Utah climate zones and HVAC design temperatures
Utah spans 3 IECC climate zones. 90% of people live in zone 5B (cool, dry). In Salt Lake City, heating and cooling equipment is sized for 98°F in summer and 20°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Salt Lake City | 5B | 98°F | 20°F | 58°F |
| Provo | 5B | 94°F | 17°F | 54°F |
| Ogden | 5B | 96°F | 16°F | 56°F |
| St. George | 3B | 104°F | 28°F | 66°F |
| Logan | 5B | 93°F | 5°F | 50°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: 104°F (Washington County); coldest winter design: -1°F (Garfield County).
Typical equipment sizes in Salt Lake City
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Salt Lake City'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 tons | 40,000 BTU | 2 tons + 5 kW backup |
| 2,000 sq ft | 3 tons | 40,000 BTU | 3 tons + 5 kW backup |
| 2,500 sq ft | 3.5 tons | 40,000 BTU | 3.5 tons + 5 kW backup |
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 3B: warm, dry (1 county, 6% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Washington County | 104°F | 28°F |
Zone 5B: cool, dry (21 counties, 90% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Beaver County | 97°F | 8°F |
| Box Elder County | 95°F | 13°F |
| Cache County | 93°F | 5°F |
| Carbon County | 93°F | 11°F |
| Davis County | 93°F | 15°F |
| Emery County | 93°F | 11°F |
| Garfield County | 84°F | -1°F |
| Grand County | 99°F | 13°F |
| Iron County | 93°F | 11°F |
| Juab County | 94°F | 17°F |
| Kane County | 100°F | 16°F |
| Millard County | 97°F | 10°F |
| Piute County | 84°F | -1°F |
| Salt Lake County | 98°F | 20°F |
| San Juan County | 92°F | 16°F |
| Sanpete County | 93°F | 11°F |
| Sevier County | 97°F | 10°F |
| Tooele County | 98°F | 20°F |
| Utah County | 94°F | 17°F |
| Wayne County | 84°F | -1°F |
| Weber County | 96°F | 16°F |
Zone 6B: cold, dry (7 counties, 5% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Daggett County | 93°F | 2°F |
| Duchesne County | 93°F | 2°F |
| Morgan County | 93°F | 15°F |
| Rich County | 93°F | 5°F |
| Summit County | 98°F | 20°F |
| Uintah County | 93°F | 2°F |
| Wasatch County | 94°F | 17°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.