What Size Garage Will a 30,000 BTU Heater Heat?
In our sizing table, 30,000 BTU is the smallest gas input class. At 80% efficiency it puts out about 24,000 BTU/hr, just short of what a 24 × 24 garage needs at average insulation and a 40°F rise. In the model it covers one-car garages, compact two-car garages and well-insulated spaces.
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 | 500 sq ft | 380 sq ft | 300 sq ft |
| Average | 750 sq ft | 560 sq ft | 450 sq ft |
| Good | 1,000 sq ft | 750 sq ft | 600 sq ft |
| Excellent | 1,250 sq ft | 940 sq ft | 750 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 2× the need |
| Compact 2-car, 20 × 20 ft | 17,000 BTU/hr | Yes, 41% to spare |
| 2-car, 24 × 24 ft | 24,500 BTU/hr | No, 2% short |
| 2-car, 24 × 24 ft, poor insulation | 37,000 BTU/hr | No, 35% short |
| 3-car, 32 × 24 ft | 32,500 BTU/hr | No, 26% short |
| Shop, 30 × 40 × 12 ft | 76,500 BTU/hr | No, 69% short |
Bigger or smaller?
If your garage is a full 24 × 24 or you live where winters regularly drop below 20°F, skip this size and look at 45,000 or 50,000 BTU. The 30,000 BTU class fits compact garages, insulated spaces and mild climates, where a bigger burner would only short-cycle.
Gas use and running cost
Gas heaters are rated by input. At full fire this one burns about 0.30 therms of natural gas or 0.33 gallons of propane an hour. That costs about $0.44 or $0.84 an hour at 2025 average prices.
Over a month of 6-hour days with the heater running half the time, plan on about $40 on natural gas or $75 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
30,000 BTU heater questions
How many square feet will a 30,000 BTU garage heater heat?
About 560 sq ft with an 8 ft ceiling, average insulation and a 40°F temperature rise. Good insulation stretches that to about 750 sq ft; a colder climate or a taller ceiling shrinks it.
Is a 30,000 BTU heater enough for a 2-car garage?
Not for a 24 × 24 × 8 ft garage at average insulation and a 40°F rise. That garage needs about 24,500 BTU/hr and this heater delivers about 24,000. It can work for a compact or well-insulated two-car garage.
How much gas does a 30,000 BTU heater use?
At full fire it burns about 0.30 therms of natural gas an hour, or about 0.33 gallons of propane. Heating half the time over a 6-hour day, that is about $40 a month on gas or $75 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