Michigan climate zones and HVAC design temperatures
Michigan spans 3 IECC climate zones. 89% of people live in zone 5A (cool, humid). In Detroit, heating and cooling equipment is sized for 88°F in summer and 9°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Detroit | 5A | 88°F | 9°F | 55°F |
| Grand Rapids | 5A | 87°F | 8°F | 52°F |
| Lansing | 5A | 87°F | 7°F | 52°F |
| Ann Arbor | 5A | 86°F | 5°F | 52°F |
| Marquette | 7 | 81°F | 2°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: 88°F (Cass County); coldest winter design: -11°F (Ontonagon County).
Typical equipment sizes in Detroit
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Detroit'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 | 40,000 BTU | 3 tons + 8 kW backup |
| 2,500 sq ft | 3 tons | 60,000 BTU | 3.5 tons + 8 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 (37 counties, 89% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Allegan County | 86°F | 11°F |
| Barry County | 87°F | 8°F |
| Bay County | 86°F | 6°F |
| Berrien County | 87°F | 10°F |
| Branch County | 86°F | 7°F |
| Calhoun County | 87°F | 8°F |
| Cass County | 88°F | 6°F |
| Clinton County | 87°F | 7°F |
| Eaton County | 86°F | 6°F |
| Genesee County | 87°F | 7°F |
| Gratiot County | 86°F | 5°F |
| Hillsdale County | 85°F | 6°F |
| Huron County | 84°F | 4°F |
| Ingham County | 87°F | 7°F |
| Ionia County | 86°F | 8°F |
| Jackson County | 86°F | 6°F |
| Kalamazoo County | 88°F | 8°F |
| Kent County | 87°F | 8°F |
| Lapeer County | 87°F | 5°F |
| Lenawee County | 87°F | 6°F |
| Livingston County | 86°F | 6°F |
| Macomb County | 86°F | 8°F |
| Midland County | 87°F | 5°F |
| Monroe County | 87°F | 8°F |
| Montcalm County | 86°F | 5°F |
| Muskegon County | 85°F | 11°F |
| Oakland County | 86°F | 6°F |
| Ottawa County | 86°F | 11°F |
| Saginaw County | 86°F | 7°F |
| Sanilac County | 84°F | 4°F |
| Shiawassee County | 86°F | 6°F |
| St. Clair County | 84°F | 5°F |
| St. Joseph County | 87°F | 7°F |
| Tuscola County | 86°F | 4°F |
| Van Buren County | 85°F | 11°F |
| Washtenaw County | 86°F | 5°F |
| Wayne County | 88°F | 9°F |
Zone 6A: cold, humid (44 counties, 11% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Alcona County | 85°F | 2°F |
| Alger County | 81°F | 2°F |
| Alpena County | 85°F | 2°F |
| Antrim County | 85°F | 5°F |
| Arenac County | 87°F | 5°F |
| Baraga County | 82°F | 1°F |
| Benzie County | 81°F | 9°F |
| Charlevoix County | 82°F | 7°F |
| Cheboygan County | 82°F | 1°F |
| Chippewa County | 82°F | -3°F |
| Clare County | 87°F | 6°F |
| Crawford County | 85°F | -2°F |
| Delta County | 80°F | -2°F |
| Dickinson County | 85°F | -6°F |
| Emmet County | 81°F | 3°F |
| Gladwin County | 87°F | 5°F |
| Gogebic County | 82°F | -8°F |
| Grand Traverse County | 86°F | 8°F |
| Houghton County | 82°F | 1°F |
| Iosco County | 85°F | 2°F |
| Iron County | 85°F | -6°F |
| Isabella County | 87°F | 6°F |
| Kalkaska County | 85°F | 5°F |
| Lake County | 85°F | 5°F |
| Leelanau County | 86°F | 8°F |
| Luce County | 81°F | -1°F |
| Mackinac County | 77°F | 3°F |
| Manistee County | 83°F | 8°F |
| Mason County | 81°F | 10°F |
| Mecosta County | 85°F | 5°F |
| Menominee County | 83°F | -2°F |
| Missaukee County | 84°F | 2°F |
| Montmorency County | 84°F | 1°F |
| Newaygo County | 85°F | 8°F |
| Oceana County | 85°F | 8°F |
| Ogemaw County | 84°F | 2°F |
| Ontonagon County | 82°F | -11°F |
| Osceola County | 85°F | 5°F |
| Oscoda County | 85°F | -2°F |
| Otsego County | 84°F | 1°F |
| Presque Isle County | 82°F | 4°F |
| Roscommon County | 84°F | 2°F |
| Schoolcraft County | 77°F | -1°F |
| Wexford County | 84°F | 2°F |
Zone 7: very cold (2 counties, 1% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Keweenaw County | 82°F | 1°F |
| Marquette County | 81°F | 2°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.