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Table of Contents ( Mark One ) No □ ☐ UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington , D.C. 20549 Form 10 - K ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the fiscal year ended December 31 , 2020 OR TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the transition period from Delaware ( State or Other Jurisdiction of Incorporation or Organization ) Commission file number : 1-13011 Comfort Systems USA , Inc. ( Exact name of registrant as specified in its charter ) 4,938,186 ) . to 675 Bering Drive Suite 400 Securities registered pursuant to Section 12 ( b ) of the Act : 76-0526487 ( I.R.S. Employer Identification No. ) Houston , Texas 77057 ( 713 ) 830-9600 ( Address and telephone number of Principal Executive Offices ) Title of Each Class Common Stock , $ .01 par value FIX Securities registered pursuant to Section 12 ( g ) of the Act : None Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . Yes Trading Symbol ( s ) Name of Each Exchange on which Registered New York Stock Exchange Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Act . Yes No Indicate by check mark whether the registrant ( 1 ) has filed all reports required to be filed by Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 during the preceding 12 months ( or for such shorter period that the registrant was required to file such reports ) , and ( 2 ) has been subject to such filing requirements for the past 90 days . Yes No Indicate by check mark whether the registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S - T ( § 232.405 of this chapter ) during the preceding 12 months ( or for such shorter period that the registrant was required to submit such files ) . Yes No Indicate by check mark whether the registrant is a large accelerated filer , an accelerated filer , a non - accelerated filer , a smaller reporting company , or an emerging growth company . See the definitions of " large accelerated filer , " " accelerated filer , " " smaller reporting company , " and " emerging growth company ” in Rule 12b - 2 of the Exchange Act . Large accelerated filer = Accelerated filer Non - accelerated filer Smaller reporting company Emerging growth company If an emerging growth company , indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13 ( a ) of the Exchange Act . Indicate by check mark whether the registrant has filed a report on and attestation to its management's assessment of the effectiveness of its internal control over financial reporting under Section 404 ( b ) of the Sarbanes - Oxley Act ( 15 U.S.C. 7262 ( b ) ) by the registered public accounting firm that prepared or issued its audit report . » Indicate by check mark whether the registrant is a shell company ( as defined in Rule 12b - 2 of the Act ) . Yes No The aggregate market value of the voting stock held by non - affiliates of the registrant at June 30 , 2020 was approximately $ 1.45 billion , based on the $ 40.75 last sale price of the registrant's common stock on the New York Stock Exchange on June 30 , 2020 . As of February 19 , 2021 , 36,185,179 shares of the registrant's common stock were outstanding ( excluding treasury shares of