What Size Garage Will a 5,000 Watt Heater Heat?
Quick answer: A 5,000 watt garage heater makes about 17,060 BTU/hr, enough for about 400 sq ft of garage with an 8 ft ceiling, average insulation and a 40°F rise (20°F outside, 60°F inside).
A 5,000 W heater makes about 17,060 BTU/hr, enough in our model for a one-car garage or a compact, reasonably insulated two-car garage. At 240 V it points to a 30 A circuit in the usual 125% example.
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 | 360 sq ft | 270 sq ft | 210 sq ft |
| Average | 530 sq ft | 400 sq ft | 320 sq ft |
| Good | 710 sq ft | 530 sq ft | 430 sq ft |
| Excellent | 890 sq ft | 670 sq ft | 530 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 | Yes, 71% to spare |
| Compact 2-car, 20 × 20 ft | 17,000 BTU/hr | Yes, 0% to spare |
| 2-car, 24 × 24 ft | 24,500 BTU/hr | No, 30% short |
| 2-car, 24 × 24 ft, poor insulation | 37,000 BTU/hr | No, 54% short |
| 3-car, 32 × 24 ft | 32,500 BTU/hr | No, 48% short |
| Shop, 30 × 40 × 12 ft | 76,500 BTU/hr | No, 78% short |
A 5,000 watt heater falls 30% short of a 24 × 24 two-car garage at average insulation. The 2-car garage heater size guide compares 20 × 20 and 24 × 24 garages in BTU and watts, and the garage heater BTU chart lists every common size.
- 1-car, 12 × 20 ft, average insulation, 20°F outside: needs 10,000 BTU/hr (2,900 W). This heater covers it.
- 2-car, 24 × 24 ft, average insulation, 20°F outside: needs 24,500 BTU/hr (7,200 W). This heater is too small.
Bigger or smaller?
A 5,000 W heater is the sensible ceiling for a one-car garage and a stretch for a two-car. If your two-car garage is 24 × 24 or poorly sealed, the 7,500 W size is the safer buy. If it only needs to keep a workbench comfortable, a smaller 4,000 W unit on a 25 A circuit can be enough.
Circuit and breaker
At 240 V this heater draws about 20.8 A. The electrical code sizes fixed space-heating circuits at 125% of the load, about 26.0 A here, which points to a 30 A dedicated double-pole breaker in the usual example.
Treat that as a planning number. The heater's nameplate, its manual and a licensed electrician decide the breaker, the wire size and whether your panel has room.
Running cost
Electric resistance heat turns every watt into heat, so this heater uses 5 kWh for each hour at full power, about $0.86 at the 2025 U.S. average price. Over a month of 6-hour days heating half the time, that is about $78. Use the cost to run a garage heater calculator with your own rate.
Other electric heater sizes
- 5,000 watt
- 7,500 watt
- 10,000 watt
5,000 watt heater questions
How many square feet will a 5,000 watt garage heater heat?
About 400 sq ft with an 8 ft ceiling, average insulation and a 40°F temperature rise. Good insulation stretches that to about 530 sq ft; a colder climate or a taller ceiling shrinks it.
What size breaker does a 5,000 watt heater need?
At 240 V it draws about 20.8 A. Fixed electric heaters are sized at 125% of their load, about 26.0 A, which points to a 30 A dedicated circuit in the usual example. The heater's nameplate and your electrician decide the final breaker and wire.
How much does a 5,000 watt heater cost to run?
About $0.86 an hour at full power and about $78 a month if it heats half the time over a 6-hour day, at the 2025 U.S. average of 17.3¢/kWh.
Sources
Sources last checked November 7, 2026.
- U.S. Energy Information Administration, British thermal units (Btu) (accessed November 2026) · 1 kWh = 3,412 Btu; 1 therm = 100,000 Btu; propane 91,452 Btu per gallon
- U.S. Department of Energy, Energy Saver: Insulation (accessed November 2026) · why insulation level changes heat loss
- Mike Holt on NEC 424.3(B), fixed space-heating branch circuits (accessed November 2026) · branch circuit sized at 125% of the heater load