| Harrelson Mechanical Contractors Inc. | Wilmington | NC | Subcontractor |
| Harring Fire Protection LLC | Hammonton | NJ | Subcontractor |
| Harris Las Vegas LLC | Las Vegas | NV | $0 |
| Harris Mechanical, Inc. | Juliette | GA | $0 |
| Harrison-orr Air Conditioning, L.L.C | Oklahoma City | OK | $0 |
| Hartcorn Plumbing & Heating, Inc. | Ronkonkoma | NY | $0 |
| Hart Engineering Corp. | Cumberland | RI | Subcontractor |
| Harvey Services Inc. | Morton | MS | $0 |
| Hase Plumbing, Heating & Air Conditioning, Inc. | Aberdeen | SD | $0 |
| Haustechnik Bachmaier GMBH | Garmisch-partenkirchen | | $0 |
| Hawaiian Air Conditioning And Refrigeration, LLC | Kapolei | HI | $0 |
| Hawaii Fireplaces, Inc. | Kamuela | HI | Subcontractor |
| Hawk Mechanical Contractors, Inc. | Monroe | WA | Subcontractor |
| Hawleys, Inc. | Benson | MN | $0 |
| Hay Mechanical Solutions Corp. | Jamaica | NY | $0 |
| Hays Plumbing & Heating Inc. | Las Vegas | NM | $0 |
| Hays Service, LLC De | Macon | GA | $0 |
| HBC Mechanical LLC | Frisco | CO | Subcontractor |
| H.b. Mcclure Company, LLC | Harrisburg | PA | $0 |
| H & B Mechanical, Inc. | Hesperia | CA | Subcontractor |
| H, D, L & M Construction Services, Inc. | Albuquerque | NM | Subcontractor |
| H & D Mechanical LLC | Upper Marlboro | MD | Subcontractor |
| Heat-me, Inc. | Fairbanks | AK | $0 |
| Heeter Plumbing LLC | Dayton | OH | Subcontractor |
| Heide & Cook LLC | Honolulu | HI | Subcontractor |
| Hema Corporation | Tamuning | GU | Subcontractor |
| Hengel Brothers Inc. | La Crosse | WI | $0 |
| Henry Steckman Plumbing | Abilene | KS | $0 |
| Heritage Mechanical Inc. | Suquamish | WA | Subcontractor |
| Heritage Mechanical Services, Inc. | Farmingdale | NY | Subcontractor |
| Herman Plumbing Co. Inc. | Grand Island | NE | $0 |
| HHN & Associates LLC | Birmingham | AL | $0 |
| Hicks & Ingle Corporation | Knoxville | TN | Subcontractor |
| High Desert Refrigeration & Heating | Barstow | CA | Subcontractor |
| Highland Park Mechanical Inc. | Zion | IL | Subcontractor |
| Hilliard's Heating And Plumbing, Inc. | Pullman | WA | $0 |
| Hill Mechanical Corp. | Franklin Park | IL | Subcontractor |
| Hill Mechanical Of Georgia, LLC | Marietta | GA | $0 |
| Hills Plumbing & Heating, Inc. | Bemidji | MN | $0 |
| Hinton Refrigeration Co. | Oklahoma City | OK | $0 |
| Hi-tech Air Conditioning Service, Inc. | West Babylon | NY | $0 |
| Hj Norris, LLC | Moss Point | MS | $0 |
| HKS Energy Solutions Inc. | Tulsa | OK | $0 |
| H. L. Moe Co. Inc. | Glendale | CA | Subcontractor |
| Hm 2 Corporation | Titusville | FL | Subcontractor |
| Hobson Fabricating Corp. | Boise | ID | $0 |
| Holbrook Servco, LP | Salt Lake City | UT | Subcontractor |
| Holmberg Company | Bellevue | WA | Subcontractor |
| Holtville Air Conditioning & Electrical, Inc. | Holtville | CA | $0 |
| Honeywell International Inc. | Honolulu | HI | Subcontractor |
| Honolulu Fire Protection LLC | Waipahu | HI | Subcontractor |
| Hood HTG Air PLG Electric, Inc. | Concordia | KS | $0 |
| Horton Mechanical Contractors Inc. | Baltimore | MD | $0 |
| Hospitality Services LLC | Johns Island | SC | $0 |
| Hot And Cold Corporation | Clinton | MD | $0 |
| Hot Rod Mechanical, Inc. | Austin | TX | $0 |
| Houseman Refrigeration, LLC | Albion | NY | Subcontractor |
| Howe Boiler Company Inc. | Huntington Beach | CA | Subcontractor |
| Hsi Mechanical Inc. | Honolulu | HI | Subcontractor |
| HTF Mechanical Services Inc. | Moneta | VA | $0 |
| Hti Ltd. | Houston | TX | Subcontractor |
| Hudson P. Davis, Inc. | Vista | CA | Subcontractor |
| Hukill's Inc. | Fort Worth | TX | $0 |
| Humphrey Mechanical Inc. | Jacksonville | NC | Subcontractor |
| Huneke Associates Inc. | Merchantville | NJ | $0 |
| Hutson & Sons Boiler & Welding Inc. | Indianapolis | IN | $0 |
| H V A C, Inc. | Bristol | TN | $0 |
| Hyatt Refrigeration, Inc. | Yuma | AZ | $0 |
| Hyde-stone Mechanical Contractors, Inc. | Watertown | NY | Subcontractor |
| Hydrametrics, LLC | Hugo | MN | Subcontractor |
| Hydro-temp Mechanical, Inc. | Wilsonville | OR | $0 |
| Hyvac Inc. | Coconut Creek | FL | $0 |
| Ice Cold, LLC | North Charleston | SC | Subcontractor |
| Icom Mechanical, Inc. | San Jose | CA | Subcontractor |
| Icon Boiler Inc. | Greensboro | NC | Subcontractor |
| Icon Mechanical Construction & Engineering LLC | Granite City | IL | Subcontractor |
| I L Mechanical, Inc. | Hayward | CA | Subcontractor |
| Independent Air Systems, Inc. | White Plains | MD | Subcontractor |
| Independent Mechanical Contractors, Inc. | Woburn | MA | Subcontractor |
| Industrial Burner Service, Inc. | Providence | RI | $0 |
| Industrial Commercial Systems, Inc. | Vista | CA | Subcontractor |
| Industrial Fire Sprinkler Co. Inc. | San Diego | CA | Subcontractor |
| Industrial Sprinkler Corp. | Arecibo | PR | Subcontractor |
| Infinity Air Inc. | Carolina | PR | Subcontractor |
| Innovative Mechanical Systems Inc. | Mechanicsville | MD | $0 |
| Intech Mechanical Company LLC | Roseville | CA | Subcontractor |
| Integrated Facility Services Inc. | Fenton | MO | Subcontractor |
| Intermech Inc. | Richland | WA | Subcontractor |
| Intermountain Heating & Air Conditioning Inc. | Helena | MT | $0 |
| International Mechanical Services, Inc. | San Antonio | TX | Subcontractor |
| Interstate Service Co. Inc. | Brentwood | MD | $0 |
| Inter Tech Mechanical Services Inc. | Louisville | KY | Subcontractor |
| Ipc Lydon, LLC | Avon | MA | Subcontractor |
| Iron Mountain Fire Protection - TX, Inc. | Alvarado | TX | Subcontractor |
| Irontree Construction, Inc. | Mesa | AZ | $0 |
| Ishc, Inc. | Albuquerque | NM | Subcontractor |
| Island Controls, Inc. | Honolulu | HI | Subcontractor |
| Ivey Air, Inc. | Levittown | PA | $0 |
| Ivey Mechanical Company, LLC | Kosciusko | MS | Subcontractor |
| Jabo Incorporated | Ypsilanti | MI | $0 |
