South Carolina climate zones and HVAC design temperatures
South Carolina spans 2 IECC climate zones. 96% of people live in zone 3A (warm, humid). In Charleston, heating and cooling equipment is sized for 92°F in summer and 32°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Charleston | 3A | 92°F | 32°F | 69°F |
| Columbia | 3A | 95°F | 30°F | 68°F |
| Greenville | 3A | 92°F | 29°F | 66°F |
| Myrtle Beach | 3A | 91°F | 28°F | 65°F |
| Florence | 3A | 94°F | 28°F | 67°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 (Allendale County); coldest winter design: 24°F (Pickens County).
Typical equipment sizes in Charleston
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Charleston'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 |
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 (2 counties, 4% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Beaufort County | 91°F | 36°F |
| Jasper County | 94°F | 34°F |
Zone 3A: warm, humid (44 counties, 96% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Abbeville County | 92°F | 26°F |
| Aiken County | 93°F | 28°F |
| Allendale County | 95°F | 28°F |
| Anderson County | 93°F | 28°F |
| Bamberg County | 95°F | 28°F |
| Barnwell County | 95°F | 28°F |
| Berkeley County | 91°F | 30°F |
| Calhoun County | 93°F | 30°F |
| Charleston County | 92°F | 32°F |
| Cherokee County | 91°F | 28°F |
| Chester County | 93°F | 27°F |
| Chesterfield County | 93°F | 27°F |
| Clarendon County | 91°F | 28°F |
| Colleton County | 91°F | 30°F |
| Darlington County | 91°F | 28°F |
| Dillon County | 91°F | 28°F |
| Dorchester County | 93°F | 30°F |
| Edgefield County | 93°F | 28°F |
| Fairfield County | 91°F | 30°F |
| Florence County | 94°F | 28°F |
| Georgetown County | 90°F | 30°F |
| Greenville County | 92°F | 29°F |
| Greenwood County | 92°F | 26°F |
| Hampton County | 91°F | 30°F |
| Horry County | 91°F | 28°F |
| Kershaw County | 93°F | 27°F |
| Lancaster County | 93°F | 27°F |
| Laurens County | 91°F | 28°F |
| Lee County | 95°F | 28°F |
| Lexington County | 95°F | 29°F |
| Marion County | 91°F | 28°F |
| Marlboro County | 95°F | 28°F |
| McCormick County | 92°F | 26°F |
| Newberry County | 91°F | 30°F |
| Oconee County | 92°F | 29°F |
| Orangeburg County | 93°F | 30°F |
| Pickens County | 92°F | 24°F |
| Richland County | 95°F | 30°F |
| Saluda County | 93°F | 28°F |
| Spartanburg County | 91°F | 28°F |
| Sumter County | 95°F | 28°F |
| Union County | 91°F | 28°F |
| Williamsburg County | 91°F | 28°F |
| York County | 92°F | 25°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.