Mississippi climate zones and HVAC design temperatures
Mississippi spans 2 IECC climate zones. 83% of people live in zone 3A (warm, humid). In Jackson, heating and cooling equipment is sized for 94°F in summer and 29°F in winter.
Design temperatures for major cities
| City | Zone | Summer 1% | Winter 99% | Water in |
|---|---|---|---|---|
| Jackson | 3A | 94°F | 29°F | 69°F |
| Gulfport | 2A | 93°F | 34°F | 72°F |
| Southaven | 3A | 94°F | 24°F | 66°F |
| Hattiesburg | 3A | 94°F | 30°F | 69°F |
| Tupelo | 3A | 94°F | 25°F | 66°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 (Attala County); coldest winter design: 23°F (Alcorn County).
Typical equipment sizes in Jackson
One-story house with average insulation (R-13 walls, R-30 attic, double-pane windows), at Jackson'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 (6 counties, 17% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| George County | 93°F | 32°F |
| Hancock County | 93°F | 34°F |
| Harrison County | 93°F | 34°F |
| Jackson County | 94°F | 32°F |
| Pearl River County | 95°F | 32°F |
| Stone County | 93°F | 34°F |
Zone 3A: warm, humid (76 counties, 83% of people)
| County | Summer 1% | Winter 99% |
|---|---|---|
| Adams County | 93°F | 28°F |
| Alcorn County | 91°F | 23°F |
| Amite County | 93°F | 30°F |
| Attala County | 95°F | 26°F |
| Benton County | 91°F | 23°F |
| Bolivar County | 95°F | 27°F |
| Calhoun County | 91°F | 23°F |
| Carroll County | 95°F | 26°F |
| Chickasaw County | 94°F | 25°F |
| Choctaw County | 93°F | 25°F |
| Claiborne County | 93°F | 28°F |
| Clarke County | 95°F | 28°F |
| Clay County | 94°F | 26°F |
| Coahoma County | 95°F | 28°F |
| Copiah County | 94°F | 29°F |
| Covington County | 94°F | 28°F |
| DeSoto County | 94°F | 24°F |
| Forrest County | 94°F | 30°F |
| Franklin County | 93°F | 28°F |
| Greene County | 94°F | 30°F |
| Grenada County | 95°F | 26°F |
| Hinds County | 94°F | 29°F |
| Holmes County | 95°F | 26°F |
| Humphreys County | 95°F | 26°F |
| Issaquena County | 95°F | 28°F |
| Itawamba County | 94°F | 25°F |
| Jasper County | 93°F | 29°F |
| Jefferson County | 93°F | 28°F |
| Jefferson Davis County | 94°F | 28°F |
| Jones County | 93°F | 29°F |
| Kemper County | 94°F | 28°F |
| Lafayette County | 91°F | 23°F |
| Lamar County | 94°F | 30°F |
| Lauderdale County | 95°F | 28°F |
| Lawrence County | 93°F | 30°F |
| Leake County | 95°F | 28°F |
| Lee County | 94°F | 25°F |
| Leflore County | 95°F | 26°F |
| Lincoln County | 93°F | 30°F |
| Lowndes County | 94°F | 26°F |
| Madison County | 95°F | 28°F |
| Marion County | 95°F | 32°F |
| Marshall County | 91°F | 23°F |
| Monroe County | 94°F | 26°F |
| Montgomery County | 95°F | 26°F |
| Neshoba County | 94°F | 28°F |
| Newton County | 95°F | 28°F |
| Noxubee County | 94°F | 26°F |
| Oktibbeha County | 93°F | 25°F |
| Panola County | 91°F | 23°F |
| Perry County | 94°F | 30°F |
| Pike County | 93°F | 30°F |
| Pontotoc County | 94°F | 25°F |
| Prentiss County | 91°F | 23°F |
| Quitman County | 95°F | 28°F |
| Rankin County | 95°F | 28°F |
| Scott County | 95°F | 28°F |
| Sharkey County | 95°F | 27°F |
| Simpson County | 95°F | 28°F |
| Smith County | 93°F | 29°F |
| Sunflower County | 95°F | 27°F |
| Tallahatchie County | 95°F | 28°F |
| Tate County | 93°F | 23°F |
| Tippah County | 91°F | 23°F |
| Tishomingo County | 91°F | 23°F |
| Tunica County | 93°F | 23°F |
| Union County | 94°F | 25°F |
| Walthall County | 93°F | 30°F |
| Warren County | 93°F | 28°F |
| Washington County | 95°F | 27°F |
| Wayne County | 93°F | 29°F |
| Webster County | 93°F | 25°F |
| Wilkinson County | 92°F | 32°F |
| Winston County | 93°F | 25°F |
| Yalobusha County | 91°F | 23°F |
| Yazoo County | 94°F | 29°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.