<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:ns2="http://www.sec.gov/edgar/common">
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        <submissionType>144</submissionType>
        <filerInfo>
            <filer>
                <filerCredentials>
                    <cik>0001448240</cik>
                    <ccc>XXXXXXXX</ccc>
                </filerCredentials>
            </filer>
            <liveTestFlag>LIVE</liveTestFlag>



        </filerInfo>
    </headerData>
    <formData>
        <issuerInfo>
            <issuerCik>0001035983</issuerCik>
            <issuerName>COMFORT SYSTEMS USA INC.</issuerName>
            <secFileNumber>001-13011</secFileNumber>
            <issuerAddress>
                <ns2:street1>675 Bring Drive</ns2:street1>
                <ns2:street2>Suite 400</ns2:street2>
                <ns2:city>Houston</ns2:city>
                <ns2:stateOrCountry>TX</ns2:stateOrCountry>
                <ns2:zipCode>77057</ns2:zipCode>
            </issuerAddress>
            <issuerContactPhone>713-830-9600</issuerContactPhone>
            <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>BRIAN E LANE</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
            <relationshipsToIssuer>
                <relationshipToIssuer>Officer</relationshipToIssuer>
                <relationshipToIssuer>Director</relationshipToIssuer>
            </relationshipsToIssuer>
        </issuerInfo>
        <securitiesInformation>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <brokerOrMarketmakerDetails>
                <name>Morgan Stanley Smith Barney LLC Executive Financial Services</name>
                <address>
                    <ns2:street1>1 New York Plaza</ns2:street1>
                    <ns2:street2>8th Floor</ns2:street2>
                    <ns2:city>New York</ns2:city>
                    <ns2:stateOrCountry>NY</ns2:stateOrCountry>
                    <ns2:zipCode>10004</ns2:zipCode>
                </address>
            </brokerOrMarketmakerDetails>
            <noOfUnitsSold>15000</noOfUnitsSold>
            <aggregateMarketValue>6474874.50</aggregateMarketValue>
            <noOfUnitsOutstanding>35274843</noOfUnitsOutstanding>
            <approxSaleDate>05/07/2025</approxSaleDate>
            <securitiesExchangeName>NYSE</securitiesExchangeName>
        </securitiesInformation>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>04/01/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Compensation for Past Services</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>8444</amountOfSecuritiesAcquired>
            <paymentDate>04/01/2024</paymentDate>
            <natureOfPayment>Compensation</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>04/02/2018</acquiredDate>
            <natureOfAcquisitionTransaction>Compensation for Past Services</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>1046</amountOfSecuritiesAcquired>
            <paymentDate>04/02/2018</paymentDate>
            <natureOfPayment>Compensation</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>03/20/2024</acquiredDate>
            <natureOfAcquisitionTransaction>Compensation for Past Services</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>4584</amountOfSecuritiesAcquired>
            <paymentDate>03/20/2024</paymentDate>
            <natureOfPayment>Compensation</natureOfPayment>
        </securitiesToBeSold>
        <securitiesToBeSold>
            <securitiesClassTitle>Common</securitiesClassTitle>
            <acquiredDate>03/07/2018</acquiredDate>
            <natureOfAcquisitionTransaction>Compensation for Past Services</natureOfAcquisitionTransaction>
            <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
            <isGiftTransaction>N</isGiftTransaction>
            <amountOfSecuritiesAcquired>926</amountOfSecuritiesAcquired>
            <paymentDate>03/07/2018</paymentDate>
            <natureOfPayment>Compensation</natureOfPayment>
        </securitiesToBeSold>
        <nothingToReportFlagOnSecuritiesSoldInPast3Months>Y</nothingToReportFlagOnSecuritiesSoldInPast3Months>
        <noticeSignature>
            <noticeDate>05/07/2025</noticeDate>
            <planAdoptionDates/>
            <signature>/s/ Brian E Lane</signature>
        </noticeSignature>
    </formData>
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144
0001448240
XXXXXXXX
LIVE
0001035983
COMFORT SYSTEMS USA INC.
001-13011
675 Bring Drive
Suite 400
Houston
TX
77057
713-830-9600
BRIAN E LANE
Officer
Director
Common
Morgan Stanley Smith Barney LLC Executive Financial Services
1 New York Plaza
8th Floor
New York
NY
10004
15000
6474874.50
35274843
05/07/2025
NYSE
Common
04/01/2024
Compensation for Past Services
Issuer
N
8444
04/01/2024
Compensation
Common
04/02/2018
Compensation for Past Services
Issuer
N
1046
04/02/2018
Compensation
Common
03/20/2024
Compensation for Past Services
Issuer
N
4584
03/20/2024
Compensation
Common
03/07/2018
Compensation for Past Services
Issuer
N
926
03/07/2018
Compensation
Y
05/07/2025
/s/ Brian E Lane