Garage Heater Wattage — What Size Do You Need?
Use this guide to find the right heater size for your garage. Avoid underpowered or oversized units.
A 1-car garage needs 3,000–5,000 watts (10,000–17,000 BTU).
A 2-car garage needs 5,000–7,500 watts (17,000–25,000 BTU).
Add 25% for poor insulation or climates below 20°F.
Garage Heater Size Guide (US 2026)
| Garage Size | Sq Ft | Watts Needed | BTU Needed |
|---|---|---|---|
| 1-Car garage | 250 | 3,000–5,000W | 10,000–17,000 |
| 2-Car garage | 500 | 5,000–7,500W | 17,000–25,000 |
| 3-Car garage | 750 | 7,500–10,000W | 25,000–34,000 |
| Large workshop | 1,000 | 10,000–14,000W | 34,000–48,000 |
Add 25% for poorly insulated garages or cold US climates with average winter temps below 20°F.
Calculate the Right Heater Size for Your Garage
How to Choose the Right Garage Heater Size
Use 10 watts per square foot as a starting point for a well-insulated garage. A 500 sq ft 2-car garage needs roughly 5,000 watts minimum. Add 25% for poor insulation or climates regularly below 20°F. Use the calculator above for a precise recommendation.
BTU and wattage measure the same output differently. One watt equals 3.41 BTU/hr. A 5,000W heater delivers roughly 17,000 BTU/hr — enough for a standard 2-car garage in most US climates above freezing. See running cost breakdowns for electric garage heaters and propane garage heaters.
Always check your garage electrical panel before buying an electric heater. Units above 4,000 watts require a 240V dedicated circuit. Propane and gas heaters avoid this limitation entirely for larger garages and workshops. Compare all types with the garage heater cost calculator.