| Jackson's Heating & Air Conditioning Company | Lagrange | GA | Subcontractor |
| Jake Marshall, LLC | Chattanooga | TN | Subcontractor |
| J & A Mechanical Contractors, Inc. | Oswego | NY | $0 |
| James L. Cayton Associates, Inc. | New Bern | NC | Subcontractor |
| James Long Construction Services, Inc. | Sacramento | CA | Subcontractor |
| James River Mechanical Inc. | Smithfield | VA | Subcontractor |
| Jayhawk Fire Sprinkler Co. Inc. | Olathe | KS | Subcontractor |
| Jayvee Air Conditioning & General Contractor LLC | Bayamon | PR | $0 |
| Jb Hvac Inc. | Mays Landing | NJ | $0 |
| J B S Plumbing Services Incorporated | Spring | TX | $0 |
| J. Butrick, Inc. | Granite Bay | CA | Subcontractor |
| JCM Associates, Inc. | Upper Marlboro | MD | Subcontractor |
| J.C.M. Control Systems, Inc. | Lutherville Timonium | MD | Subcontractor |
| JD'S Plumbing, Inc. | Seaside | CA | $0 |
| JDS Plumbing & Mechanical | Vista | CA | Subcontractor |
| Jeffcoat & Associates, LLC | Bessemer | AL | $0 |
| Jefferson Sprinkler, Incorporated | Gretna | LA | Subcontractor |
| Jem LLC | Waveland | MS | Subcontractor |
| J. F. Fischer, Inc. | Baltimore | MD | Subcontractor |
| J-goods Plumbing & Heating LLC | Negaunee | MI | $0 |
| J.g. Tate Fire Protection Systems, Inc. | Poway | CA | Subcontractor |
| Jh Kelly, LLC | Longview | WA | Subcontractor |
| Jim Brown Construction Co. | Mountain Home | AR | $0 |
| J.l. Brady Co. LLC | Moline | IL | Subcontractor |
| Jmac Plumbing & Air Conditioning LLC | Las Vegas | NV | $0 |
| J M Brennan Inc. | Milwaukee | WI | $0 |
| J.m. Oliver, Inc. | Morton | PA | Subcontractor |
| JMS Mechanical Inc. | Rohnert Park | CA | Subcontractor |
| J. Noble Binns Plumbing Company, Inc. | Bakersfield | CA | Subcontractor |
| Joel Grant | Lompoc | CA | $0 |
| Johansen Mechanical, Inc. | Monroe | WA | Subcontractor |
| John Crownover Service Company, Inc. | Ty Ty | GA | $0 |
| John C Schaub, Inc. | Mount Laurel | NJ | $0 |
| John P. Bell & Sons, LLC | Rochester | NY | $0 |
| John S. Bascom, Inc. | Moorpark | CA | Subcontractor |
| Johnson Boiler Works, Inc. | Benwood | WV | $0 |
| Johnson & Jordan Inc. | Scarborough | ME | Subcontractor |
| Johnsons Sewer And Drain Contractors, Inc. | Denton | MD | $0 |
| Jones Environmental Control Inc. | Mokena | IL | $0 |
| J.r. Barto Heating/air-conditioning/sheet Metal, Inc. | Orcutt | CA | Subcontractor |
| Julian Speer Co. | Columbus | OH | $0 |
| Justice, Inc. | Corpus Christi | TX | $0 |
| Jywco, Inc. | Norfolk | VA | Subcontractor |
| Kaa Investments LLC | Yakima | WA | Subcontractor |
| Kahoe Air Balance Co. | Eastlake | OH | $0 |
| Kansas City Mechanical Inc. | Edwardsville | KS | $0 |
| Kastens Plumbing & Heating, Inc. | Atchison | KS | $0 |
| K. C. Charles, Inc. | Nine Mile Falls | WA | Subcontractor |
| K Co. Inc. | Coventry Township | OH | $0 |
| Keith & Jacqueline Conroy Inc. | Pennsauken | NJ | Subcontractor |
| Kemp & Hilton Inc. | Salt Lake City | UT | $0 |
| Ken L Electric, Inc. | Saint Agatha | ME | Subcontractor |
| Ken's Refrigeration & Heating, Inc. | Wall | SD | $0 |
| Kent Island Mechanical, LLC | Burtonsville | MD | Subcontractor |
| Kent Mechanical, Inc. | Forsyth | GA | Subcontractor |
| Keystone Critical Systems & Advisors, LLC | West Palm Beach | FL | $0 |
| Kg Sheet Metal Services LLC | Upper Marlboro | MD | Subcontractor |
| King Industries Inc. | Chattanooga | TN | Subcontractor |
| Kingsaire, Inc. | El Paso | TX | $0 |
| King Soft Water Company | Spokane | WA | $0 |
| Kirk Williams Co. Inc. | Grove City | OH | $0 |
| Kissco Control Systems Inc. | San Mateo | CA | Subcontractor |
| Kj Plumbing & Heating, LLC | Delta | UT | $0 |
| Klebs Mechanical, Inc. | Anchorage | AK | Subcontractor |
| Kline Mechanical Contracting Inc. | Woodward | OK | $0 |
| Knight Mechanical Inc. | Hamel | MN | $0 |
| Koch Mechanical Inc. | North Vernon | IN | $0 |
| Korea O.c.u Industry | Seoul | | Subcontractor |
| Korrect Plumbing, Heating & Air Conditioning, Inc. | Dayton | OH | Subcontractor |
| Krier & Blain, Inc. | Sioux Falls | SD | $0 |
| Kruse Corp. | Wichita | KS | Subcontractor |
| K-T Heating & Air Conditioning Inc. | Hastings | NE | $0 |
| Kuchar Mechanical Inc. | Fort Pierce | FL | $0 |
| Kula Energy LLC | Rowley | MA | Subcontractor |
| Laboratory And Biosafety Systems, Inc. | Lawrenceville | GA | Subcontractor |
| Lagarde, Ltd. | Jefferson | LA | $0 |
| Landover Cooling Tower Service, LLC | Mountainside | NJ | $0 |
| Lane Plumbing Company, Inc. | Alamogordo | NM | $0 |
| Larratt Bros. Plumbing, Inc. | San Francisco | CA | $0 |
| Larry Stockwell's Heating And Air Conditioning, Inc. | Alexandria | LA | $0 |
| Larry Tronu Mechanical, Incorporated | Pensacola | FL | $0 |
| Larson Plumbing & Utility Co. | Odem | TX | $0 |
| Lawson Mechanical Contractors | Sacramento | CA | Subcontractor |
| Lawyer Mechanical Services Inc. | Las Vegas | NV | Subcontractor |
| Le Bel, Inc. | Abington | MA | $0 |
| Leblanc & Associates, L.L.C | Houma | LA | Subcontractor |
| Leblanc & Associates Refrigeration, Inc. | Houma | LA | $0 |
| Legacy Fire Protection LLC | Idaho Falls | ID | Subcontractor |
| Legacy Mechanical & Energy Services, Inc. | San Ramon | CA | $0 |
| Legacy Mechanical Services, LLC | Kennesaw | GA | Subcontractor |
| Leroy Bowlin Heating And Air Conditioning, Inc. | Greenville | MS | $0 |
| Lesters Fuel Oil Service, Inc. | Jacksonville | FL | $0 |
| Letsos Company | Houston | TX | $0 |
| L&H Airco, LLC | Rocklin | CA | Subcontractor |
| Liberty Mechanical Contractors | Newark | NJ | $0 |
| Lincoln Energy Mechanical Services, Inc. | West Warwick | RI | $0 |
| Little Big Plumbing LLC | Wahiawa | HI | $0 |
| Littles Plumbing LLC | Wheelersburg | OH | $0 |
| Littmann Industries, Inc. | Elmhurst | IL | $0 |
| L & L Boiler Maintenance Inc. | Montoursville | PA | $0 |
