Ohio climate zones and HVAC design temperatures
Ohio spans 2 IECC climate zones. 67% of people live in zone 5A (cool, humid). In Columbus, heating and cooling equipment is sized for 89°F in summer and 11°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Columbus | 4A | 89°F | 11°F | 57°F |
| Cleveland | 5A | 86°F | 12°F | 56°F |
| Cincinnati | 4A | 89°F | 14°F | 58°F |
| Toledo | 5A | 87°F | 9°F | 53°F |
| Dayton | 5A | 88°F | 10°F | 56°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: 90°F (Preble County); coldest winter design: 6°F (Holmes County).
Typical equipment sizes in Columbus
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Columbus'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 + 5 kW backup |
| 2,000 sq ft | 2.5 tons | 40,000 BTU | 3 tons + 5 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 (24 counties, 33% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adams County | 89°F | 15°F |
| Athens County | 89°F | 11°F |
| Brown County | 89°F | 15°F |
| Butler County | 89°F | 12°F |
| Clermont County | 89°F | 14°F |
| Clinton County | 87°F | 10°F |
| Fayette County | 87°F | 10°F |
| Franklin County | 89°F | 11°F |
| Gallia County | 89°F | 11°F |
| Greene County | 88°F | 10°F |
| Hamilton County | 89°F | 14°F |
| Highland County | 87°F | 10°F |
| Hocking County | 88°F | 10°F |
| Jackson County | 89°F | 11°F |
| Lawrence County | 89°F | 15°F |
| Madison County | 89°F | 10°F |
| Meigs County | 89°F | 11°F |
| Pickaway County | 88°F | 10°F |
| Pike County | 89°F | 15°F |
| Ross County | 88°F | 10°F |
| Scioto County | 89°F | 15°F |
| Vinton County | 89°F | 11°F |
| Warren County | 90°F | 12°F |
| Washington County | 88°F | 12°F |
Zone 5A: cool, humid (64 counties, 67% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Allen County | 87°F | 8°F |
| Ashland County | 87°F | 8°F |
| Ashtabula County | 85°F | 9°F |
| Auglaize County | 87°F | 8°F |
| Belmont County | 86°F | 11°F |
| Carroll County | 88°F | 9°F |
| Champaign County | 87°F | 9°F |
| Clark County | 87°F | 9°F |
| Columbiana County | 86°F | 7°F |
| Coshocton County | 88°F | 11°F |
| Crawford County | 87°F | 7°F |
| Cuyahoga County | 86°F | 12°F |
| Darke County | 86°F | 9°F |
| Defiance County | 88°F | 7°F |
| Delaware County | 88°F | 10°F |
| Erie County | 86°F | 8°F |
| Fairfield County | 88°F | 10°F |
| Fulton County | 89°F | 7°F |
| Geauga County | 85°F | 7°F |
| Guernsey County | 88°F | 11°F |
| Hancock County | 89°F | 8°F |
| Hardin County | 87°F | 8°F |
| Harrison County | 88°F | 9°F |
| Henry County | 88°F | 7°F |
| Holmes County | 86°F | 6°F |
| Huron County | 87°F | 8°F |
| Jefferson County | 86°F | 11°F |
| Knox County | 89°F | 10°F |
| Lake County | 86°F | 12°F |
| Licking County | 89°F | 10°F |
| Logan County | 87°F | 7°F |
| Lorain County | 86°F | 8°F |
| Lucas County | 87°F | 9°F |
| Mahoning County | 86°F | 8°F |
| Marion County | 87°F | 7°F |
| Medina County | 88°F | 10°F |
| Mercer County | 86°F | 9°F |
| Miami County | 88°F | 10°F |
| Monroe County | 88°F | 12°F |
| Montgomery County | 88°F | 10°F |
| Morgan County | 88°F | 11°F |
| Morrow County | 87°F | 7°F |
| Muskingum County | 88°F | 11°F |
| Noble County | 88°F | 11°F |
| Ottawa County | 89°F | 8°F |
| Paulding County | 88°F | 7°F |
| Perry County | 89°F | 10°F |
| Portage County | 85°F | 7°F |
| Preble County | 90°F | 12°F |
| Putnam County | 87°F | 8°F |
| Richland County | 87°F | 8°F |
| Sandusky County | 89°F | 8°F |
| Seneca County | 89°F | 8°F |
| Shelby County | 86°F | 9°F |
| Stark County | 87°F | 9°F |
| Summit County | 89°F | 10°F |
| Trumbull County | 86°F | 8°F |
| Tuscarawas County | 88°F | 9°F |
| Union County | 87°F | 7°F |
| Van Wert County | 87°F | 8°F |
| Wayne County | 86°F | 6°F |
| Williams County | 88°F | 7°F |
| Wood County | 89°F | 8°F |
| Wyandot County | 87°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.