Wisconsin climate zones and HVAC design temperatures
Wisconsin spans 2 IECC climate zones. 69% of people live in zone 5A (cool, humid). In Milwaukee, heating and cooling equipment is sized for 87°F in summer and 4°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Milwaukee | 5A | 87°F | 4°F | 53°F |
| Madison | 5A | 86°F | -1°F | 51°F |
| Green Bay | 6A | 86°F | -1°F | 50°F |
| Eau Claire | 6A | 86°F | -8°F | 48°F |
| La Crosse | 5A | 89°F | -3°F | 52°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: 89°F (La Crosse County); coldest winter design: -13°F (Price County).
Typical equipment sizes in Milwaukee
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Milwaukee'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 + 8 kW backup |
| 2,500 sq ft | 3 tons | 60,000 BTU | 3.5 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 5A: cool, humid (30 counties, 69% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adams County | 86°F | -6°F |
| Calumet County | 85°F | -1°F |
| Columbia County | 86°F | -4°F |
| Crawford County | 87°F | -3°F |
| Dane County | 86°F | -1°F |
| Dodge County | 84°F | -3°F |
| Fond du Lac County | 87°F | -1°F |
| Grant County | 86°F | -2°F |
| Green County | 86°F | 1°F |
| Green Lake County | 87°F | -6°F |
| Iowa County | 86°F | 0°F |
| Jefferson County | 85°F | -3°F |
| Juneau County | 86°F | -6°F |
| Kenosha County | 88°F | 2°F |
| La Crosse County | 89°F | -3°F |
| Lafayette County | 86°F | -2°F |
| Milwaukee County | 87°F | 4°F |
| Monroe County | 86°F | -8°F |
| Outagamie County | 86°F | -1°F |
| Ozaukee County | 84°F | 1°F |
| Racine County | 86°F | 3°F |
| Richland County | 87°F | -4°F |
| Rock County | 86°F | 1°F |
| Sauk County | 86°F | -4°F |
| Vernon County | 85°F | -5°F |
| Walworth County | 87°F | 0°F |
| Washington County | 84°F | 1°F |
| Waukesha County | 87°F | 4°F |
| Waushara County | 87°F | -6°F |
| Winnebago County | 85°F | -1°F |
Zone 6A: cold, humid (42 counties, 31% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Ashland County | 84°F | -8°F |
| Barron County | 84°F | -10°F |
| Bayfield County | 84°F | -8°F |
| Brown County | 86°F | -1°F |
| Buffalo County | 86°F | -2°F |
| Burnett County | 84°F | -11°F |
| Chippewa County | 86°F | -8°F |
| Clark County | 84°F | -7°F |
| Door County | 82°F | 0°F |
| Douglas County | 83°F | -10°F |
| Dunn County | 85°F | -8°F |
| Eau Claire County | 86°F | -8°F |
| Florence County | 85°F | -6°F |
| Forest County | 81°F | -10°F |
| Iron County | 82°F | -8°F |
| Jackson County | 87°F | -11°F |
| Kewaunee County | 82°F | 0°F |
| Langlade County | 81°F | -10°F |
| Lincoln County | 83°F | -10°F |
| Manitowoc County | 82°F | 0°F |
| Marathon County | 85°F | -6°F |
| Marinette County | 83°F | -2°F |
| Marquette County | 87°F | -6°F |
| Menominee County | 86°F | -2°F |
| Oconto County | 84°F | -3°F |
| Oneida County | 83°F | -10°F |
| Pepin County | 85°F | -8°F |
| Pierce County | 88°F | -8°F |
| Polk County | 86°F | -8°F |
| Portage County | 84°F | -7°F |
| Price County | 82°F | -13°F |
| Rusk County | 83°F | -10°F |
| Sawyer County | 83°F | -12°F |
| Shawano County | 86°F | -2°F |
| Sheboygan County | 85°F | 0°F |
| St. Croix County | 85°F | -9°F |
| Taylor County | 81°F | -10°F |
| Trempealeau County | 86°F | -2°F |
| Vilas County | 82°F | -10°F |
| Washburn County | 83°F | -12°F |
| Waupaca County | 87°F | 0°F |
| Wood County | 86°F | -6°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.