Oklahoma climate zones and HVAC design temperatures
Oklahoma spans 3 IECC climate zones. 90% of people live in zone 3A (warm, humid). In Oklahoma City, heating and cooling equipment is sized for 97°F in summer and 19°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Oklahoma City | 3A | 97°F | 19°F | 64°F |
| Tulsa | 3A | 97°F | 19°F | 64°F |
| Norman | 3A | 96°F | 19°F | 64°F |
| Lawton | 3A | 99°F | 21°F | 64°F |
| Enid | 4A | 98°F | 16°F | 62°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: 102°F (Tillman County); coldest winter design: 9°F (Cimarron County).
Typical equipment sizes in Oklahoma City
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Oklahoma City'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 | 2.5 tons | 40,000 BTU | 2.5 tons + 5 kW backup |
| 2,000 sq ft | 3 tons | 40,000 BTU | 3 tons + 5 kW backup |
| 2,500 sq ft | 3.5 tons | 40,000 BTU | 3.5 tons + 5 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 3A: warm, humid (59 counties, 90% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adair County | 95°F | 18°F |
| Atoka County | 99°F | 27°F |
| Beckham County | 97°F | 17°F |
| Blaine County | 98°F | 17°F |
| Bryan County | 99°F | 27°F |
| Caddo County | 98°F | 19°F |
| Canadian County | 97°F | 18°F |
| Carter County | 97°F | 23°F |
| Cherokee County | 95°F | 18°F |
| Choctaw County | 97°F | 25°F |
| Cleveland County | 96°F | 19°F |
| Coal County | 95°F | 21°F |
| Comanche County | 99°F | 21°F |
| Cotton County | 101°F | 20°F |
| Creek County | 97°F | 19°F |
| Custer County | 98°F | 18°F |
| Dewey County | 97°F | 14°F |
| Garvin County | 96°F | 20°F |
| Grady County | 98°F | 19°F |
| Greer County | 101°F | 21°F |
| Harmon County | 100°F | 21°F |
| Haskell County | 99°F | 21°F |
| Hughes County | 95°F | 21°F |
| Jackson County | 101°F | 21°F |
| Jefferson County | 99°F | 21°F |
| Johnston County | 99°F | 21°F |
| Kingfisher County | 97°F | 18°F |
| Kiowa County | 101°F | 19°F |
| Latimer County | 99°F | 21°F |
| Le Flore County | 96°F | 21°F |
| Lincoln County | 95°F | 18°F |
| Logan County | 97°F | 18°F |
| Love County | 97°F | 23°F |
| Marshall County | 99°F | 27°F |
| Mayes County | 93°F | 18°F |
| McClain County | 96°F | 18°F |
| McCurtain County | 95°F | 25°F |
| McIntosh County | 94°F | 19°F |
| Murray County | 99°F | 21°F |
| Muskogee County | 94°F | 19°F |
| Noble County | 98°F | 17°F |
| Okfuskee County | 96°F | 19°F |
| Oklahoma County | 97°F | 19°F |
| Okmulgee County | 96°F | 19°F |
| Pawnee County | 96°F | 21°F |
| Payne County | 98°F | 17°F |
| Pittsburg County | 96°F | 21°F |
| Pontotoc County | 95°F | 21°F |
| Pottawatomie County | 96°F | 19°F |
| Pushmataha County | 96°F | 21°F |
| Roger Mills County | 97°F | 17°F |
| Rogers County | 93°F | 18°F |
| Seminole County | 96°F | 19°F |
| Sequoyah County | 97°F | 21°F |
| Stephens County | 99°F | 21°F |
| Tillman County | 102°F | 21°F |
| Tulsa County | 97°F | 19°F |
| Wagoner County | 96°F | 19°F |
| Washita County | 99°F | 17°F |
Zone 4A: mixed, humid (15 counties, 9% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Alfalfa County | 100°F | 14°F |
| Craig County | 93°F | 18°F |
| Delaware County | 93°F | 18°F |
| Ellis County | 99°F | 14°F |
| Garfield County | 98°F | 16°F |
| Grant County | 98°F | 16°F |
| Harper County | 97°F | 14°F |
| Kay County | 97°F | 16°F |
| Major County | 98°F | 16°F |
| Nowata County | 95°F | 15°F |
| Osage County | 96°F | 21°F |
| Ottawa County | 93°F | 18°F |
| Washington County | 95°F | 15°F |
| Woods County | 100°F | 14°F |
| Woodward County | 97°F | 14°F |
Zone 4B: mixed, dry (3 counties, 1% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Beaver County | 98°F | 12°F |
| Cimarron County | 95°F | 9°F |
| Texas County | 99°F | 14°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.