Georgia climate zones and HVAC design temperatures
Georgia spans 2 IECC climate zones. 86% of people live in zone 3A (warm, humid). In Atlanta, heating and cooling equipment is sized for 92°F in summer and 27°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Atlanta | 3A | 92°F | 27°F | 65°F |
| Columbus | 3A | 94°F | 31°F | 69°F |
| Augusta | 3A | 95°F | 33°F | 69°F |
| Macon | 3A | 95°F | 28°F | 68°F |
| Savannah | 2A | 93°F | 34°F | 70°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: 95°F (Baker County); coldest winter design: 25°F (Bartow County).
Typical equipment sizes in Atlanta
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Atlanta'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 |
| 2,000 sq ft | 3 tons | 40,000 BTU | 3 tons |
| 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 2A: hot, humid (41 counties, 14% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Appling County | 94°F | 32°F |
| Atkinson County | 93°F | 34°F |
| Bacon County | 94°F | 32°F |
| Baker County | 95°F | 32°F |
| Berrien County | 94°F | 34°F |
| Brantley County | 95°F | 34°F |
| Brooks County | 94°F | 33°F |
| Bryan County | 93°F | 34°F |
| Calhoun County | 93°F | 32°F |
| Camden County | 91°F | 39°F |
| Charlton County | 93°F | 36°F |
| Chatham County | 93°F | 34°F |
| Clinch County | 94°F | 32°F |
| Coffee County | 93°F | 34°F |
| Colquitt County | 91°F | 34°F |
| Cook County | 94°F | 34°F |
| Decatur County | 95°F | 34°F |
| Dougherty County | 95°F | 32°F |
| Early County | 93°F | 32°F |
| Echols County | 94°F | 33°F |
| Effingham County | 94°F | 33°F |
| Evans County | 94°F | 31°F |
| Glynn County | 92°F | 34°F |
| Grady County | 91°F | 34°F |
| Jeff Davis County | 94°F | 34°F |
| Lanier County | 94°F | 34°F |
| Liberty County | 94°F | 32°F |
| Long County | 94°F | 32°F |
| Lowndes County | 94°F | 33°F |
| McIntosh County | 92°F | 34°F |
| Miller County | 95°F | 34°F |
| Mitchell County | 95°F | 32°F |
| Pierce County | 95°F | 34°F |
| Seminole County | 95°F | 34°F |
| Tattnall County | 94°F | 31°F |
| Thomas County | 91°F | 34°F |
| Tift County | 94°F | 33°F |
| Toombs County | 95°F | 34°F |
| Ware County | 95°F | 34°F |
| Wayne County | 94°F | 32°F |
| Worth County | 95°F | 32°F |
Zone 3A: warm, humid (118 counties, 86% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Baldwin County | 93°F | 30°F |
| Banks County | 90°F | 28°F |
| Barrow County | 91°F | 30°F |
| Bartow County | 92°F | 25°F |
| Ben Hill County | 94°F | 33°F |
| Bibb County | 95°F | 28°F |
| Bleckley County | 94°F | 29°F |
| Bulloch County | 93°F | 31°F |
| Burke County | 95°F | 28°F |
| Butts County | 91°F | 30°F |
| Candler County | 94°F | 31°F |
| Carroll County | 89°F | 26°F |
| Catoosa County | 93°F | 26°F |
| Chattahoochee County | 94°F | 27°F |
| Chattooga County | 93°F | 25°F |
| Cherokee County | 91°F | 28°F |
| Clarke County | 93°F | 28°F |
| Clay County | 93°F | 32°F |
| Clayton County | 92°F | 29°F |
| Cobb County | 91°F | 27°F |
| Columbia County | 95°F | 33°F |
| Coweta County | 92°F | 30°F |
| Crawford County | 95°F | 28°F |
| Crisp County | 95°F | 32°F |
| Dade County | 93°F | 26°F |
| Dawson County | 90°F | 28°F |
| DeKalb County | 92°F | 27°F |
| Dodge County | 94°F | 29°F |
| Dooly County | 95°F | 32°F |
| Douglas County | 92°F | 28°F |
| Elbert County | 93°F | 28°F |
| Emanuel County | 95°F | 32°F |
| Fannin County | 91°F | 25°F |
| Fayette County | 92°F | 27°F |
| Floyd County | 93°F | 25°F |
| Forsyth County | 91°F | 28°F |
| Franklin County | 93°F | 29°F |
| Fulton County | 92°F | 27°F |
| Gilmer County | 91°F | 25°F |
| Glascock County | 94°F | 28°F |
| Gordon County | 91°F | 25°F |
| Greene County | 93°F | 30°F |
| Gwinnett County | 92°F | 27°F |
| Habersham County | 93°F | 29°F |
| Hall County | 90°F | 28°F |
| Hancock County | 93°F | 30°F |
| Haralson County | 89°F | 26°F |
| Harris County | 94°F | 31°F |
| Hart County | 93°F | 28°F |
| Heard County | 92°F | 30°F |
| Henry County | 91°F | 30°F |
| Houston County | 94°F | 30°F |
| Irwin County | 94°F | 33°F |
| Jackson County | 90°F | 28°F |
| Jasper County | 91°F | 30°F |
| Jefferson County | 95°F | 32°F |
| Jenkins County | 94°F | 31°F |
| Johnson County | 95°F | 32°F |
| Jones County | 95°F | 28°F |
| Lamar County | 91°F | 30°F |
| Laurens County | 95°F | 30°F |
| Lee County | 95°F | 32°F |
| Lincoln County | 94°F | 28°F |
| Lumpkin County | 90°F | 28°F |
| Macon County | 95°F | 32°F |
| Madison County | 93°F | 28°F |
| Marion County | 94°F | 31°F |
| McDuffie County | 94°F | 28°F |
| Meriwether County | 92°F | 30°F |
| Monroe County | 91°F | 30°F |
| Montgomery County | 95°F | 34°F |
| Morgan County | 93°F | 30°F |
| Murray County | 91°F | 25°F |
| Muscogee County | 94°F | 31°F |
| Newton County | 92°F | 27°F |
| Oconee County | 93°F | 28°F |
| Oglethorpe County | 93°F | 28°F |
| Paulding County | 91°F | 28°F |
| Peach County | 95°F | 28°F |
| Pickens County | 91°F | 28°F |
| Pike County | 91°F | 30°F |
| Polk County | 91°F | 28°F |
| Pulaski County | 94°F | 29°F |
| Putnam County | 93°F | 30°F |
| Quitman County | 95°F | 30°F |
| Rabun County | 93°F | 29°F |
| Randolph County | 95°F | 30°F |
| Richmond County | 95°F | 33°F |
| Rockdale County | 92°F | 27°F |
| Schley County | 95°F | 32°F |
| Screven County | 94°F | 31°F |
| Spalding County | 91°F | 30°F |
| Stephens County | 93°F | 29°F |
| Stewart County | 94°F | 27°F |
| Sumter County | 95°F | 32°F |
| Talbot County | 94°F | 31°F |
| Taliaferro County | 93°F | 30°F |
| Taylor County | 91°F | 30°F |
| Telfair County | 94°F | 34°F |
| Terrell County | 95°F | 32°F |
| Towns County | 93°F | 29°F |
| Treutlen County | 95°F | 34°F |
| Troup County | 93°F | 27°F |
| Turner County | 94°F | 33°F |
| Twiggs County | 94°F | 30°F |
| Union County | 90°F | 28°F |
| Upson County | 91°F | 30°F |
| Walker County | 93°F | 26°F |
| Walton County | 91°F | 30°F |
| Warren County | 94°F | 28°F |
| Washington County | 95°F | 30°F |
| Webster County | 95°F | 32°F |
| Wheeler County | 94°F | 34°F |
| White County | 90°F | 28°F |
| Whitfield County | 91°F | 25°F |
| Wilcox County | 94°F | 33°F |
| Wilkes County | 94°F | 28°F |
| Wilkinson County | 95°F | 30°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.