How many BTU to heat a two-car garage?
A 24×24 garage with 8 ft ceilings is 576 sq ft. Poorly insulated garages often need 30+ BTU/sq ft for heating — roughly 17,000–20,000 BTU. Uninsulated metal buildings need more.
Garage Heater BTU Calculator
Garages and workshops are poorly insulated with large overhead doors — we default to garage/workshop application type with lower insulation factors. Use heating BTU for winter comfort planning.
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Two-car garage example
A 24×24 garage with 8 ft walls is 576 sq ft. Poorly insulated shops often need 17,000–20,000+ BTU for comfortable winter work — insulate the door and ceiling first to cut required capacity.
See mini-split for garage workshop for year-round heat pump options vs dedicated garage heaters.
Propane, electric, and infrared
BTU output is comparable when rated equally. Ventilation and carbon monoxide safety matter for fuel-burning units — follow manufacturer clearance requirements.
Infrared heaters warm objects and people, not just air — useful for spot work zones. Forced-air units heat the whole volume faster but need more fuel when the door opens frequently.
Insulate before you upsize
A poorly sealed overhead door and uninsulated ceiling can double the heater BTU you need. Rigid foam on the door, weatherstripping, and attic/ceiling insulation often pay back faster than a larger burner.
Attached garages next to living space should keep combustion appliances code-compliant and sealed from living air. When in doubt, use electric or a heat pump and follow local clearances.
Related winter sizing tools
Planning whole-home furnace capacity? Use the furnace BTU calculator. Comparing cold-climate heat pumps vs backup heat? Open the heat pump cold climate calculator.
Related guides
Frequently asked questions
Does opening the garage door affect sizing?
Yes. Frequent door cycles add heat loss. Size toward the upper end or add insulation first — ceiling and garage door kits dramatically cut required BTU.
Propane vs electric garage heater BTU?
BTU output is comparable when rated equally. Propane units often deliver higher peak BTU for large shops; electric is simpler for attached garages with existing service.
Related calculators
HVAC Calculators · https://hvaccalculators.net/garage-heater-btu-calculator/