Zone 1 — Hot (≈28 BTU/sq ft): Florida, the Gulf Coast, south Texas, Phoenix/Tucson, southern Nevada. Zone 2 — Warm (≈25): the rest of the Deep South, most of Texas, southern California inland. Zone 3 — Moderate (≈22): Tennessee, the Carolinas, Missouri, Kansas, coastal California. Zone 4 — Mild (≈20): the Mid-Atlantic, Ohio Valley, Pacific Northwest. Zone 5 — Cool (≈18): Minnesota, Wisconsin, upstate New York, New England, the Mountain West's high country.
Simplified placements for AC sizing — large states span zones, so the notes name the split. When in doubt, size for the hotter zone if your summers regularly exceed 95°F.
| State | Zone | State | Zone |
|---|---|---|---|
| Alabama | 2 | Montana | 5 |
| Alaska | 5 | Nebraska | 3–4 |
| Arizona | 1–3 (Phoenix 1, Flagstaff 3) | Nevada | 1–4 (Vegas 1, Reno 4) |
| Arkansas | 2 | New Hampshire | 5 |
| California | 2–4 (inland S. 2, coast 3, N. 4) | New Jersey | 3–4 |
| Colorado | 4–5 | New Mexico | 2–4 |
| Connecticut | 4 | New York | 4–5 |
| Delaware | 3–4 | North Carolina | 3 |
| Florida | 1 | North Dakota | 5 |
| Georgia | 2 | Ohio | 4 |
| Hawaii | 1 | Oklahoma | 2–3 |
| Idaho | 4–5 | Oregon | 4 |
| Illinois | 3–4 | Pennsylvania | 4 |
| Indiana | 3–4 | Rhode Island | 4 |
| Iowa | 4 | South Carolina | 2 |
| Kansas | 3 | South Dakota | 4–5 |
| Kentucky | 3 | Tennessee | 3 |
| Louisiana | 1–2 | Texas | 1–2 (Gulf/S. 1, rest 2) |
| Maine | 5 | Utah | 3–4 |
| Maryland & DC | 3–4 | Vermont | 5 |
| Massachusetts | 4–5 | Virginia | 3 |
| Michigan | 4–5 | Washington | 4 |
| Minnesota | 5 | West Virginia | 4 |
| Mississippi | 2 | Wisconsin | 5 |
| Missouri | 3 | Wyoming | 5 |
Two cities at the same temperature differ in latent load: Houston's humidity makes its effective load heavier than Phoenix's at identical thermometer readings, and it punishes oversizing harder. In humid zones, never size up 'for safety' — see why oversizing backfires.
The tonnage calculator bakes these zone rates in and layers the building factors on top. Border areas: pick the hotter zone if your summers regularly exceed 95°F.
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South Texas and the Gulf Coast size as Zone 1 (~28 BTU/sq ft); the rest of the state mostly Zone 2 (~25).
They're aligned in spirit but inverted in numbering and simplified for cooling-load purposes — IECC zones count upward from hot (1) to subarctic (8) for building-code insulation, while sizing tables compress this to five cooling tiers.
Put the numbers to work: AC tonnage calculator · bill calculator · model number decoder.