Rule-of-thumb BTU per sq ft by climate zone
These BTU-per-square-foot bands are rule-of-thumb estimates by IECC climate zone, not a load calculation. They give a first-pass size; a professional Manual J accounts for insulation, windows, orientation and infiltration. Use the AC-size and furnace-size tools to apply them with adjustments.
Every figure below is capacity — BTU per hour per square foot — even where a column reads BTU/sq ft for short. If that distinction is new to you, BTU explained covers BTU versus BTU/h before you size anything from these bands.
Cooling — rule-of-thumb BTU/sq ft
| Climate | BTU/sq ft | 1,500 sq ft ≈ |
|---|---|---|
| Cool / northern | 20 | 30,000 BTU (2.5 tons) |
| Moderate / mixed | 25 | 37,500 BTU (3.1 tons) |
| Warm / southern | 30 | 45,000 BTU (3.8 tons) |
| Hot / desert | 35 | 52,500 BTU (4.4 tons) |
Heating — rule-of-thumb BTU/sq ft
| Climate | BTU/sq ft | 1,500 sq ft ≈ |
|---|---|---|
| Mild winter | 30 | 45,000 BTU output |
| Moderate | 40 | 60,000 BTU output |
| Cold | 50 | 75,000 BTU output |
| Very cold | 60 | 90,000 BTU output |
Rule-of-thumb estimates by IECC climate zone — a starting point, not a Manual J load calculation.
Heating bands for Canada
IECC climate zones stop at the border. These rows map each province and territory onto the same four heating bands using heating degree-days below 18 °C, so a Canadian reader can pick a band from the heating table above. Each page works the band through to a BTU/h figure for its major centres.
| Province / territory | Reference city | Heating degree-days | Band |
|---|---|---|---|
| British Columbia | Vancouver | 2,781 | Mild winter (~30 BTU/sq ft) |
| Alberta | Calgary | 4,994 | Cold (~50 BTU/sq ft) |
| Saskatchewan | Regina | 5,626 | Cold (~50 BTU/sq ft) |
| Manitoba | Winnipeg | 5,672 | Cold (~50 BTU/sq ft) |
| Ontario | Toronto | 3,434 | Moderate (~40 BTU/sq ft) |
| Quebec | Montreal | 4,281 | Moderate (~40 BTU/sq ft) |
| New Brunswick | Fredericton | 4,601 | Cold (~50 BTU/sq ft) |
| Nova Scotia | Halifax | 4,189 | Moderate (~40 BTU/sq ft) |
| Prince Edward Island | Charlottetown | 4,517 | Cold (~50 BTU/sq ft) |
| Newfoundland and Labrador | St. John's | 4,690 | Cold (~50 BTU/sq ft) |
| Yukon | Whitehorse | 6,491 | Very cold (~60 BTU/sq ft) |
| Northwest Territories | Yellowknife | 8,009 | Very cold (~60 BTU/sq ft) |
| Nunavut | Iqaluit | 9,642 | Very cold (~60 BTU/sq ft) |
Heating degree-days from the Environment and Climate Change Canada Canadian Climate Normals 1991–2020. Several provinces span more than one band — the reference city is the largest centre, not a provincial average. See HVAC sizing in Canada.