Garage Heater BTU Chart
Find your garage, then read across to your winter. A 24 × 24 two-car garage needs about 24,500 BTU/hr at average insulation and a 40°F rise; a 1,000 sq ft garage needs about 42,500. Every number comes from the same engine as the calculator.
BTU by garage size and temperature rise
Average insulation, 8 ft ceiling. Use a higher column for a colder climate or a warmer target.
| Garage | 20°F rise | 30°F rise | 40°F rise | 50°F rise |
|---|---|---|---|---|
| 1-car12 × 20 × 8 ft | 5,000 | 7,500 | 10,000 | 13,000 |
| 2-car24 × 24 × 8 ft | 12,500 | 18,500 | 24,500 | 30,500 |
| 3-car32 × 24 × 8 ft | 16,500 | 24,500 | 32,500 | 41,000 |
BTU by garage size and insulation
Compare required heat output at the same temperature rise. The highlighted row matches your dimensions and door/window scenario. Other rows use their default enclosure. Values are BTU/hr; k means 1,000.
| Garage | poor | average | good | excellent |
|---|---|---|---|---|
| 1-car garage12 × 20 × 8 ft | 15,500 | 10,000 | 7,500 | 6,000 |
| Compact 2-car garage20 × 20 × 8 ft | 25,500 | 17,000 | 13,000 | 10,000 |
| 24 x 24 two-car garage24 × 24 × 8 ft | 37,000 | 24,500 | 18,500 | 14,500 |
| 3-car garage24 × 32 × 8 ft | 49,000 | 32,500 | 24,500 | 19,500 |
| 4-car example24 × 34 × 8 ft | 52,000 | 34,500 | 26,000 | 21,000 |
Poor15.5k
Avg10k
Good7.5k
Exc6k
Poor25.5k
Avg17k
Good13k
Exc10k
Poor37k
Avg24.5k
Good18.5k
Exc14.5k
Poor49k
Avg32.5k
Good24.5k
Exc19.5k
Poor52k
Avg34.5k
Good26k
Exc21k
Relative to average insulation, a poorly insulated garage needs about 50% more heat, a well insulated one about 25% less and a tightly sealed, fully insulated one about 40% less. The factors are on the methodology page.
Garage heater size by square feet
For a garage described by floor area, here is the heat needed at an 8 ft ceiling and a 40°F rise. A 10 ft ceiling adds 25%.
| Floor area | Poor | Average | Good | Excellent |
|---|---|---|---|---|
| 400 sq ft | 25,500 | 17,000 | 13,000 | 10,000 |
| 500 sq ft | 32,000 | 21,500 | 16,000 | 13,000 |
| 600 sq ft | 38,500 | 25,500 | 19,000 | 15,500 |
| 800 sq ft | 51,000 | 34,000 | 25,500 | 20,500 |
| 1,000 sq ft | 64,000 | 42,500 | 32,000 | 25,500 |
| 1,200 sq ft | 77,000 | 51,000 | 38,500 | 30,500 |
Why the chart is not a final answer
Charts cannot see your garage doors, windows, drafts, ceiling height or the coldest temperature you expect. Use them to get in the right range, then put your real numbers into the garage heater calculator before you buy.
Garage heater size chart questions
What size heater for a 1,000 square foot garage?
About 42,500 BTU/hr with an 8 ft ceiling, average insulation and a 40°F rise. Good insulation brings it to about 32,000 BTU/hr.
How do I read a garage heater size chart?
Pick the row closest to your garage, then the column for how much warmer than outside you want it. A 40°F rise means 20°F outside warmed to 60°F inside. Every value is heat output in BTU/hr, not a gas heater's input rating.
Why does my garage need more than the chart says?
Charts assume an 8 ft ceiling and a typical enclosure. Taller ceilings, big drafty doors, windows and colder design temperatures all add load. Enter your real numbers in the garage heater calculator to see the difference.