South Dakota climate zones and HVAC design temperatures
South Dakota spans 2 IECC climate zones. 86% of people live in zone 6A (cold, humid). In Sioux Falls, heating and cooling equipment is sized for 90°F in summer and -4°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Sioux Falls | 6A | 90°F | -4°F | 51°F |
| Rapid City | 6A | 92°F | -3°F | 49°F |
| Aberdeen | 6A | 90°F | -10°F | 48°F |
| Brookings | 6A | 87°F | -9°F | 47°F |
| Pierre | 6A | 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: 96°F (Haakon County); coldest winter design: -10°F (Brown County).
Typical equipment sizes in Sioux Falls
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Sioux Falls'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 + 10 kW backup |
| 2,000 sq ft | 2.5 tons | 60,000 BTU | 3 tons + 10 kW backup |
| 2,500 sq ft | 3 tons | 60,000 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 5A: cool, humid (18 counties, 14% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Bennett County | 95°F | -3°F |
| Bon Homme County | 91°F | -3°F |
| Brule County | 91°F | -3°F |
| Charles Mix County | 91°F | -4°F |
| Clay County | 91°F | -3°F |
| Douglas County | 91°F | -4°F |
| Gregory County | 94°F | -2°F |
| Haakon County | 96°F | -5°F |
| Hutchinson County | 91°F | -4°F |
| Jackson County | 96°F | -5°F |
| Jones County | 93°F | -5°F |
| Lyman County | 91°F | -3°F |
| Mellette County | 95°F | -2°F |
| Stanley County | 93°F | -5°F |
| Todd County | 95°F | -2°F |
| Tripp County | 94°F | -2°F |
| Union County | 91°F | -4°F |
| Yankton County | 91°F | -3°F |
Zone 6A: cold, humid (48 counties, 86% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Aurora County | 91°F | -4°F |
| Beadle County | 90°F | -7°F |
| Brookings County | 87°F | -9°F |
| Brown County | 90°F | -10°F |
| Buffalo County | 91°F | -3°F |
| Butte County | 90°F | -4°F |
| Campbell County | 92°F | -7°F |
| Clark County | 87°F | -10°F |
| Codington County | 87°F | -10°F |
| Corson County | 92°F | -7°F |
| Custer County | 85°F | -2°F |
| Davison County | 91°F | -4°F |
| Day County | 88°F | -9°F |
| Deuel County | 90°F | -5°F |
| Dewey County | 92°F | -7°F |
| Edmunds County | 90°F | -10°F |
| Fall River County | 85°F | -2°F |
| Faulk County | 90°F | -10°F |
| Grant County | 88°F | -9°F |
| Hamlin County | 87°F | -10°F |
| Hand County | 90°F | -7°F |
| Hanson County | 91°F | -4°F |
| Harding County | 93°F | -6°F |
| Hughes County | 93°F | -5°F |
| Hyde County | 93°F | -5°F |
| Jerauld County | 90°F | -7°F |
| Kingsbury County | 86°F | -8°F |
| Lake County | 86°F | -8°F |
| Lawrence County | 90°F | -4°F |
| Lincoln County | 90°F | -4°F |
| Marshall County | 88°F | -9°F |
| McCook County | 86°F | -8°F |
| McPherson County | 90°F | -10°F |
| Meade County | 93°F | -2°F |
| Miner County | 86°F | -8°F |
| Minnehaha County | 90°F | -4°F |
| Moody County | 87°F | -9°F |
| Oglala Lakota County | 95°F | -3°F |
| Pennington County | 92°F | -3°F |
| Perkins County | 91°F | -10°F |
| Potter County | 92°F | -7°F |
| Roberts County | 88°F | -9°F |
| Sanborn County | 91°F | -4°F |
| Spink County | 90°F | -10°F |
| Sully County | 93°F | -5°F |
| Turner County | 90°F | -4°F |
| Walworth County | 92°F | -7°F |
| Ziebach County | 92°F | -7°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.