrying amount of Ilios’ equity prior to the July 2009 private placement was $8,400.

On December 31, 2009, Tecogen held 7,000,000 of Ilios commons stock, George N. Hatsopoulos and John N. Hatsopoulos held 1,400,000 shares of Ilios common stock, and eighteen accredited investors held 2,710,000 shares of Ilios common stock that were issued on the July 2009 private placement transaction. The Ilios total shares issued and outstanding as of December 31, 2009, were 11,110,000 of which Tecogen owned 7,000,000 shares of common stock or 63.0% (not including the unvested restricted stock outstanding). There were no changes in the Ilios equity ownership during the year ended December 31, 2010.

Our noncontrolling interest calculation for December 31, 2009 was as follows:

2009 Ilios loss = $300,634 x 37% = $111,234 (the initial calculation in which $117,161 was recorded was incorrectly using the unvested restricted stock outstanding as a percentage of noncontrolling interest). The difference was not considered material to the 2009 financial statements.

2010 Ilios loss = $467,324 x 37% = $172,909 (based on an incorrect calculation we recorded $208,673 loss in noncontrolling interest in 2010). However, we made a reclassification of $35,764 in 2011 in the reallocation to noncontrolling interest resulting from the Tecogen purchase of Ilios common stock. The Company does not believe that the reclassification was material to the 2010 financial statements.

The authoritative literature used to determine the amount of net proceeds to be allocated to additional paid in capital of Tecogen and noncontrolling interest was FASB Accounting Standards Codification paragraphs 810-10-45-22 through 24 and implementation guidance provided by the following examples in 810-10-55:

55-4D  Subsidiary A has 10,000 shares of common stock outstanding. Of those shares, 9,000 are owned by its parent, Entity ABC, and 1,000 are owned by other shareholders (a noncontrolling interest in Subsidiary A). The carrying amount of Subsidiary A’s equity is $300,000. Of that amount, $270,000 is attributable to Entity ABC, and $30,000 is a noncontrolling interest in Subsidiary A. Subsidiary A issues 2,000 previously unissued shares to a third party for $120,000 in cash, reducing Entity ABCs ownership interest in Subsidiary A from 90 percent to 75 percent (9,000 shares owned by Entity ABC÷ 12,000 issued shares).

55-4E  Even though the percentage of Entity ABC’s ownership interest in Subsidiary A is reduced when Subsidiary A issues shares to the third party, Entity ABC’s investment in Subsidiary A increases to $315,000, calculated as 75 percent of Subsidiary A’s equity of $420,000 ($300,000 + $120,000). Therefore, Entity ABC recognizes a $45,000 increase in its investment in Subsidiary A ($315,000– $270,000) and a corresponding increase in its additional paid-in capital (that is, the additional paid-in capital attributable to Entity ABC). In addition, the noncontrolling interest is increased to $105,000, calculated as 25 percent of $420,000. If the parent is an NFP, the $45,000 increase in additional paid-in capital in this example is recognized instead as an increase in net assets, generally of the unrestricted class. Example 1 (see paragraphs 958-810-55-17 through 55-25) provides additional guidance for NFPs.

A description of equity transactions in 2009 related to the newly formed corporation, Ilios is discussed above, in the first bullet to comment 79. Tecogen owns a controlling interest in Ilios. Following are a list of accounting entries for the related transactions.

On May 4, 2009 Tecogen invested $8,400 in exchange for 8,400,000 ($0.001 par value) shares of a newly established corporation Ilios. The investment gave Tecogen a controlling financial interest in Ilios whose business focus will be on advanced heating systems for commercial and industrial applications.

On May 11, 2009, Tecogen sold 1,400,000 shares of Ilios common stock at $0.50 per share to George N. Hatsopoulos and John N. Hatsopoulos in exchange for the extinguishment of $700,000 in (related party) demand notes payable.

On July 24, 2009 Ilios raised $1,352,500 in a private placement by selling 2,710,000 shares of Ilios stock at $0.50 per share. After that transaction Tecogen owned a 63.0% interest in Ilios.

A summary of the transactions between Tecogen and Ilios in 2009 is as follows:

There were no equity transactions in the year ended December 31, 2010, therefore, the ownership percentage remained unchanged. However, the amount originally allocated to additional paid-in capital of Tecogen was $853,735 and the amount originally allocated to noncontrolling interest was $502,665. We do not believe the differences are material to our financial statements.

We will revise our disclosure and add the following to the footnotes to the consolidated financial statements for the years ended December 31, 2011 and 2010, respectively:

As of December 31, 2010 Tecogen owned 63.0% of Ilios. During the year ended December 31, 2011 Tecogen purchased 1,500,000 shares of Ilios common stock at $0.50 per share for an aggregate amount of $750,000 which increased Tecogen’s ownership interest to 67.4%. The table below presents the changes in equity resulting from net loss attributable to Tecogen and transfers to or from noncontrolling interests for the years ended December 31, 2011 and 2010.

Net loss Attributable to Tecogen Inc. and

Transfers (to) from the Noncontrolling Interest

Years ended December 31,

Notes to Audited Consolidated Financial Statements, page F-24

The Company reports segment data based on the management approach. The management approach designates the internal reporting that is used by management for making operating and investment decisions and evaluating performance as the source of the Company's reportable segments. The Company uses one measurement of profitability and does not disaggregate its business for internal reporting. The Company has determined that it operates in one business segment which manufactures and supports highly efficient CHP products based on engines fueled by natural gas.

The following table summarizes net revenue by product line and services:

Recent Sales of Unregistered Securities, page II-3

We have revised our disclosure of Recent Sales of Unregistered Securities to include all of the information required by Item 701 of Regulation S-K for each transaction

Undertakings, page II-5

We have revised our disclosure to include the undertaking in Item 512(a)(1)(iii) of Regulation S-K.

We have revised our disclosure and removed the undertaking in Item 512(a)(6) of Regulation S-K.

Exhibit Index

We will attach as Exhibit 5.1 the opinion of Sullivan & Worcester LLP.

We will submit our own request for confidential treatment for the Facilities, Support Services and Business Agreement between American DG Energy and Tecogen.

In connection with responding to your comments, we acknowledge that:

* * *

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 in Boston, at (617) 338-2447 if you have any questions or require additional information.

Exhibit A