Indiana climate zones and HVAC design temperatures
Indiana spans 2 IECC climate zones. 55% of people live in zone 5A (cool, humid). In Indianapolis, heating and cooling equipment is sized for 89°F in summer and 9°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Indianapolis | 4A | 89°F | 9°F | 57°F |
| Fort Wayne | 5A | 88°F | 7°F | 55°F |
| Evansville | 4A | 91°F | 15°F | 60°F |
| South Bend | 5A | 88°F | 6°F | 53°F |
| Bloomington | 4A | 89°F | 10°F | 57°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 (Floyd County); coldest winter design: 4°F (Lake County).
Typical equipment sizes in Indianapolis
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Indianapolis'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 4A: mixed, humid (45 counties, 45% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Bartholomew County | 90°F | 10°F |
| Brown County | 89°F | 10°F |
| Clark County | 91°F | 16°F |
| Clay County | 90°F | 9°F |
| Crawford County | 90°F | 13°F |
| Daviess County | 89°F | 11°F |
| Dearborn County | 89°F | 13°F |
| Decatur County | 90°F | 10°F |
| Dubois County | 90°F | 13°F |
| Fayette County | 90°F | 10°F |
| Floyd County | 92°F | 17°F |
| Franklin County | 89°F | 12°F |
| Gibson County | 91°F | 15°F |
| Greene County | 89°F | 10°F |
| Harrison County | 92°F | 17°F |
| Hendricks County | 89°F | 9°F |
| Jackson County | 89°F | 10°F |
| Jefferson County | 91°F | 16°F |
| Jennings County | 90°F | 10°F |
| Johnson County | 88°F | 9°F |
| Knox County | 91°F | 11°F |
| Lawrence County | 89°F | 10°F |
| Marion County | 89°F | 9°F |
| Martin County | 89°F | 11°F |
| Monroe County | 89°F | 10°F |
| Morgan County | 88°F | 9°F |
| Ohio County | 89°F | 13°F |
| Orange County | 90°F | 13°F |
| Owen County | 89°F | 10°F |
| Perry County | 90°F | 13°F |
| Pike County | 90°F | 13°F |
| Posey County | 90°F | 14°F |
| Putnam County | 90°F | 9°F |
| Ripley County | 89°F | 13°F |
| Rush County | 90°F | 10°F |
| Scott County | 91°F | 16°F |
| Shelby County | 90°F | 10°F |
| Spencer County | 90°F | 13°F |
| Sullivan County | 89°F | 8°F |
| Switzerland County | 89°F | 13°F |
| Union County | 89°F | 12°F |
| Vanderburgh County | 91°F | 15°F |
| Vigo County | 90°F | 9°F |
| Warrick County | 91°F | 15°F |
| Washington County | 91°F | 16°F |
Zone 5A: cool, humid (47 counties, 55% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adams County | 88°F | 7°F |
| Allen County | 88°F | 7°F |
| Benton County | 89°F | 5°F |
| Blackford County | 89°F | 8°F |
| Boone County | 86°F | 6°F |
| Carroll County | 86°F | 5°F |
| Cass County | 86°F | 5°F |
| Clinton County | 86°F | 6°F |
| DeKalb County | 86°F | 9°F |
| Delaware County | 89°F | 8°F |
| Elkhart County | 87°F | 6°F |
| Fountain County | 88°F | 5°F |
| Fulton County | 88°F | 9°F |
| Grant County | 86°F | 7°F |
| Hamilton County | 86°F | 6°F |
| Hancock County | 90°F | 10°F |
| Henry County | 89°F | 8°F |
| Howard County | 88°F | 6°F |
| Huntington County | 88°F | 7°F |
| Jasper County | 86°F | 5°F |
| Jay County | 89°F | 8°F |
| Kosciusko County | 86°F | 5°F |
| LaGrange County | 86°F | 7°F |
| Lake County | 87°F | 4°F |
| LaPorte County | 87°F | 5°F |
| Madison County | 89°F | 8°F |
| Marshall County | 88°F | 9°F |
| Miami County | 88°F | 5°F |
| Montgomery County | 89°F | 5°F |
| Newton County | 86°F | 5°F |
| Noble County | 86°F | 9°F |
| Parke County | 90°F | 9°F |
| Porter County | 88°F | 5°F |
| Pulaski County | 86°F | 5°F |
| Randolph County | 89°F | 8°F |
| St. Joseph County | 88°F | 6°F |
| Starke County | 86°F | 5°F |
| Steuben County | 86°F | 7°F |
| Tippecanoe County | 89°F | 5°F |
| Tipton County | 88°F | 6°F |
| Vermillion County | 89°F | 6°F |
| Wabash County | 88°F | 5°F |
| Warren County | 88°F | 5°F |
| Wayne County | 86°F | 9°F |
| Wells County | 88°F | 7°F |
| White County | 86°F | 5°F |
| Whitley County | 88°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.