| M J Services Inc. | San Diego | CA | $0 |
| MLN Service Company | Stafford | TX | $0 |
| M & M Facility Services LLC | Douglassville | PA | $0 |
| MMM Plumbing Heating & Air Conditioning Inc. | Amarillo | TX | Subcontractor |
| Mock Plumbing & Mechanical Inc. | Savannah | GA | Subcontractor |
| Modan Construction Services LLC | Fernandina Beach | FL | Subcontractor |
| Modern Piping, Inc. | Cedar Rapids | IA | Subcontractor |
| Mollenberg-betz, Inc. | Buffalo | NY | $0 |
| Monaco Mechanical Inc. | Lisle | IL | Subcontractor |
| Monroe Plumbing And Heating Co. | Monroe | MI | $0 |
| Morgan & Thornburg, Incorporated | Memphis | TN | $0 |
| Morrison Inc. | Marietta | OH | $0 |
| Moseley Hvac LLC | Paron | AR | $0 |
| Mpi Services LLC | Midvale | UT | Subcontractor |
| M. S. Johnston Co. Inc. | Hagerstown | MD | $0 |
| MSS Solutions, LLC | Charlotte | NC | Subcontractor |
| Mta Holdings Inc. | Farmington | NM | $0 |
| Mtech Mechanical Technologies Group, Inc. | Denver | CO | Subcontractor |
| Mundy's Heating & Air, Inc. | Murphy | NC | $0 |
| Murphy Company Mechanical Contractors And Engineers | Saint Louis | MO | Subcontractor |
| Murray Plumbing & Heating Corporation | Compton | CA | Subcontractor |
| Nagelbush Mechanical, Inc. | Fort Lauderdale | FL | Subcontractor |
| Nash Plumbing & Mechanical LLC | Belleview | FL | Subcontractor |
| Nashville Sheet Metal, LLC | Nashville | TN | $0 |
| National Hvac Service, Ltd. | Nashville | TN | $0 |
| Nationwide Refrigeration, Inc. | Manassas | VA | $0 |
| Naylor Heating & Refrigeration, LLC | Bemidji | MN | $0 |
| N.C.S. Corporation | Tacoma | WA | Subcontractor |
| Nebraska Fire Sprinkler Corp. | Alda | NE | $0 |
| Nederman Corporation | Charlotte | NC | $0 |
| Nelson & Company Engineered Service LLC | Jacksonville | FL | Subcontractor |
| Nemar Technology Group | San Juan | PR | $0 |
| Nesi Solutions LLC | Doral | FL | $0 |
| N. E. Tech-air, Inc. | Scarborough | ME | Subcontractor |
| Nevada Chiller & Boiler Inc. | Sparks | NV | $0 |
| New England Air Systems LLC | Williston | VT | $0 |
| New England Orbital Services, Inc. | Salem | NH | Subcontractor |
| New York Boiler, Inc. | Brooklyn | NY | $0 |
| New York Plumbing-heating-cooling Corp. | Richmond Hill | NY | $0 |
| Nexgen Mechanical, Inc. | Warwick | RI | Subcontractor |
| Nifco Mechanical Systems, LLC | Lincoln | NE | Subcontractor |
| N&J'S Plumbing & Hvac, LLC | Bosque Farms | NM | $0 |
| Norpac Sheet Metal, Inc. | Billings | MT | $0 |
| Norstar Heating & Cooling, Inc. | Colville | WA | Subcontractor |
| North Central Mechanical Inc. | Saint Marys | PA | Subcontractor |
| Northeast Coil Inc. | Arundel | ME | $0 |
| North East Fire Protection Systems, Inc. | Ballston Spa | NY | $0 |
| Northeast Mechanical Services, Inc. | Williamstown | NJ | $0 |
| Northern Heating & Plumbing, Inc. | Hancock | MI | $0 |
| North Idaho Heating & Cooling Solutions Inc. | Dalton Gardens | ID | $0 |
| Northland Refrigeration Inc. | Clearwater | MN | Subcontractor |
| North Mechanical Contracting Inc. | Indianapolis | IN | Subcontractor |
| North Pole Air Conditioning & Heating Inc. | Springfield Gardens | NY | $0 |
| Northwind Heating And Air Conditioning, Co. | Winchester | VA | $0 |
| Notch Welding & Mechanical Contractors Inc. | Chicopee | MA | Subcontractor |
| N. & T. Mechanical Contractors, Inc. | Sterling | MA | Subcontractor |
| Oahu Plumbing & Sheet Metal, Limited | Honolulu | HI | Subcontractor |
| Oasis Air Conditioning, Heating And Sheet Metal | Fallon | NV | Subcontractor |
| Oasis Hc LLC | Robinson | TX | $0 |
| Obr Cooling Towers LLC | Northwood | OH | Subcontractor |
| Ocean View Heating And Cooling, LLC | Norfolk | VA | $0 |
| O C Mcdonald Co. Inc. | San Jose | CA | $0 |
| Ocm Construction, Inc. | Tonawanda | NY | $0 |
| Ogborn Plumbing Contracting, Inc. | Tonasket | WA | Subcontractor |
| Ohio Heating & Air Conditioning Inc. | Columbus | OH | $0 |
| O. J. Laughlin Plumbing Company, Inc. | Valley Park | MO | Subcontractor |
| Oklahoma Fire Protection LLC | Oklahoma City | OK | Subcontractor |
| Olson Plumbing And Heating Company | Colorado Springs | CO | Subcontractor |
| Omega Test & Balance, L.L.C. | Phoenix | AZ | Subcontractor |
| Omni Pump Repairs, Inc. | Franklin Park | IL | $0 |
| One Call Inc. | Slidell | LA | $0 |
| Orrville Plumbing And Heating Inc. | Orrville | OH | $0 |
| Otter Creek Mechanical, Inc. | Waterbury | NE | $0 |
| Ozark Fire Sprinkler Co. Inc. | Warsaw | MO | Subcontractor |
| P1 Construction LLC | Lenexa | KS | Subcontractor |
| P1 Service LLC | Lenexa | KS | Subcontractor |
| Pacific Air Comfort, Inc. | Roseburg | OR | $0 |
| Pacific North LLC | Spanish Fork | UT | $0 |
| Pacific Rim Mechanical Contractors, Inc. | San Diego | CA | $0 |
| Pacific Test And Balance, LLC | Waipahu | HI | Subcontractor |
| Palm Beach Mechanical Inc. | Boynton Beach | FL | $0 |
| Palmer And Sicard, Inc. | Exeter | NH | Subcontractor |
| Pan-pacific Mechanical LLC | Fountain Valley | CA | Subcontractor |
| Paradigm Mechanical LLC | Colmar | PA | $0 |
| Parker Hannifin Corporation | Sylacauga | AL | $0 |
| Parker's Heating And Air Conditioning, Inc. | Americus | GA | $0 |
| Parkes Mechanical & Metals Inc. | Muscle Shoals | AL | Subcontractor |
| Patriot Air Solutions LLC | Lawton | OK | Subcontractor |
| Patriot Fire Protection Inc. | Spokane Valley | WA | Subcontractor |
| Patterson Plumbing & Heating Inc. | Pueblo | CO | $0 |
| Paul J. Construction Corp. | Temecula | CA | Subcontractor |
| P & B Mechanical, Inc. | Tucson | AZ | $0 |
| PDF Mechanical LLC | Carthage | IN | $0 |
| Pedraza, Inc. | Chicago | IL | $0 |
| Pelican Plumbing And Piping, Inc. | Lake Charles | LA | $0 |
| Pendleton Creek Farms Construction Inc. | Vidalia | GA | Subcontractor |
| Pendleton Heating & Air-conditioning, Inc. | Pendleton | OR | $0 |
| Penn State Mechanical Contractors, Inc. | Wilkes Barre | PA | $0 |
| Performance Fire Protection, LLC | Mooresville | NC | Subcontractor |
| Performance Mechanical, Inc. | Universal City | TX | Subcontractor |
