How to Heat a Garage or Workshop Through Winter

A cold garage is a wasted room. It is where projects stall, batteries drain, paint freezes and cars start reluctantly, and yet most homeowners treat winter heat out there as impossible or ruinously expensive. It is neither. Learning how to heat a garage in winter is mostly a matter of order: seal and insulate the shell first, calculate how much heat the space needs, then choose a heater whose fuel matches the wiring and venting you already have. Skip the first two steps and you will buy a heater that runs constantly and never quite wins.

What You Will Need Before You Start

Gather the following before you spend a dollar on heating equipment. Most of this list is measurement and sealing gear rather than anything exotic.

• Tape measure and calculator for square footage and ceiling height.
• Infrared thermometer or a simple stick thermometer to find cold spots and confirm results.
• Weatherstripping and a garage door bottom seal — the single highest-value purchase in this project.
• Expanding foam and exterior-grade caulk for rim joists, sill plates and wall penetrations.
• Fiberglass batts, mineral wool or rigid foam board sized to your stud and rafter depth.
• Utility knife, staple gun, stud finder, safety glasses, gloves and a dust mask.
• A voltage tester and knowledge of your panel’s spare capacity if you are considering electric heat.
• A carbon monoxide alarm — non-negotiable if you will burn any fuel in the space.

Step by Step: Heating a Garage for Winter

1. Measure the space and set a realistic target. Multiply length by width for square footage, and note the ceiling height, since a garage with a vaulted or truss-open ceiling has far more air volume than the floor area suggests. Decide what you actually need: roughly 50 degrees Fahrenheit is enough to protect tools, fluids and paint and to keep a car easy to start, while 60 to 65 degrees is what you want for comfortable hands-on work. Heating to living-room temperature in an uninsulated garage is the most common way people convince themselves the project failed.
2. Seal every air leak you can find. Air leakage, not conduction, is what kills garage heat. Close the door and look for daylight around the perimeter. Replace the rubber bottom seal, renew the side and top weatherstripping, and caulk where the wall framing meets the slab. Foam around penetrations, hose bibs and the rim joist. This stage alone can cut your heating load dramatically.
3. Insulate the walls and ceiling. Fill the wall cavities with batts sized to the stud depth, then insulate the ceiling or roof deck, since heat rises and an uninsulated lid undoes everything below it. If the garage is attached, the shared wall to the house matters most. Rigid foam board is the practical choice on masonry walls that have no stud cavity.
4. Insulate the garage door itself. A bare steel door is effectively a large window in your thermal envelope. Panel insulation kits are inexpensive and fit most sectional doors in an afternoon.
5. Calculate the heater size you need. A quick and reliable rule for a sealed, insulated garage is 30 to 45 BTU per square foot in a cold climate, or roughly 10 watts per square foot for electric heat. A 400 square foot single-car garage therefore lands near 15,000 BTU or about 4,000 watts. A 600 square foot two-car garage lands near 25,000 BTU. Add 25 percent if the ceiling is high or insulation is thin. Undersizing means the unit never catches up; heavy oversizing means short, inefficient cycles.
6. Choose a fuel and heater type that matches your building. This is the fork in the road, and it depends far more on your electrical panel and venting options than on brand preference. Compare the options in the next section before buying.
7. Mount and position the heater properly. Ceiling or high-wall mounting is standard for forced-air units, angled to sweep warm air across the working area rather than straight down at a workbench. Keep the clearance to combustibles listed in the manual, and never point a heater at stored fuel, solvents or sawdust. Because flammable vapors collect at floor level, mount any fuel-burning heater high.
8. Add controls so the heat is not always on. A thermostat is what turns a heater from an expensive novelty into a practical system. Set a low background temperature for freeze protection and a higher setpoint for the hours you plan to work. Line-voltage thermostats suit baseboard and many electric unit heaters, while low-voltage models pair with gas unit heaters and mini-splits.
9. Manage moisture as well as temperature. Warm air holds more water. A car dripping snowmelt on a warm slab releases moisture that condenses on cold tools and encourages rust. Allow a little controlled ventilation and consider a dehumidifier in damp attached spaces. The same logic that applies to crawl space dehumidifiers in an unconditioned basement applies to a heated garage that keeps sweating.
10. Test, measure and tune for a week. Place a thermometer at working height, not at the ceiling, and log how long the space takes to reach setpoint from cold. If it never arrives, you have either an undersized heater or a leak you missed. If it overshoots and swings, move the thermostat away from direct heater airflow or drafty doors.

Choosing the Right Heater Type

Electric unit heaters are the simplest and safest option because there is nothing to vent and no combustion byproduct. The catch is capacity: anything meaningful for a two-car garage needs a 240-volt circuit and often 20 to 30 amps, so check that your panel has spare breaker space before you commit. Running cost is higher per BTU than gas in most regions, but installation is far cheaper.

Natural gas or propane unit heaters deliver the most heat for the lowest running cost and shrug off very cold weather. They must be vented to the outdoors, which means cutting the wall or roof and following the manufacturer’s flue requirements exactly. Budget for a gas line and a professional connection if you are not licensed for that work.

Ductless mini-split heat pumps are the efficiency champion and the only option that also cools the garage in summer. They cost the most up front, though cold-climate models now perform well below freezing.

Infrared radiant heaters warm objects and people rather than the air, which suits a poorly insulated garage or one with a door that opens constantly. You feel warm instantly in the beam, but the space itself never really heats.

Controlling the Heat Efficiently

Whatever heater you install, the control strategy determines the bill. A garage does not need to be warm at 3 a.m. on a Tuesday, so a schedule that holds 45 to 50 degrees overnight and climbs to your working temperature an hour before you head out captures most of the comfort for a fraction of the energy. If you are picking a controller, our roundup of the best thermostats covers the full range of options, while the best programmable thermostats are the natural fit for a space used on a predictable schedule.

Not every garage needs connectivity. Detached buildings often have weak Wi-Fi and no C-wire, and a rugged dial or simple digital unit is more reliable in a dusty, cold, unattended space. The best non-smart thermostats handle exactly this job without an app or a network dependency. Whichever route you take, build a sensible setback pattern first — our walkthrough on how to choose a thermostat schedule explains how deep a setback can go before recovery costs more than it saves.

Safety Rules You Should Not Bend

Garages store the things that make heating risky: gasoline, propane cylinders, paint thinner, sawdust and running engines. Install a carbon monoxide alarm before you install any combustion heater, and test it monthly. Never use an unvented kerosene or propane salamander heater in a closed garage for extended periods — those units dump both moisture and combustion gases straight into the room and are designed for ventilated construction sites.

Keep a three-foot clearance around any heater, store flammable liquids in sealed containers away from the unit, and never run an engine in a heated, sealed garage. Electric heaters should be hardwired or on a dedicated circuit; extension cords are a frequent cause of garage fires.

Troubleshooting a Garage That Will Not Warm Up

If the heater runs continuously without hitting setpoint, work through the causes in order. First suspect air leakage — a poorly sealed door can exchange the whole volume of air several times an hour. Second, check ceiling insulation, since warm air stratifies at the roof and escapes there. Third, verify the heater delivers rated output: an electric unit wired to the wrong voltage produces roughly a quarter of its rating.

If the temperature swings wildly instead, the thermostat is probably in the heater’s airstream or beside the door. Relocate it to an interior wall at chest height.

Common Mistakes to Avoid

• Buying the heater first. Sealing and insulating changes the size you need, sometimes by half.
• Ignoring the garage door. It is often a third of the exterior surface and usually the worst-performing part of it.
• Sizing by guesswork. Use BTU per square foot and adjust for ceiling height rather than picking the biggest unit on the shelf.
• Running a portable unvented heater all day. Fine for a quick task, hazardous as a heating strategy.
• Leaving the heater on a manual switch. Without a thermostat you either waste energy or forget it entirely.
• Forgetting humidity. Warm, damp garage air rusts tools faster than cold, dry air ever did.

Frequently Asked Questions

How many BTU do I need to heat a two-car garage?

For a sealed and insulated 600 square foot garage in a cold climate, plan on roughly 25,000 BTU, or about 6,000 watts of electric heat. Add 25 percent for a high ceiling, minimal insulation or frequent door openings.

Is it cheaper to heat a garage with gas or electricity?

Gas almost always costs less to run where natural gas is available, but it requires venting and a gas line, so installation costs more. Electric heat wins on simplicity and up-front cost, and a cold-climate mini-split can rival gas on running cost thanks to its efficiency.

Can I heat a garage without insulating it first?

You can, but the heat escapes almost as fast as you add it, so the heater runs constantly and the bill climbs. Radiant heaters are the practical exception because they warm you directly rather than trying to warm the room.

What temperature should I keep an unused garage in winter?

Around 45 to 50 degrees Fahrenheit protects stored liquids, batteries and plumbing without meaningful expense. Raise it only for the hours you plan to work in the space.

Final Thoughts

Heating a garage well in 2026 is far less about the equipment than the sequence. Seal the leaks, insulate the shell and the door, then size a heater to the space you have actually created rather than the drafty box you started with. Match the fuel to your panel and venting options, add a thermostat with a sensible setback schedule, and keep a carbon monoxide alarm in place. Done in that order, a winter garage becomes the extra room you always intended it to be.