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Garage Heating, Cooling and Insulation: Comfort All Year

Insulate and seal your garage, size a heater from your own walls and door, and choose cooling, ventilation and dehumidification that fit.

A garage that is freezing in winter and stifling in summer is hard to use for anything but parking. The order of operations matters: seal and insulate first, then heat, cool, ventilate and control humidity. This hub explains each step and how to size equipment for your garage instead of guessing.

Seal and insulate first

ENERGY STAR describes R-value as a measure of insulation’s ability to resist heat traveling through it; the higher the R-value, the better the thermal performance. In a garage, the biggest weak points are usually the garage door, the gaps around it and an uninsulated ceiling. Simple fixes such as weather stripping and caulking come first. See the garage insulation guide and how to insulate a garage door.

Heating your garage

Electric heaters are simple to install on a dedicated circuit and produce no combustion gases. Propane and natural gas heaters deliver more heat for their size but must be rated for garage use and vented as their manuals require. Size the heater from your garage’s heat loss with the Garage Heater Size Calculator.

Heater safety

The U.S. Fire Administration advises keeping anything that can burn at least 3 feet from all heat sources and turning space heaters off when leaving the room or going to bed. It reports that home portable heater fires were only 3 percent of home heating fires annually for 2017 to 2019 but accounted for 41 percent of fatal heating fires in homes. In a garage, keep heaters well away from fuel, solvents and sawdust.

Cooling and ventilation

An exhaust fan with a source of makeup air removes trapped heat and fumes; size it with the Garage Ventilation Calculator. For real cooling, ductless mini splits heat and cool from one system, and ENERGY STAR says certified mini splits use up to 60 percent less energy than standard home electric radiators. ENERGY STAR also notes that an oversized air conditioner costs more to buy, wastes energy and does not cool better. See the garage air conditioner guide.

Humidity and mold

The EPA advises keeping indoor humidity below 60 percent, ideally between 30 and 50 percent. Damp garages rust tools and grow mold. ENERGY STAR says a certified dehumidifier removes the same amount of moisture as a similar conventional unit using 20 percent less energy, and its sizing chart starts at 20 to 30 pints per day for a small to medium space that feels slightly to moderately damp. See the garage dehumidifier guide.

Carbon monoxide

The EPA warns not to idle a car inside a garage. Deadly levels of carbon monoxide can build up quickly and linger for hours. Never run vehicles, generators or unvented fuel-burning equipment with the garage door closed, and keep the door between an attached garage and the house closed.

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Frequently asked questions

What is the best way to heat a garage?

Insulate and seal first, then choose a heater sized for your garage’s heat loss. Electric heaters are simplest to install; gas heaters must be rated for garages and vented as required.


How do I keep my garage cool in summer?

Seal gaps, insulate the door and ceiling, ventilate with an exhaust fan and makeup air, and use a mini split or room air conditioner sized for the space for real cooling.


Do I need a dehumidifier in my garage?

If the garage feels damp, tools rust or you see mold, a dehumidifier helps. The EPA advises keeping indoor humidity below 60 percent, ideally 30 to 50 percent.


Is it safe to use a propane heater in a garage?

Only a heater rated for garage use, operated with the ventilation its manual requires, with a carbon monoxide alarm and well away from fuel and solvents.