EXHIBIT 99.1

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                       AS ADOPTED PURSUANT TO SECTION 906
                        OF THE SARBANES-OXLEY ACT OF 2002


            In connection with the Quarterly Report on Form 10-Q for the period
ending March 31, 2003 of Comfort Systems USA, Inc. (the "Company") as filed with
the Securities and Exchange Commission on the date hereof (the "Report"), I,
William F. Murdy, Chairman of the Board and Chief Executive Officer of the
Company, certify that, to my knowledge, (i) the Report fully complies with the
requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934,
as amended, and (ii) the information contained in the Report fairly presents, in
all material respects, the financial condition and results of operations of the
Company.


                                                   /s/ William F. Murdy
                                                   -----------------------------
                                                   William F. Murdy
                                                   Chairman of the Board and
                                                   Chief Executive Officer
                                                   (Principal Executive Officer)


May 5, 2003