What Size Heater Do I Need For My Garage?

Garage heaters are a perfect way to work comfortably in your garage for hours, even during the coldest winter days. But as great as they are, it’s still important to choose the right sized heater for your space. Purchasing the wrong garage heater for your area will cost you money is several ways. First off, if the model you buy is too small for your garage it will be inefficient and won’t be capable of providing adequate warmth. Plus, since it’s not capable of handling the size of your garage, the unit will continually work, driving up the operating costs.

And if you buy a unit that is too large for your garage, you’ll only be shelling out more money than is necessary. In this article, we’ll show you how to determine the size of the garage heater you’ll need to provide reliable, consistent heat all winter long. We’ll also show you how to setup your unit for maximum heating results. Once you finish reading through this article, you’ll not only know what size model you’ll need to buy but where in your garage to install it.

The Easy Way to Determine the Size of Garage Heater You Need

Luckily there are several ways to determine the ideal thermal output that your garage heater needs for optimal performance. The first way is the easiest and it’s smart to look into this method before deciding to use the calculation method. Simply measure the length and width of your garage and multiple these numbers. For instance, if your garage is 20 feet long by 20 feet wide, your garage has an area of 400 square feet.

Now you can simply go online and research the best models out there. In the past, many manufacturers only specified the BTUs of their garage heaters (click here for our top list). But today, some of the top brands actually specify the area of heating coverage that their models are capable of. If the model that you’re thinking of purchasing lists the square footage that their models are able to efficiently heat, then you would simply have to find a unit that can adequately cover the size of your garage.

For the 400 square foot garage that we mentioned above, you’d want a garage heater that is capable of handling an area slightly larger than your garage’s actual size, perhaps around 500 square feet. This allows for a safety cushion for those unusually cold days. And keep in mind that if your garage has inadequate insulation, you might want to consider a model that is capable of handling an even larger area simply to offset the loss of heat that the lack of insulation will cause.

Heater Sizing Calculator

If the brand you’re looking at doesn’t specify the size of the area that their units are capable of heating, or if you simply want a more exact answer, there’s an easy formula that you can follow. All you need is a pencil, paper, tape measure, and a calculator. The first thing you need to do is determine the square footage of your garage. To do this, you measure the length of your garage by its width. So, if you have a garage that measures 15 feet long by 10 feet wide, the calculation would be 15 x 10 = 150 square feet.

Now, since you need to take the total area of your garage into account, you need to find out its total cubic feet. The way that you can do this is to measure the height of the ceiling and then multiply it by the square footage that you just came up with. Using our example of a 150 square foot garage, if it had 10 foot high ceilings, the calculation would be 150 x 10 = 1,500 cubic feet.

Now, you’ll want to figure out the temperature rise that you want your new garage heater to be capable of. To do this, take the lowest winter temperature that normally occurs in your region and subtract it from the temperature you’d like to maintain within your garage. For instance, if your region normally has a lowest temperature of around 25 degrees Fahrenheit and you want to maintain a temperature of 65 degrees, your calculation would be 65 – 25 = 40.

The next step is to calculate the BTUs or British Thermal Units that are needed to achieve this temperature rise. The first step to this is to factor in the level of insulation that your garage has. As mentioned before, the insulation of your garage needs to be taken into account in order to work in aspects such as heat loss or retention.

You’ll use one of the following numbers as a variable: use “5” for no insulation, “1.5” for a garage that has a little insulation, use “1” for average insulation, and use “0.5” for a garage with excellent insulation. With this number decided, you’ll multiply the insulation quality variable by the total cubic feet by the desired height rise.

You’ll then divide this number by a BTU factor of 1.6. This will give you the BTUs required. Using the previous example, and assuming that your garage has little insulation, the calculation would be (1.5 x 1,500 x 40) / 1.6 = 56,250 BTU. Finally, you need to include a buffer to this number to act as a safety margin.

This will ensure that the garage heater you buy is capable of performing efficiently on any day that is colder that your normal lowest temperatures. To do this, add 10% to the BTU number. So, using our example, you’ll simply perform these two steps: first determine that 10% of the BTU is by multiplying the BTU by .10, so it would be 56,250 x .10 = 5,625.

Then just add that number to the original BTU result, which would look like this, 56,250 + 5,625 = 61,875. That’s it. In about 5 minutes you determined that the ideal garage heater for this specific garage would have an hourly BTU output of 61,875 BTU.

Most Efficient Way to Heat a Garage

Now that you’ve determined how many BTUs your garage heater needs to produce for efficient heating performance, you need to install it. You want to maximize the unit’s ability to effectively heat your garage. To do this, the recommendation is to place the heater at the back wall facing the garage door. This is where most heat is lost so it makes sense to have the heat originate at the most insulated section of your garage and flow out in that direction.

Another thing to keep in mind is that if you have a forced-air model, make sure that the flow path is clear so that the warm air produced by your garage heater circulates throughout your workspace. Also keep in mind that, regardless of the style of heater you choose to purchase, you want to ensure that there are no objects within 3 feet of the unit for safety and to reduce the risk of overheating objects.

Determining what size garage heater you need might seem like a complicated task but with a tape measure and calculator, it can be done in minutes. And while it’s easy to just guess and buy the model you think is right for you, by going through these simple steps you can determine the exact BTU output that you need. This way, you can rest easy knowing that your garage will be toasty and warm even during the coldest of winter days.

About the Author

Bob Robinson has been a tool enthusiast and lawn care expert for the past 11 years. First working with John Deere to reduce their impact on the environment, whilst building his love for writing in his spare time. Now, Bob runs the editorial team at BestofMachinery and tends to his garden in his spare time.

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