How Much Does It Cost to Heat a Garage?

Garage forums are full of people quoting monthly heating bills from $20 to $400, and both ends are right. The spread comes down to two things: whether the garage is insulated, and whether you keep it warm all week or heat it only while you're out there. Here's what each combination costs, using the same model as our garage heater calculator.

All figures are for an attached 2-car garage (24 × 24 ft, 9-ft ceiling) when it averages 30°F outside, at $1.70 per therm for natural gas, $2.50 a gallon for propane and 18¢ per kWh for electricity. "Heat pump" means a ductless mini-split.

Uninsulated 2-Car Garage: Monthly Cost

An open-stud garage with a bare ceiling and an uninsulated door loses about 630 BTU an hour for every degree it's warmer than outside. Holding 50°F all winter turns that into a bill most people won't accept: about $315 a month with propane. Heating it to 60°F only during an 8-hour weekend project costs a tenth of that.

Fully Insulated 2-Car Garage: Monthly Cost

Insulating the walls, ceiling and door cuts heat loss by about two-thirds. That's what makes keep-warm heating affordable: about $65 a month on natural gas or a mini-split to hold 50°F. If you only heat it a few hours a week, insulation saves $10–$30 a month and takes years to pay back, so it's worth doing mainly if you plan to keep the space warm.

What Size Heater a Garage Needs

Heater output needed to hold 60°F when it's 0°F outside, for attached garages with 9-ft ceilings:

For reference, a 1,500 W plug-in space heater makes about 5,100 BTU an hour, enough only for a small, insulated space. An uninsulated 2-car garage needs a 40,000–45,000 BTU propane or gas unit heater; an insulated one can get by on a 4–5 kW, 240-volt electric heater. Detached garages lose a little more because none of their walls touch the house.

Which Fuel Is Cheapest for a Garage

At these prices, natural gas and a ductless heat pump tie for the cheapest heat, propane costs about 60% more, and electric resistance heat about 2.5 times as much. But installation decides it for most people: a gas line or propane tank and a vent for a unit heater, a 240-volt circuit for an electric heater, or several thousand dollars for a mini-split, which also air-conditions the space in summer. For occasional use, the cheapest heater to install is often the right one, since the monthly bill is small either way.

Avoid running unvented propane or kerosene heaters for long periods. They dump combustion moisture and exhaust into the garage, which rusts tools and can raise carbon monoxide levels.

Frequently Asked Questions

How much does it cost to heat a 2 car garage?

For an attached 2-car garage at a 30°F outdoor average, heating to 60°F for 8 hours a week costs about $17 a month with natural gas, $28 with propane and $43 with an electric heater if it's uninsulated, and roughly a third of that if fully insulated. Keeping it at 50°F all the time costs about $195, $315 and $485 uninsulated, or $65, $105 and $160 insulated.

Is it worth heating a garage all the time?

Usually only to protect something, like water lines, paint and chemicals, or a workshop where finishes need to cure. Keeping a garage at 50°F all week costs about 11 times as much as heating it to 60°F for 8 hours a week. If you do keep it warm, 40°F costs about half as much as 50°F, and insulating the ceiling and door cuts the bill by about two-thirds.

What is the cheapest way to heat a garage?

Heat it only while you're using it. Per BTU, natural gas and a ductless mini-split heat pump are cheapest at typical prices, propane costs about 60% more and electric resistance about 2.5 times as much. For occasional use, the lowest-cost heater to install often makes the most sense because the monthly bill is small.

How many BTU to heat a 2 car garage?

To hold 60°F at 0°F outside, about 38,000 BTU an hour for an uninsulated attached 2-car garage, 32,000 with insulated walls only, and 13,000 when the walls, ceiling and door are insulated.