Arizona climate zones and HVAC design temperatures
Arizona spans 4 IECC climate zones. 85% of people live in zone 2B (hot, dry). In Phoenix, heating and cooling equipment is sized for 110°F in summer and 43°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Phoenix | 2B | 110°F | 43°F | 79°F |
| Tucson | 2B | 104°F | 35°F | 72°F |
| Mesa | 2B | 110°F | 43°F | 79°F |
| Flagstaff | 5B | 85°F | 12°F | 50°F |
| Yuma | 2B | 110°F | 44°F | 78°F |
Summer: exceeded in 1% of hours. Winter: colder in only 1% of hours. Water in: estimated groundwater temperature for tankless water heater sizing. Computed for each county from NOAA hourly weather data, 2015-2024; see where our numbers come from. Hottest summer design in the state: 112°F (La Paz County); coldest winter design: 8°F (Apache County).
Typical equipment sizes in Phoenix
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Phoenix's design temperatures. Your house can need more or less; use the calculators for yours.
| House | Central AC | Gas furnace (95% AFUE) | Heat pump |
|---|---|---|---|
| 1,500 sq ft | 2.5 tons | 40,000 BTU | 2.5 tons |
| 2,000 sq ft | 3 tons | 40,000 BTU | 3 tons |
| 2,500 sq ft | 4 tons | 40,000 BTU | 4 tons |
AC size calculator Furnace size calculator Heat pump size calculator
Climate zone by county
From the 2021 International Energy Conservation Code (IECC), as published by the U.S. Department of Energy. The zone sets the insulation and window requirements in the energy code; the number runs from 1 (hottest) to 8 (coldest), and the letter is A for moist, B for dry and C for marine.
Zone 2B: hot, dry (5 counties, 85% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| La Paz County | 112°F | 40°F |
| Maricopa County | 110°F | 43°F |
| Pima County | 104°F | 35°F |
| Pinal County | 110°F | 43°F |
| Yuma County | 110°F | 44°F |
Zone 3B: warm, dry (5 counties, 6% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Cochise County | 95°F | 31°F |
| Graham County | 104°F | 30°F |
| Greenlee County | 104°F | 30°F |
| Mohave County | 102°F | 28°F |
| Santa Cruz County | 99°F | 30°F |
Zone 4B: mixed, dry (2 counties, 4% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Gila County | 93°F | 27°F |
| Yavapai County | 93°F | 22°F |
Zone 5B: cool, dry (3 counties, 4% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Apache County | 90°F | 8°F |
| Coconino County | 85°F | 12°F |
| Navajo County | 98°F | 16°F |
Climate data as of 2026-10. Design temperatures may differ by a few degrees from the ACCA Manual J tables your contractor uses; winter values run a little warmer because recent winters have been milder.