Install a Garage Heater

Turn a cold, damp, unpleasant workspace into a year-round hangout.

As winter approaches, that beloved garage you spend so much time in can morph into a cold, damp, unpleasant workspace. So why not take steps now to warm it up later? A natural-gas or propane heater is safer, cleaner and more convenient than burning wood — just fl ip a switch and the heat is on — and if you install a thermostat and insulation, you can keep your garage a consistent temperature no matter how cold it is outside. (Note: Before you begin, check with your local building authority for applicable codes and permits.)

Determine the right size and location of your heater
Before you purchase a natural-gas or propane heater, be sure to check the unit’s specifications for Btu output and square footage. We installed a Mr. Heater Big Maxx, which is available in two sizes: 45,000 and 75,000 Btu. The smaller unit works for spaces up to 700 sq. ft. and the larger unit works for areas up to 1,000 sq. ft.

The heater we used is equipped with a blower, so we installed it near the garage ceiling for optimal air circulation — an upper corner opposite the main door is best.

Venting is another factor in choosing a location. Be sure to read the manufacturer’s specifications before installation. (You can vent the Big Maxx Heater through the roof or through the wall. If you vent through the wall, the horizontal vent must be between 3 and 5 ft. long.)

Run the gas line and install the disconnect switch
Unless you are experienced in gas and electrical installations, leave this step to the professionals. The gas and electrical connections will need to be installed according to the manufacturer’s instructions and code. For the Big Maxx Heater, the manufacturer recommends installing a disconnect switch (similar to a light switch) in a wall near the heater. The typical cost of a gas-line installation is $400, and wiring an additional electrical switch costs approximately $300.


Hire a plumber or an HVAC professional to run the gas line.

Provide adequate support for the heater
We attached the unit to a piece of 3/4-in. plywood (see photo, below). This allowed for continuous support when installing the heater across ceiling joists.


Fasten the heater to 3/4-in. plywood; then attach the plywood to the ceiling joists.

Cut a hole for the vent
First, determine the size and height of hole you will need to terminate the heater venting. Horizontal venting must slope upward 1/4 in. per 1 ft. of run. Measure the distance between the top of the heater and the center of the vent output; then measure the distance between the vent output and the wall. Subtract 1/4 in. per foot of run between the vent output and the wall. Use this result to mark the center of the vent hole. If the wall is covered with drywall, locate the studs with a stud finder so you can cut the opening in a stud cavity.


Cut a vent hole and install the vent-pipe thimble.

Once you determine the hole’s location, use a compass to mark it on the inside of the exterior wall. Make sure the circle is about 1/4 in. larger than the diameter of the vent-pipe thimble. Drill a pilot hole through to the exterior side of the wall; then use the compass to make a circle on that side. Cut the interior and exterior wall with a hole saw or reciprocating saw and install the vent-pipe thimble (photo, above).

Attach the heater’s plywood support to the ceiling joists and install the vent pipe. Then enlist the help of a plumber or HVAC professional once again to connect the gas line to the heater.


Insulating your garage
Adding insulation to your heated garage will help you conserve energy and save money. To make the best decisions about your garage’s insulation, it’s essential to understand two concepts: heat transfer and R-value.

Heat transfer explains how heat moves from the warm side of the insulation to the cold side in three ways: radiation, conduction and convection. Radiation, such as the warmth that is created by sunlight, is the transfer of heat from one object to another through airspace. Conduction, on the other hand, is the transfer of heat between two objects that are actually touching. For example, if it weren’t for the air that’s trapped within their structure, insulation materials such as mineral wool or fiberglass would transfer heat from the outside wall to the inside wall simply because the material touches both surfaces. But while trapped stationary air within insulation helps its performance, moving air — convection — hinders it. Convection can occur when cold air displaces hot air, causing it to rise and create what’s known as a convective loop, which can transfer heat out of the home in winter and into it during the summer.

To combat heat transfer, it’s necessary to increase a wall surface’s R-value — the higher the R-value, the greater the insulating power. Manufacturers of insulation products print the R-values of their products either on the packaging materials or on labels. In most cases, R-values are also printed on the facings of fiberglass batts and rolls.

Although some manufacturers promote the “per inch” R-value of their products, the overall R-value when the product is installed is what counts. Common R-values for home- and garage-insulation products range from R-8 to R-38, depending on the materials.


Wire the thermostat to the heater
Attach the thermostat wires to the heater according to the manufacturer’s instructions. Place the thermostat in an area that is not directly in the path of the heater fan. A side-wall location about 4 to 5 ft. from the floor is the best choice.

Once the thermostat is wired and the gas and electrical connections are tested and secure, your heater is ready to be switched on so it can warm up your workspace.


Bonus Video: