BTU sizing chart by square feet and climate zone
Cooling and heating load for common house sizes, in every DOE climate zone. All figures assume 8 ft ceilings, average insulation, average sun and two occupants, so they are a starting point rather than an answer for a particular building.
Change any of those assumptions in the calculator, which uses the same module that generated every number on this page.
Before you buy anything. This is a square-foot estimate, not an ACCA Manual J load calculation. A Manual J uses your building’s real construction, orientation and air leakage, and on a well-sealed house it usually comes out smaller than this. Use this to sanity-check a quote, not to replace one.
Climate zone 1: hot humid
Miami, Key West, Honolulu. Cooling 30 to 35 BTU per sq ft, heating 15 to 25.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 15,938 | 9,375 | 18,000 | 1.5 |
| 600 | 19,125 | 11,250 | 24,000 | 2.0 |
| 800 | 25,500 | 15,000 | 30,000 | 2.5 |
| 1,000 | 31,875 | 18,750 | 36,000 | 3.0 |
| 1,200 | 38,250 | 22,500 | 42,000 | 3.5 |
| 1,500 | 47,813 | 28,125 | 48,000 | 4.0 |
| 1,600 | 51,000 | 30,000 | 54,000 | 4.5 |
| 1,800 | 57,375 | 33,750 | 60,000 | 5.0 |
| 2,000 | 63,750 | 37,500 | 60,000 | 5.0 |
| 2,500 | 79,688 | 46,875 | 60,000 | 5.0 |
| 3,000 | 95,625 | 56,250 | 60,000 | 5.0 |
| 3,500 | 111,563 | 65,625 | 60,000 | 5.0 |
| 4,000 | 127,500 | 75,000 | 60,000 | 5.0 |
Climate zone 2: hot
Houston, Orlando, Phoenix, New Orleans. Cooling 27 to 30 BTU per sq ft, heating 20 to 30.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 14,063 | 11,875 | 18,000 | 1.5 |
| 600 | 16,875 | 14,250 | 18,000 | 1.5 |
| 800 | 22,500 | 19,000 | 24,000 | 2.0 |
| 1,000 | 28,125 | 23,750 | 30,000 | 2.5 |
| 1,200 | 33,750 | 28,500 | 36,000 | 3.0 |
| 1,500 | 42,188 | 35,625 | 48,000 | 4.0 |
| 1,600 | 45,000 | 38,000 | 48,000 | 4.0 |
| 1,800 | 50,625 | 42,750 | 54,000 | 4.5 |
| 2,000 | 56,250 | 47,500 | 60,000 | 5.0 |
| 2,500 | 70,313 | 59,375 | 60,000 | 5.0 |
| 3,000 | 84,375 | 71,250 | 60,000 | 5.0 |
| 3,500 | 98,438 | 83,125 | 60,000 | 5.0 |
| 4,000 | 112,500 | 95,000 | 60,000 | 5.0 |
Climate zone 3: warm
Atlanta, Dallas, Los Angeles, Charlotte. Cooling 24 to 27 BTU per sq ft, heating 25 to 35.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 12,563 | 14,375 | 18,000 | 1.5 |
| 600 | 15,075 | 17,250 | 18,000 | 1.5 |
| 800 | 20,100 | 23,000 | 24,000 | 2.0 |
| 1,000 | 25,125 | 28,750 | 30,000 | 2.5 |
| 1,200 | 30,150 | 34,500 | 36,000 | 3.0 |
| 1,500 | 37,688 | 43,125 | 42,000 | 3.5 |
| 1,600 | 40,200 | 46,000 | 42,000 | 3.5 |
| 1,800 | 45,225 | 51,750 | 48,000 | 4.0 |
| 2,000 | 50,250 | 57,500 | 54,000 | 4.5 |
| 2,500 | 62,813 | 71,875 | 60,000 | 5.0 |
| 3,000 | 75,375 | 86,250 | 60,000 | 5.0 |
| 3,500 | 87,938 | 100,625 | 60,000 | 5.0 |
| 4,000 | 100,500 | 115,000 | 60,000 | 5.0 |
Climate zone 4: mixed
Washington DC, Seattle, St Louis, Nashville. Cooling 22 to 25 BTU per sq ft, heating 30 to 40.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 11,563 | 16,875 | 18,000 | 1.5 |
| 600 | 13,875 | 20,250 | 18,000 | 1.5 |
| 800 | 18,500 | 27,000 | 24,000 | 2.0 |
| 1,000 | 23,125 | 33,750 | 24,000 | 2.0 |
| 1,200 | 27,750 | 40,500 | 30,000 | 2.5 |
| 1,500 | 34,688 | 50,625 | 36,000 | 3.0 |
| 1,600 | 37,000 | 54,000 | 42,000 | 3.5 |
| 1,800 | 41,625 | 60,750 | 42,000 | 3.5 |
| 2,000 | 46,250 | 67,500 | 48,000 | 4.0 |
| 2,500 | 57,813 | 84,375 | 60,000 | 5.0 |
| 3,000 | 69,375 | 101,250 | 60,000 | 5.0 |
| 3,500 | 80,938 | 118,125 | 60,000 | 5.0 |
| 4,000 | 92,500 | 135,000 | 60,000 | 5.0 |
Climate zone 5: cool
Chicago, Denver, Boston, Detroit. Cooling 20 to 23 BTU per sq ft, heating 35 to 45.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 10,563 | 19,375 | 18,000 | 1.5 |
| 600 | 12,675 | 23,250 | 18,000 | 1.5 |
| 800 | 16,900 | 31,000 | 18,000 | 1.5 |
| 1,000 | 21,125 | 38,750 | 24,000 | 2.0 |
| 1,200 | 25,350 | 46,500 | 30,000 | 2.5 |
| 1,500 | 31,688 | 58,125 | 36,000 | 3.0 |
| 1,600 | 33,800 | 62,000 | 36,000 | 3.0 |
| 1,800 | 38,025 | 69,750 | 42,000 | 3.5 |
| 2,000 | 42,250 | 77,500 | 48,000 | 4.0 |
| 2,500 | 52,813 | 96,875 | 54,000 | 4.5 |
| 3,000 | 63,375 | 116,250 | 60,000 | 5.0 |
| 3,500 | 73,938 | 135,625 | 60,000 | 5.0 |
| 4,000 | 84,500 | 155,000 | 60,000 | 5.0 |
Climate zone 6: cold
Minneapolis, Burlington, Helena. Cooling 18 to 22 BTU per sq ft, heating 40 to 50.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 9,750 | 21,875 | 18,000 | 1.5 |
| 600 | 11,700 | 26,250 | 18,000 | 1.5 |
| 800 | 15,600 | 35,000 | 18,000 | 1.5 |
| 1,000 | 19,500 | 43,750 | 24,000 | 2.0 |
| 1,200 | 23,400 | 52,500 | 24,000 | 2.0 |
| 1,500 | 29,250 | 65,625 | 30,000 | 2.5 |
| 1,600 | 31,200 | 70,000 | 36,000 | 3.0 |
| 1,800 | 35,100 | 78,750 | 36,000 | 3.0 |
| 2,000 | 39,000 | 87,500 | 42,000 | 3.5 |
| 2,500 | 48,750 | 109,375 | 54,000 | 4.5 |
| 3,000 | 58,500 | 131,250 | 60,000 | 5.0 |
| 3,500 | 68,250 | 153,125 | 60,000 | 5.0 |
| 4,000 | 78,000 | 175,000 | 60,000 | 5.0 |
Climate zone 7: very cold
Duluth, Grand Forks, International Falls. Cooling 16 to 20 BTU per sq ft, heating 45 to 55.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 8,750 | 24,375 | 18,000 | 1.5 |
| 600 | 10,500 | 29,250 | 18,000 | 1.5 |
| 800 | 14,000 | 39,000 | 18,000 | 1.5 |
| 1,000 | 17,500 | 48,750 | 18,000 | 1.5 |
| 1,200 | 21,000 | 58,500 | 24,000 | 2.0 |
| 1,500 | 26,250 | 73,125 | 30,000 | 2.5 |
| 1,600 | 28,000 | 78,000 | 30,000 | 2.5 |
| 1,800 | 31,500 | 87,750 | 36,000 | 3.0 |
| 2,000 | 35,000 | 97,500 | 36,000 | 3.0 |
| 2,500 | 43,750 | 121,875 | 48,000 | 4.0 |
| 3,000 | 52,500 | 146,250 | 54,000 | 4.5 |
| 3,500 | 61,250 | 170,625 | 60,000 | 5.0 |
| 4,000 | 70,000 | 195,000 | 60,000 | 5.0 |
Climate zone 8: subarctic
Fairbanks, Barrow. Cooling 15 to 18 BTU per sq ft, heating 50 to 60.
| Sq ft | Cooling BTU | Heating BTU | AC size | Tons |
|---|---|---|---|---|
| 500 | 8,063 | 26,875 | 18,000 | 1.5 |
| 600 | 9,675 | 32,250 | 18,000 | 1.5 |
| 800 | 12,900 | 43,000 | 18,000 | 1.5 |
| 1,000 | 16,125 | 53,750 | 18,000 | 1.5 |
| 1,200 | 19,350 | 64,500 | 24,000 | 2.0 |
| 1,500 | 24,188 | 80,625 | 30,000 | 2.5 |
| 1,600 | 25,800 | 86,000 | 30,000 | 2.5 |
| 1,800 | 29,025 | 96,750 | 30,000 | 2.5 |
| 2,000 | 32,250 | 107,500 | 36,000 | 3.0 |
| 2,500 | 40,313 | 134,375 | 42,000 | 3.5 |
| 3,000 | 48,375 | 161,250 | 54,000 | 4.5 |
| 3,500 | 56,438 | 188,125 | 60,000 | 5.0 |
| 4,000 | 64,500 | 215,000 | 60,000 | 5.0 |
Reading this chart honestly
Three things it cannot know, all of which move the answer:
- Your ceiling height. Every row assumes 8 ft. At 10 ft, add 25%.
- Your envelope. A 1960s house with single glazing sits at the top of its zone's band, a current-code build at the bottom. That spread is up to 14% either side of these numbers.
- Your actual design temperature. Climate zones are broad. A zone spans a real range of design conditions, and the edges of a zone behave more like their neighbours.