How the math works
The calculator starts with heater output, not a sales label. Electric resistance heat uses output BTU/hr divided by 3,412 to find kWh, then multiplies by your electric rate and duty cycle. Natural gas and propane first divide delivered output by 80% efficiency to find fuel input, then divide by BTU per therm or gallon and multiply by the fuel rate. Every result then multiplies by your daily hours, days per week, and 4.345 weeks per month.
Duty cycle is the share of each hour that the heater actually runs. It matters because a thermostat turns the heater on and off after the garage reaches temperature. The result card therefore shows an average cost per hour of garage use, not an uninterrupted hour of element or burner runtime.
A default worked example
A 24 x 24 ft garage in the sizing calculator needs about 24,500 BTU/hr with average insulation and a 40 F temperature rise. At 19 cents per kWh, that electric load costs about $1.36 per hour if it ran continuously. At the typical 65% duty cycle, it costs about $0.89 per hour of garage use. Five hours a day, five days a week works out to about $96 per month before changing the season length.
Delivered heat cost by fuel
Comparing fuel bills is clearer when every option is measured per million delivered BTU. At the default national-average rates, natural gas is usually lowest, then propane, then electric resistance heat. Those are comparison points, not promises. Your local utility bill, propane delivery price, and heater efficiency can move the order.
| Fuel | Default rate | Cost per million delivered BTU |
|---|---|---|
| Natural gas | $1.68/therm | $21.00 |
| Propane | $2.67/gal | $36.49 |
| Electric resistance | $0.19/kWh | $55.69 |
Three ways to cut running cost
Start with insulation and door sealing. A tight, insulated door and fewer air leaks reduce the heat your garage loses before you spend money on a larger heater. The methodology explains why insulation changes the sizing estimate so much.
Next, lower the target temperature when you are not actively working. A few degrees less temperature rise reduces the heat loss that drives the estimate. Use the garage heater calculator to compare the difference for your dimensions and weather.
Finally, heat the work area instead of the whole space when that matches how you use the garage. A focused electric or infrared setup can cost less than keeping every bay warm for a short project.
Questions
Garage heater cost questions
How much does it cost to run a garage heater per hour?
With the default inputs, a 24,500 BTU/hr electric load costs about $0.89 per hour of garage use at 19 cents per kWh and a 65% duty cycle. Local energy rates change the result.
How much does it cost to run a 1,500 watt garage heater?
1.5 kW x $0.19 is about $0.29 per hour while the heater is actually running. With thermostat cycling, the average cost per hour of garage use is lower.
Is propane or electric cheaper for heating a garage?
At 2026 national average prices, delivered heat costs roughly $21 per million BTU for natural gas, $37 for propane, and $56 for electric resistance. Local rates decide, so run the calculator with your own numbers.
Why does the calculator multiply by a duty cycle?
Thermostat cycling means a heater draws rated power only part of each hour. A 50 to 80 percent duty cycle covers most garages, and rated-power-times-hours would overestimate by a third or more.