Once you decide to turn your normal garage into a heated garage, you have to figure out what size heater you need and how many of them you need. There are a number of factors that will help you decide.

To start, you’ll have to address the actual size of your garage. From there, you can work out your current climate alongside the ideal temperature range you’re seeking.

All of this will allow you to figure out how many BTUs you’ll need to heat. BTUs, otherwise known as British Thermal Units, indicate how much heat the heater actually produces.

## Measure for Square Feet

Measuring the square feet of your garage may be the simplest step you can take to finding out what size heater and how many you’ll need to properly warm the area up. This is because quite a few heaters these days indicate the average square feet they’re capable of handling.

To get the square feet, you’ll just want to measure the length and the width of your garage. From there, multiply the length by the width, and the resulting number is the square feet.

For example, say you wind up with measurements of 12ft. by 24ft. You’ll get the following equation: 12 x 24 = 288. So, your garage will have an area of 288sqft.

## Measure for BTUs

In other cases, you may find garage heaters that don’t spell out how much heat they put out in square feet. You’ll have to take things a step further in this case.

Using the previous information for a 12×24 garage, you’ll take the square feet and multiply it by the height of the ceiling to get the total cubic footage.

On average, a ceiling in a garage is around 8ft. So, you’ll get the following: 8 x 288 = 2,304 cubic feet.

Once that’s settled, you’ll have to do some research and a few more calculations to continue on. First, figure out the ideal temperature rise you want from your garage. You’ll do this by figuring out the lowest seasonal temperature normally found in your region.

Whatever number you get there, you’ll want to subtract it from the temperature you wish for your garage to have.

Let’s give another example to help. If your region has an average seasonal low of around 20 degrees Fahrenheit, but you want your garage to maintain a steady temperature of 68 degrees Fahrenheit, your equation will look like this: 68 – 20 = 48.

Now, we can get to work on calculating the BTUs. You’ll need to find out just how many BTUs it will take to raise the temperature in your garage to the number you want.

The first thing you’ll do here is to find out what type of insulation your garage has. Insulation is what will help you figure out what type of heat loss you may experience as well as the retention.

There are four easy variables you can use when it comes to insulation:

- A variable of “5” is used when there’s no insulation
- A variable of “1.5” is used when there’s little insulation
- A variable of “1” is used when there’s an average amount of insulation
- A variable of “0.5” is used when there’s excellent insulation

You’ll use the insulation variable and multiply it by the total cubic feet (2,304 from our example) and by the heat temperature rise you wish for (48).

The equation isn’t finished just yet though. You then want to divide the resulting number by a BTU factor of 1.6.

So, say you have a garage that has an insulation variable of “0.5”. Using the other numbers from our example, your equation will look like this: (0.5 x 2,304 x 48) / 1.6 = 34,560 BTUs.

Hopefully, you’re still following along because we’re still not quite finished. You will now want to add on 10 percent to the BTUs required. This add-on will offer you a safety net of sorts to give you a bit more heat if the temperatures drop unusually low.

For the above example, to truly figure out how many BTUs to heat to keep your garage warm even in extreme situations, you’ll start with this equation: 34,560 x .10 = 3,456. The result is what you will add to the original BTUs: 34,560 + 3,456 = 38,016 BTUs.

It may seem like a lot of work, but with a measuring tape, calculator, pencil, and paper, you should be able to get all of this done in less than 10 minutes.

## Number of Heaters to Use

In all reality, you can get away with purchasing just one heater to keep a steady stream of warmth in your garage. However, there are some cases where having more than one heater may benefit you more in the long run.

Say you have a large garage with some rather poor insulation or even no insulation at all. You can opt for purchasing larger heaters, but that can get expensive and may not even have the BTUs you’ll need to get the temperature you want.

In this case, you can purchase two smaller heaters that can reach a BTU that’s slightly more than the range you’re after. Of course, when the time comes to make a purchase make sure you check out our buying guide at This Electric Home to find the best garage heater to suit your calculations.

Honestly, even if the area has good insulation, you might still need to purchase more than one heater if your garage is great in size and you plan on heating the entire area. It can still prove too much for one heater to manage.

When you’re figuring this out, be sure to keep in mind the type of heater you’re using. For instance, in the case of radiant heaters that generally focus heat on a specific area, they can be placed anywhere. It can be easier to make use of more than one of these types.

With something like a convection heater, they tend to work best on the floor, so that can limit how many of them you can use depending on what exactly you have in your garage.