We recommend a ceiling-mounted, gas-fired, forced-air unit heater. Some installers recommend infrared heaters because they heat objects instead of air. You’ll be warmed and so will the floor (if it’s free of vehicles). But you won’t be happy with the cold tools inside your tool chest. Infrared heaters are no more energy efficient than forced-air heaters, and they cost about twice as much.
The least expensive alternative is a portable kerosene or propane heater. But they’re a poor choice. They require ventilation (think “open door”) and pump gallons of water vapor into your garage. That means working with a constant cold draft and putting up with smelly exhaust and burning eyes. Then there’s the issue of rust on your tools from all that humidity. Kerosene and propane heaters just aren’t a good solution if you work in the garage regularly. So bite the bullet and buy a ceiling-mounted, forced-air unit heater that’s rated for residential use (building inspectors won’t OK an industrial unit in a residential garage). Plan to spend $500 to $650, plus the cost of professional installation. Advanced DIYers can install a unit heater, which involves gas lines, venting and electrical work. But don’t skip the permits and inspections. An improper installation can kill you. Check with the inspector to see if it’s even legal in your area to perform your own gas hookups.
If you’ll be working on wood projects or using spray finishes, choose a heater with a separate combustion chamber. They burn fresh outside air instead of the dust or paint-laden air inside a garage. There’s a slight fire danger using a conventional heater, and the dust and paint particles will cause burner problems that require service calls.
Some unit heaters are more compact than others and can be mounted within 1 in. of the ceiling. So review the dimensions of the heater and calculate the installed height to ensure proper headroom.
To help size the heater and estimate monthly energy costs, consult manufacturers and dealers. Most residential garages require heaters with a capacity of 30,000 or 45,000 Btu. Your heater size depends on the garage’s square footage, ceiling height and insulation, so don’t guess. And don’t oversize your heater—especially if you intend to leave it on (even at a reduced temperature) all winter. An oversize unit heater cycles too often and wastes energy.
If you have an attached garage, mount the thermostat on the common wall between the garage and the house and away from the heated airflow. In a detached garage, mount it on the wall below the heater.