EXHIBIT 99.1 CERTIFICATION PURSUANT TO SECTION 1350, CHAPTER 63 OF TITLE 18, UNITED STATES CODE, AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 Pursuant to Section 1350, Chapter 63 of Title 18, United States Code, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, the undersigned, as chief executive officer of Comfort Systems USA, Inc. (the "Company"), does hereby certify that: 1) the Company's Quarterly Report pursuant to Section 13 or 15 (D) of the Securities Exchange Act Of 1934 (Form 10-Q) for the quarter ended June 30, 2002 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and 2) the information contained in the Company's Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of the Company. By: /s/ William F. Murdy ------------------------ William F. Murdy Chairman of the Board and Chief Executive Officer Dated: August 13, 2002