Garage heating planner
Garage Heater Calculator
Find the right heater size for your garage. Estimate BTU/hr, electric watts, and the next standard heater size from your dimensions and winter conditions.
This is a planning estimate, not a professional heat-loss calculation. Air leakage, windows, roof construction, local wind, and heater placement can change the capacity you need.
Method
How this garage heater calculator works
This planner estimates heat output from garage volume, expected winter temperature, and how well the space is insulated. It is designed to narrow a shopping shortlist, not replace a room-by-room heat-loss calculation.
Compare units
BTU/hr vs. electric watts
Electric heaters are usually listed in watts; gas and propane equipment is usually listed in BTU/hr. The calculator shows both values so you can compare equipment without converting figures by hand. Gas and propane guidance assumes 80% efficiency when translating required heat output to listed input capacity.
Common sizes
Choose a starting point
FAQ
Garage heater sizing questions
How many BTU do I need for a two-car garage?
It depends on the garage dimensions, insulation, and your coldest winter temperature. A 24 x 24 x 8 ft garage at average insulation needs about 24,500 BTU/hr for a 40 F temperature rise; a compact 20 x 20 needs about 17,000 BTU/hr under the same conditions.
What is the electric equivalent of 25,000 BTU/hr?
About 7,300 watts (1 watt equals 3.412 BTU/hr). Confirm the electrical circuit can support the heater before buying, especially when the estimate approaches 10,000 watts.
Can I run a garage heater on a regular 120V outlet?
Only up to 1,500 watts, which is about 5,100 BTU/hr. That suits a small, well-insulated garage in a mild climate or spot heating at a workbench. Anything larger needs a dedicated 240V circuit installed by an electrician.
Do gas garage heaters list input or output BTU?
Gas and propane unit heaters are listed by INPUT BTU. At roughly 80% efficiency, a 60,000 BTU input unit delivers about 48,000 BTU/hr of heat. Compare your required output against the unit's output, or divide input by 1.25 as a quick check.
Should I size up a garage heater?
Yes, to the next standard capacity above the estimate, never below it. Stop there: a unit rated at more than about twice the requirement costs more, cycles on and off, and heats unevenly.
What if my garage is uninsulated?
Choose "Poor" insulation and the calculator plans for the extra loss, roughly 50% more capacity than an average garage. Before buying that much heater, price insulating the garage door and walls: it often costs less than the capacity jump and saves fuel every winter.