North Dakota climate zones and HVAC design temperatures
North Dakota spans 2 IECC climate zones. 72% of people live in zone 6A (cold, humid). In Fargo, heating and cooling equipment is sized for 88°F in summer and -13°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Fargo | 6A | 88°F | -13°F | 46°F |
| Bismarck | 6A | 91°F | -11°F | 47°F |
| Grand Forks | 7 | 87°F | -16°F | 44°F |
| Minot | 7 | 89°F | -13°F | 46°F |
| Williston | 6A | 90°F | -15°F | 45°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: 92°F (McIntosh County); coldest winter design: -18°F (Burke County).
Typical equipment sizes in Fargo
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Fargo'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 | 60,000 BTU | 2 tons + 15 kW backup |
| 2,000 sq ft | 2.5 tons | 60,000 BTU | 2.5 tons + 15 kW backup |
| 2,500 sq ft | 3 tons | 80,000 BTU | 3.5 tons + 15 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 6A: cold, humid (37 counties, 72% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adams County | 91°F | -10°F |
| Barnes County | 86°F | -13°F |
| Billings County | 90°F | -12°F |
| Bowman County | 91°F | -10°F |
| Burleigh County | 91°F | -11°F |
| Cass County | 88°F | -13°F |
| Dickey County | 86°F | -11°F |
| Dunn County | 90°F | -12°F |
| Eddy County | 86°F | -13°F |
| Emmons County | 91°F | -11°F |
| Foster County | 86°F | -13°F |
| Golden Valley County | 90°F | -13°F |
| Grant County | 88°F | -11°F |
| Griggs County | 86°F | -13°F |
| Hettinger County | 90°F | -12°F |
| Kidder County | 91°F | -11°F |
| LaMoure County | 87°F | -13°F |
| Logan County | 87°F | -13°F |
| McIntosh County | 92°F | -7°F |
| McKenzie County | 90°F | -15°F |
| McLean County | 87°F | -14°F |
| Mercer County | 90°F | -15°F |
| Morton County | 88°F | -11°F |
| Mountrail County | 86°F | -17°F |
| Oliver County | 90°F | -15°F |
| Ransom County | 86°F | -11°F |
| Richland County | 86°F | -13°F |
| Sargent County | 86°F | -11°F |
| Sheridan County | 87°F | -14°F |
| Sioux County | 88°F | -11°F |
| Slope County | 90°F | -12°F |
| Stark County | 90°F | -12°F |
| Steele County | 86°F | -13°F |
| Stutsman County | 87°F | -13°F |
| Traill County | 87°F | -16°F |
| Wells County | 86°F | -13°F |
| Williams County | 90°F | -15°F |
Zone 7: very cold (16 counties, 28% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Benson County | 84°F | -17°F |
| Bottineau County | 88°F | -16°F |
| Burke County | 86°F | -18°F |
| Cavalier County | 86°F | -15°F |
| Divide County | 86°F | -18°F |
| Grand Forks County | 87°F | -16°F |
| McHenry County | 89°F | -13°F |
| Nelson County | 84°F | -17°F |
| Pembina County | 84°F | -17°F |
| Pierce County | 84°F | -18°F |
| Ramsey County | 84°F | -17°F |
| Renville County | 88°F | -16°F |
| Rolette County | 82°F | -17°F |
| Towner County | 84°F | -18°F |
| Walsh County | 84°F | -15°F |
| Ward County | 89°F | -13°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.