Alaska climate zones and HVAC design temperatures
Alaska spans 4 IECC climate zones. 68% of people live in zone 7 (very cold). In Anchorage, heating and cooling equipment is sized for 72°F in summer and -4°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Anchorage | 7 | 72°F | -4°F | 41°F |
| Fairbanks | 8 | 79°F | -35°F | 35°F |
| Juneau | 6A | 72°F | 12°F | 45°F |
| Wasilla | 7 | 73°F | -11°F | 40°F |
| Sitka | 5C | 65°F | 24°F | 49°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 borough or census area from NOAA hourly weather data, 2015-2024; see where our numbers come from. Hottest summer design in the state: 79°F (Fairbanks North Star Borough); coldest winter design: -38°F (Yukon-Koyukuk Census Area).
Typical equipment sizes in Anchorage
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Anchorage'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 | 1.5 tons | 40,000 BTU | 1.5 tons + 10 kW backup |
| 2,000 sq ft | 2 tons | 60,000 BTU | 2 tons + 15 kW backup |
| 2,500 sq ft | 2.5 tons | 60,000 BTU | 2.5 tons + 15 kW backup |
AC size calculator Furnace size calculator Heat pump size calculator
Climate zone by borough or census area
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 5C: cool, marine (3 boroughs and census areas, 4% of people)
| Borough or census area | Summer 1% | Winter 99% |
|---|---|---|
| Ketchikan Gateway Borough | 71°F | 21°F |
| Prince of Wales-Hyder Census Area | 68°F | 20°F |
| Sitka City and Borough | 65°F | 24°F |
Zone 6A: cold, humid (7 boroughs and census areas, 8% of people)
| Borough or census area | Summer 1% | Winter 99% |
|---|---|---|
| Haines Borough | 71°F | 6°F |
| Hoonah-Angoon Census Area | 67°F | 7°F |
| Juneau City and Borough | 72°F | 12°F |
| Kodiak Island Borough | 68°F | 16°F |
| Petersburg Borough | 67°F | 13°F |
| Skagway Municipality | 69°F | 9°F |
| Wrangell City and Borough | 70°F | 18°F |
Zone 7: very cold (12 boroughs and census areas, 68% of people)
| Borough or census area | Summer 1% | Winter 99% |
|---|---|---|
| Aleutians East Borough | 59°F | 17°F |
| Aleutians West Census Area | 61°F | 25°F |
| Anchorage Municipality | 72°F | -4°F |
| Bethel Census Area | 70°F | -16°F |
| Bristol Bay Borough | 70°F | -11°F |
| Chugach Census Area | 68°F | 7°F |
| Copper River Census Area | 75°F | -30°F |
| Dillingham Census Area | 68°F | -9°F |
| Kenai Peninsula Borough | 70°F | -12°F |
| Lake and Peninsula Borough | 70°F | -11°F |
| Matanuska-Susitna Borough | 73°F | -11°F |
| Yakutat City and Borough | 66°F | 11°F |
Zone 8: subarctic (8 boroughs and census areas, 20% of people)
| Borough or census area | Summer 1% | Winter 99% |
|---|---|---|
| Denali Borough | 72°F | -33°F |
| Fairbanks North Star Borough | 79°F | -35°F |
| Kusilvak Census Area | 68°F | -13°F |
| Nome Census Area | 64°F | -19°F |
| North Slope Borough | 55°F | -30°F |
| Northwest Arctic Borough | 71°F | -34°F |
| Southeast Fairbanks Census Area | 76°F | -26°F |
| Yukon-Koyukuk Census Area | 76°F | -38°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.