Garage Heater Sizing Guide: What Size Garage Heater Do You Need?

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When winter comes, cold weather brings low temperatures that require you to heat your home.

But almost no houses are built with heating inside their garages.

So if you want to keep working on projects in your garage, you’ll want to keep it at a comfortable temperature. 

Even if you don’t need your garage comfy, sometimes you just need to keep your garage above freezing temperatures.

Having the right-sized garage heater ensures that you’ll be able to crank out just enough heat for the situation.

In this article, I’ll go over what you need to consider when sizing a garage heater, and how to calculate the right size heater for your garage.

What to consider when sizing a garage heater

To figure out what size heater you need for your garage, you need to consider a few factors that I’ll explain below:

Size of the garage

The size of your garage is one of the most (if not THE most) important factor when sizing a garage heater.

Simply put, a larger garage will need more heat than a smaller garage.

In heating calculations, you also need to take into account the height of your garage. This is because hot air rises, so it’s important to take the ceiling height into account as well.

This means that when calculating the size of the heater you need for your garage, you need to measure the volume (ft3) of your garage.

Temperature inside the garage

The temperature inside your garage has a huge effect on what size heater you need.

More importantly, the temperature rise is what you need to consider.

The question to ask yourself is: “How warm do I need my garage to be?” Some people have workshops in their garage, so they need it at comfortable temperatures.

However, if you only need to keep your garage above freezing temperatures, then you won’t need as large of a heater. 

Here are a couple of examples:

  • If your garage is 30°F, then you only need to heat it about +15°F to bring it safely above freezing temperatures (30+10=45°F).
  • If your garage is 30°F, then you need to heat it about +40°F to bring it to comfortable working temperatures (30+40=70°F).

Simply put– if your garage is freezing cold, then you’ll need a larger heater to bring it up to comfortable temperatures.

Climate outside the garage

The weather outside has a huge effect on the temperature inside your garage. 

If you live in a cold climate, then you’ll have colder temperatures in your garage.

For this reason, you need to consider how cold it gets outside when figuring out how big your garage heater needs to be.

Insulation in garage

The insulation in your garage is another important factor.

If your garage is insulated, then you won’t need as much heating to keep it at a stable temperature.

A typical home will have some level of insulation in its walls and ceiling. But garages don’t have much insulation if any.

If you have a cold garage and plan to heat it to comfortable temperatures, then it may be worth it to invest in insulating your garage first.

Having a well-insulated garage will save you money on your heating bill since you won’t lose much heat to the outside.

How to calculate what size garage heater you need

There are a few things that you need to calculate the size of a garage heater:

1. Volume of garage

To find the volume of the garage, measure the sides of your garage. For a rectangular garage, you will need to measure the length and width of your garage. 

Then multiply the length and width to find the area of your garage.

After you find the area of your garage, measure the height of the garage.

Finally, multiply the area of your garage by the height of your garage to get the volume of your garage.

2. Temperature that you want your garage to be

The other thing you’ll need to figure out is exactly what temperature you want your garage to be.

  • For example, if you just need to keep your garage above freezing temperatures, then you won’t need much heat. In this case, a temperature of 45°F is a good starting point.
  • On the other hand, if you need your garage to be cozy enough to spend lots of time (like a workshop, for example) then you’ll need a larger heater to keep it warm. For keeping your garage warm, consider using a temperature of about 65-70°F

3. Lowest temperature outside

You’ll also need to do some research to find out the lowest temperature that it will reasonably be outside. This is important because the colder it is outside, the bigger the garage heater you’ll need.

For example, it’s much harder to keep a garage warm when it’s 10° versus 40°.

4. Insulation around garage

The last thing you need to know to figure out your garage heater size is how much insulation you have in your garage.

The amount of insulation in the walls and ceiling of your garage drastically affect how big of a heater you need.

The tricky part is knowing how much insulation you have.

This is where calculating garage heater sizes gets tricky– it’s tough to calculate how insulated a garage is without knowing exactly what kind of materials it’s made of.

Also, things such as windows will affect the insulation properties of a garage.

For this reason, our garage heater size calculator below is more of a rough estimation rather than an exact measurement. But it will get you on the right track as far as what size garage heater you need to be looking at.

Hi, my name is Trey Lewis and I’m the founder and chief editor at HVAC Training Shop. My goal for this website is to help homeowners troubleshoot and maintain their home’s HVAC systems. Whether it’s changing an air filter, troubleshooting a blower motor, or just buying a new humidifier, I want to make sure that you’re covered.

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