How to Find the Right Size Garage Heater

The best way to save money on a NewAir garage heater is to buy one the right size. If your heater’s too large, it will run up your power bills trying to heat a space beyond its capacity. If it’s too big, you’ll be paying money for extra heating capacity you’re never going to use. Fortunately, sizing a space heater is relatively easy. All it requires is a few simple measurements and a bit of math.

Watts and BTUs           

There are two types of garage heaters, gas and electric, and they’re each measured differently. Gas heaters rated according to BTUs (British Thermal Units). A BTU is the amount of energy required to heat one cubic foot of water by one degree.

Electric heaters are rated according to watts. Watts measure the rate of energy transfer and are defined as one joule per second. One watt is approximately 3.41 BTU. To convert between the two, follow these simple equations:

Watts * 3.41 = BTU

BTU/3.41 = Watts

NewAir garage heaters are all electric heaters.

Garage Heater Size

The quickest way to estimate the size of your garage heater is to follow the basic rule of 10 watts per square foot of space. If your garage is 24 ft. x 24 ft., for example, it has an area of 528 square feet (24 * 24 = 528) and would require a 5280 watt garage heater (528 * 10 = 5280).

How to Find the Right Size Garage Heater
NewAir G73 Hardwired Electric Garage Heater

For a more precise measurement, you need to take into account the volume of your garage, the degree of insulation in your garage, and your desired temperature rise.

Temperature Rise

Temperature rise refers to the difference between the temperature outside and your desired temperature inside. If the average temperature outside your garage is 50°F, and you wanted to heat your garage to 70°F, then the temperature rise would be 20°F (70°-50° = 20°).


To measure the degree of insulation in your garage, you need to check its R-value. R-value is a measure of thermal resistance. It tells you how well a material traps and retains heat. Materials with high R-value are good insulators. Materials with low R-value are not.

How much insulation you need depends on where you live. Recommended R-value for buildings in cold climates is high (18-27), and low for buildings in warm climates (13-15). Find the recommend R-value for your area by clicking here and rate your insulation based on how closely it matches your recommended levels.

Degree of Insulation











Finally, calculate the volume of your garage by multiplying its length, width, and height. For example, a 24 ft. x 24 ft. garage with an eight-foot ceiling has a volume of 4608 ft.3 (24 * 24 * 8 = 4608)

Final Formula

Once you have all the data assembled, multiply them together and divide by 1.6 to find the number of BTUs required to heat your garage.

(Insulation * Volume * Temp. Rise)/1.6 = BTU

For example, if your garage was 4608 ft.3 in volume, your temperature rise was 20°F, and your insulation rating was one, it would be:

(1 * 4608 * 20)/1.6 = 57,600 BTU

If you wanted to convert that to watts, you’d divide by 3.41.

52,800/3.41 = 16,891 Watts

That’s how to find the right size NewAir garage heater. If you have any questions, leave them in the comments!

How to Find the Right Size Garage Heater


6 thoughts on “How to Find the Right Size Garage Heater

  1. according to your sizing formula, i need a heater with a capacity of 21774 watts. can you provide an electric 240 volt system that will work for me?

  2. Hello Gary,
    We currently only carry one garage heater that is 240V, but the watts are only 5600. Can you tell me the size of your garage?
    Thank you,
    Ashley – NewAir

  3. I got three hundred square feet of surface area;
    garage type area to heat;
    Insulation is poor or non existent.. but it is enclosed well enough to stop any drafts;

    Average temp is 50 degrees (F) outside , and I wish to attain 70 degrees inside roughly… Give or take a few degrees.

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