DOE climate zones by state
HVAC sizing is organised around the DOE climate zones, numbered 1 for the hottest to 8 for the coldest. They come from the IECC map, which assigns a zone to every US county using heating and cooling degree days and a moisture regime.
Large states span several zones. Texas covers zones 1 through 3, Michigan 5 through 7, California 3 through 4. The table gives the dominant zone and the full range, and if your state shows a range you should check which end your county sits at before trusting a single number.
What each zone means
| Zone | Character | Cooling BTU/sq ft | Heating BTU/sq ft | Example cities |
|---|---|---|---|---|
| 1 | hot humid | 30 to 35 | 15 to 25 | Miami, Key West, Honolulu |
| 2 | hot | 27 to 30 | 20 to 30 | Houston, Orlando, Phoenix, New Orleans |
| 3 | warm | 24 to 27 | 25 to 35 | Atlanta, Dallas, Los Angeles, Charlotte |
| 4 | mixed | 22 to 25 | 30 to 40 | Washington DC, Seattle, St Louis, Nashville |
| 5 | cool | 20 to 23 | 35 to 45 | Chicago, Denver, Boston, Detroit |
| 6 | cold | 18 to 22 | 40 to 50 | Minneapolis, Burlington, Helena |
| 7 | very cold | 16 to 20 | 45 to 55 | Duluth, Grand Forks, International Falls |
| 8 | subarctic | 15 to 18 | 50 to 60 | Fairbanks, Barrow |
Every state
| State | Dominant zone | Range | Cooling load, 1,500 sq ft | Heating load, 1,500 sq ft |
|---|---|---|---|---|
| Alabama | 2 | 2 to 3 | 42,188 | 35,625 |
| Alaska | 7 | 7 to 8 | 26,250 | 73,125 |
| Arizona | 2 | 2 to 5 | 42,188 | 35,625 |
| Arkansas | 3 | 3 to 4 | 37,688 | 43,125 |
| California | 3 | 3 to 4 | 37,688 | 43,125 |
| Colorado | 5 | 5 to 7 | 31,688 | 58,125 |
| Connecticut | 5 | 5 | 31,688 | 58,125 |
| Delaware | 4 | 4 | 34,688 | 50,625 |
| District of Columbia | 4 | 4 | 34,688 | 50,625 |
| Florida | 1 | 1 to 2 | 47,813 | 28,125 |
| Georgia | 2 | 2 to 4 | 42,188 | 35,625 |
| Hawaii | 1 | 1 | 47,813 | 28,125 |
| Idaho | 5 | 5 to 6 | 31,688 | 58,125 |
| Illinois | 4 | 4 to 5 | 34,688 | 50,625 |
| Indiana | 4 | 4 to 5 | 34,688 | 50,625 |
| Iowa | 5 | 5 to 6 | 31,688 | 58,125 |
| Kansas | 4 | 4 to 5 | 34,688 | 50,625 |
| Kentucky | 4 | 4 | 34,688 | 50,625 |
| Louisiana | 2 | 2 to 3 | 42,188 | 35,625 |
| Maine | 6 | 6 to 7 | 29,250 | 65,625 |
| Maryland | 4 | 4 to 5 | 34,688 | 50,625 |
| Massachusetts | 5 | 5 | 31,688 | 58,125 |
| Michigan | 5 | 5 to 7 | 31,688 | 58,125 |
| Minnesota | 6 | 6 to 7 | 29,250 | 65,625 |
| Mississippi | 2 | 2 to 3 | 42,188 | 35,625 |
| Missouri | 4 | 4 to 5 | 34,688 | 50,625 |
| Montana | 6 | 6 to 7 | 29,250 | 65,625 |
| Nebraska | 5 | 5 | 31,688 | 58,125 |
| Nevada | 3 | 3 to 5 | 37,688 | 43,125 |
| New Hampshire | 5 | 5 to 6 | 31,688 | 58,125 |
| New Jersey | 4 | 4 to 5 | 34,688 | 50,625 |
| New Mexico | 3 | 3 to 5 | 37,688 | 43,125 |
| New York | 4 | 4 to 6 | 34,688 | 50,625 |
| North Carolina | 3 | 3 to 5 | 37,688 | 43,125 |
| North Dakota | 6 | 6 to 7 | 29,250 | 65,625 |
| Ohio | 4 | 4 to 5 | 34,688 | 50,625 |
| Oklahoma | 3 | 3 to 4 | 37,688 | 43,125 |
| Oregon | 4 | 4 to 5 | 34,688 | 50,625 |
| Pennsylvania | 4 | 4 to 6 | 34,688 | 50,625 |
| Rhode Island | 5 | 5 | 31,688 | 58,125 |
| South Carolina | 2 | 2 to 3 | 42,188 | 35,625 |
| South Dakota | 5 | 5 to 6 | 31,688 | 58,125 |
| Tennessee | 3 | 3 to 4 | 37,688 | 43,125 |
| Texas | 1 | 1 to 3 | 47,813 | 28,125 |
| Utah | 5 | 5 to 6 | 31,688 | 58,125 |
| Vermont | 6 | 6 | 29,250 | 65,625 |
| Virginia | 4 | 4 | 34,688 | 50,625 |
| Washington | 4 | 4 to 6 | 34,688 | 50,625 |
| West Virginia | 4 | 4 to 5 | 34,688 | 50,625 |
| Wisconsin | 6 | 6 to 7 | 29,250 | 65,625 |
| Wyoming | 5 | 5 to 7 | 31,688 | 58,125 |
Load figures use the dominant zone at 8 ft ceilings with average insulation. In a state spanning several zones, a house at the cold end can need noticeably more heat than this table suggests.
Frequently asked questions
What climate zone am I in?
DOE climate zones are assigned by county, not by state, and the table on this page gives the dominant zone for each state plus the range it spans. If your state spans several zones, check which end your county sits at, because the difference between adjacent zones is roughly 10 to 15 percent of load.
How many climate zones are there in the US?
Eight, numbered 1 for the hottest (south Florida, Hawaii) to 8 for the coldest (interior Alaska). Zones are further divided by moisture regime into moist, dry and marine, which affects construction requirements more than equipment sizing.
Why does climate zone change what size air conditioner I need?
Because the design temperature difference between inside and outside is what the equipment has to overcome. In zone 1 the cooling load is roughly twice the zone 8 figure per square foot, and the heating load runs the opposite way, which is why a single national BTU-per-square-foot number cannot be right everywhere.