Wyoming climate zones and HVAC design temperatures
Wyoming spans 3 IECC climate zones. 70% of people live in zone 6B (cold, dry). In Cheyenne, heating and cooling equipment is sized for 88°F in summer and 3°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Cheyenne | 5B | 88°F | 3°F | 50°F |
| Casper | 6B | 92°F | -2°F | 48°F |
| Laramie | 6B | 84°F | -2°F | 45°F |
| Gillette | 6B | 92°F | -4°F | 49°F |
| Rock Springs | 6B | 87°F | 1°F | 46°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: 95°F (Big Horn County); coldest winter design: -11°F (Sublette County).
Typical equipment sizes in Cheyenne
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Cheyenne'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 + 8 kW backup |
| 2,000 sq ft | 2.5 tons | 60,000 BTU | 2.5 tons + 10 kW backup |
| 2,500 sq ft | 3 tons | 60,000 BTU | 3 tons + 10 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 5B: cool, dry (3 counties, 21% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Goshen County | 94°F | 0°F |
| Laramie County | 88°F | 3°F |
| Platte County | 94°F | 0°F |
Zone 6B: cold, dry (17 counties, 70% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Albany County | 84°F | -2°F |
| Big Horn County | 95°F | -7°F |
| Campbell County | 92°F | -4°F |
| Carbon County | 88°F | 1°F |
| Converse County | 93°F | -3°F |
| Crook County | 90°F | -4°F |
| Fremont County | 90°F | -4°F |
| Hot Springs County | 93°F | -7°F |
| Johnson County | 90°F | -2°F |
| Natrona County | 92°F | -2°F |
| Niobrara County | 93°F | -3°F |
| Park County | 88°F | -5°F |
| Sheridan County | 93°F | -4°F |
| Sweetwater County | 87°F | 1°F |
| Uinta County | 86°F | 4°F |
| Washakie County | 93°F | -7°F |
| Weston County | 85°F | -2°F |
Zone 7: very cold (3 counties, 9% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Lincoln County | 82°F | -8°F |
| Sublette County | 82°F | -11°F |
| Teton County | 83°F | -9°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.