| Alabama | Alabama Board of Heating, Air Conditioning and Refrigeration Contractors ↗ | Guide |
| Alaska | Alaska Department of Labor, Mechanical Inspection ↗ | Guide |
| Arizona | Arizona Registrar of Contractors ↗ | Guide |
| Arkansas | Arkansas Department of Labor and Licensing (HVACR) ↗ | Guide |
| California | Contractors State License Board (C-20) ↗ | Guide |
| Colorado | No statewide license in Colorado for this work. Your city or county licenses it. | Guide |
| Connecticut | Connecticut Department of Consumer Protection ↗ | Guide |
| Delaware | Delaware Board of Plumbing, Heating, Ventilation, Air Conditioning and Refrigeration Examiners ↗ | Guide |
| District of Columbia | DC Department of Licensing and Consumer Protection ↗ | Guide |
| Florida | Florida Construction Industry Licensing Board (DBPR) ↗ | Guide |
| Georgia | Georgia State Construction Industry Licensing Board (conditioned air) ↗ | Guide |
| Hawaii | Hawaii Contractors License Board ↗ | Guide |
| Idaho | Idaho Division of Occupational and Professional Licenses ↗ | Guide |
| Illinois | No statewide license in Illinois for this work. Your city or county licenses it. | Guide |
| Indiana | No statewide license in Indiana for this work. Your city or county licenses it. | Guide |
| Iowa | Iowa Plumbing and Mechanical Systems Board ↗ | Guide |
| Kansas | No statewide license in Kansas for this work. Your city or county licenses it. | Guide |
| Kentucky | Kentucky Department of Housing, Buildings and Construction ↗ | Guide |
| Louisiana | Louisiana State Licensing Board for Contractors ↗ | Guide |
| Maine | Maine Fuel Board ↗ | Guide |
| Maryland | Maryland HVACR Board ↗ | Guide |
| Massachusetts | Massachusetts Office of Public Safety and Inspections (refrigeration) ↗ | Guide |
| Michigan | Michigan LARA Bureau of Construction Codes (mechanical) ↗ | Guide |
| Minnesota | No statewide license in Minnesota for this work. Your city or county licenses it. | Guide |
| Mississippi | Mississippi State Board of Contractors ↗ | Guide |
| Missouri | No statewide license in Missouri for this work. Your city or county licenses it. | Guide |
| Montana | No statewide license in Montana for this work. Your city or county licenses it. | Guide |
| Nebraska | No statewide license in Nebraska for this work. Your city or county licenses it. | Guide |
| Nevada | Nevada State Contractors Board ↗ | Guide |
| New Hampshire | New Hampshire Mechanical Licensing Board (OPLC) ↗ | Guide |
| New Jersey | New Jersey State Board of Examiners of HVACR Contractors ↗ | Guide |
| New Mexico | New Mexico Construction Industries Division ↗ | Guide |
| New York | No statewide license in New York for this work. Your city or county licenses it. | Guide |
| North Carolina | North Carolina State Board of Examiners of Plumbing, Heating and Fire Sprinkler Contractors ↗ | Guide |
| North Dakota | No statewide license in North Dakota for this work. Your city or county licenses it. | Guide |
| Ohio | Ohio Construction Industry Licensing Board ↗ | Guide |
| Oklahoma | Oklahoma Construction Industries Board ↗ | Guide |
| Oregon | Oregon Construction Contractors Board ↗ | Guide |
| Pennsylvania | No statewide license in Pennsylvania for this work. Your city or county licenses it. | Guide |
| Rhode Island | Rhode Island Department of Labor and Training ↗ | Guide |
| South Carolina | South Carolina LLR ↗ | Guide |
| South Dakota | No statewide license in South Dakota for this work. Your city or county licenses it. | Guide |
| Tennessee | Tennessee Board for Licensing Contractors ↗ | Guide |
| Texas | Texas Department of Licensing and Regulation (A/C and refrigeration) ↗ | Guide |
| Utah | Utah Division of Professional Licensing ↗ | Guide |
| Vermont | No statewide license in Vermont for this work. Your city or county licenses it. | Guide |
| Virginia | Virginia Board for Contractors (DPOR) ↗ | Guide |
| Washington | Washington Department of Labor and Industries ↗ | Guide |
| West Virginia | West Virginia State Fire Marshal ↗ | Guide |
| Wisconsin | Wisconsin Department of Safety and Professional Services ↗ | Guide |
| Wyoming | No statewide license in Wyoming for this work. Your city or county licenses it. | Guide |