What Size Garage Will an 80,000 BTU Heater Heat?
An 80,000 BTU heater is sized for big spaces. Its 64,000 BTU/hr suits large or tall garages, uninsulated three-car garages and small workshops. For a typical 24 × 24 two-car garage it is far more than the model calls for.
How much garage it heats
Coverage depends on two things: how well the garage holds heat and how much warmer than outside you want it. The table uses an 8 ft ceiling. For a 10 ft ceiling, multiply the area by 0.8.
| Insulation | 30°F rise | 40°F rise | 50°F rise |
|---|---|---|---|
| Poor | 1,330 sq ft | 1,000 sq ft | 800 sq ft |
| Average | 2,010 sq ft | 1,500 sq ft | 1,200 sq ft |
| Good | 2,670 sq ft | 2,000 sq ft | 1,600 sq ft |
| Excellent | 3,330 sq ft | 2,500 sq ft | 2,000 sq ft |
Which garages it fits
Each garage below is at 20°F outside and 60°F inside, average insulation unless noted.
| Garage | Heat needed | This heater |
|---|---|---|
| 1-car, 12 × 20 ft | 10,000 BTU/hr | Oversized, about 6× the need |
| Compact 2-car, 20 × 20 ft | 17,000 BTU/hr | Oversized, about 4× the need |
| 2-car, 24 × 24 ft | 24,500 BTU/hr | Oversized, about 3× the need |
| 2-car, 24 × 24 ft, poor insulation | 37,000 BTU/hr | Yes, 73% to spare |
| 3-car, 32 × 24 ft | 32,500 BTU/hr | Yes, 97% to spare |
| Shop, 30 × 40 × 12 ft | 76,500 BTU/hr | No, 16% short |
Bigger or smaller?
Before buying this size for a house garage, check whether insulation or door seals would let a 50,000 or 60,000 BTU unit do the job. It is the right call for big detached garages, shops with roll-up doors and spaces with 12 ft ceilings. When the need passes its 64,000 BTU/hr of output, as a 30 × 40 shop with a 12 ft ceiling does, look at 100,000 BTU or two smaller units.
Gas use and running cost
Gas heaters are rated by input. At full fire this one burns about 0.80 therms of natural gas or 0.87 gallons of propane an hour. That costs about $1.18 or $2.23 an hour at 2025 average prices.
Over a month of 6-hour days with the heater running half the time, plan on about $107 on natural gas or $201 on propane. Put your own rate and hours into the cost to run a garage heater calculator.
Other gas heater sizes
- 30,000 BTU
- 50,000 BTU
- 60,000 BTU
- 80,000 BTU
80,000 BTU heater questions
How many square feet will an 80,000 BTU garage heater heat?
About 1,500 sq ft with an 8 ft ceiling, average insulation and a 40°F temperature rise. Good insulation stretches that to about 2,000 sq ft; a colder climate or a taller ceiling shrinks it.
Is an 80,000 BTU heater enough for a 2-car garage?
For a 24 × 24 × 8 ft garage at average insulation and a 40°F rise, yes. The garage needs about 24,500 BTU/hr and this heater delivers about 64,000, a 161% margin.
How much gas does an 80,000 BTU heater use?
At full fire it burns about 0.80 therms of natural gas an hour, or about 0.87 gallons of propane. Heating half the time over a 6-hour day, that is about $107 a month on gas or $201 on propane at 2025 average prices.
Sources
Checked October 1, 2026. Page dates are the publisher's own.
- EIA, British thermal units (Btu) (undated) · 1 therm = 100,000 Btu; propane 91,452 Btu per gallon
- NEC 424.4(B) branch-circuit sizing, quoted by Fast Trax (undated) · 125% of fixed space-heating load