As the weather starts to drop, you might start to think about how you’re going to keep your garage warm. After all, the central heating in many homes doesn’t reach the garage, yet you’re going to have to work in that space all year round. As such, it’s important not only that you get a heater, but also that you get the right heater for that space. Doing so, however, does require understanding both that there are several kinds of heaters out there and that you’ll have to be able to calculate precisely what size of heater is going to be right for you.
A Quick Note on Terminology Relating To Garage Heaters
Heating has its own special language, as does any other kind of specialized science. You’re going to need to know that language long before you make a purchase, as being fluent in it will help you to make a better choice when it’s time to buy. Of all the very important terms that you’re going to need to learn, perhaps the most important will be wattage.
Wattage, usually written as watts on the box, is a more complex term than you might think. If you dig into the science, you’ll see that a watt is essentially equal to a joule per second. Wattage isn’t just measured in watts, though – it’s also measured in amperage and voltage. As a consumer, you’re going to need to be aware of what all of these terms mean for you when you finally decide to start shopping.
The other big term that you’ll need to know is the British Thermal Unit. The BTU, as it is more commonly known, is the measure of energy that’s needed to heat up a pound of one degree. A BTU is also around 1,055 joules, while a watt is around three and a half BTUs.
BTUs are incredibly important when you’re looking at heaters. You’ll need to know the amount of BTUs that the heater puts off in order to determine whether or not you have the right size of machine to effectively heat up your garage. In addition, you’ll also need to be able to determine how much you need to heat up your space in order to figure out the exact output that you’re going to need from your heater.
Figuring out how much heat you need only involves some fairly simple math. You’ll simply take the ideal temperature that you’re trying to reach and subtract the actual outdoor temperature in which your heater will be working. If you want to keep your garage at a balmy seventy-degree and it’s forty degrees outside, you’ll need to be able to raise your temperature thirty degrees.
The final big terms you’ll need to know related to your insulation. You’ll need to understand R-value, for example, which is simply the value used to determine the efficacy of your insulation. If your insulation has a higher R-value, your garage will lose less heat over time. As such, you’ll want to know exactly where your insulation lies on that scale in order to determine how much heat your garage is going to lose while your heater is running.
The Types of Heaters
Once you’re familiar with the language you’ll need to use, you’ll be able to start shopping. Fortunately, there are really only two major types of garage heaters at which you’ll be looking – electric heaters and gas heaters. Electric heaters tend to be more common and function through heating up the air around the heater by running electricity through a metal implement of some sort.
Most electric heaters also incorporate a fan into their construction. The units make use of the fan to move air around your garage, which helps keep the heat moving around the space. Electric heaters tend to be a good choice when you’re working in a space that has poor insulation, which tends to be common in most garages.
Gas heaters work very differently than electric heaters. These units burn fuel, which is usually either natural gas or propane, in order to heat up your space. Like electric heaters, these units also use fans to blow the hot air generated by combustion throughout your garage. These heaters tend to be much more effective when they’re used in spaces that are well-insulated. Check out our guide on how to properly insulate a garage.
Gas heaters are almost always stronger than electric heaters, with many of them designed to heat up much larger spaces and to function when the weather gets much colder. They are not, however, quite as efficient as electric heaters and they do tend to require much more energy in order to heat up your garage. Gas heaters waste an awful lot of their fuel (nearly twenty percent) when they’re working, which also means that you’re going to need good ventilation if you’re using one of these devices. Electric heaters also tend to shine when the budget is an issue, as these units typically cost much less than their gas counterparts. Looking for the right electric heating source? Check out the review we made of the the best outdoor heaters that work perfectly well for garages.
Figuring Out the Right Heater Size
Now that you know the types of heaters out there, you can start thinking about the size of the heater that you need. You’re generally going to use one of two methods here – either watts or BTUs. Watts tend to be the easiest calculation method for most, as the general rule of thumb here is that you’ll need ten watts for every square foot of space you need. As an example, a space that’s one hundred square feet is going to need about one thousand watts in order to work properly.
Unfortunately, gas units aren’t usually rated in terms of watts. Gas heaters are rated in terms of BTUs, so you’re going to need some slightly more difficult math to figure out exactly what you need here. You’ll need to use the same formula that you used to calculate your necessary wattage, then you’ll need to multiply the result by 3.41. If you’re heating a one hundred square foot space, then, you’re going to need a heater that generates about 3410 BTUs to stay happy.
Of course, all of this is actually just an estimation of what you need. If you’re trying to be as precise as possible, you’ll actually need to calculate the volume of air that’s in your garage, which means multiplying the length and width of your garage space by its height. If you’ve got that ten-by-ten garage from before, you’ll multiply that by its eight-foot ceiling to get eight hundred cubic feet of air that you need to heat up.
As an aside, you’ll also need to take the R-value of your insulation into account here. To figure this out, you’ll need to know precisely what kind of insulation you have so that you can get this number as close as possible. If you’re not sure, you can cheat by assigning basic values for certain types of insulation. Great insulation has a value of .5 while no insulation at all has a value of 5, with everything else falling somewhere in between. From here, you’ll launch into your next bit of math.
You’ll need to take the R-value of your insulation, multiply it by the cubic volume of air in your garage, and then multiply it again by the amount you’ll need the temperature to change in your garage when the heater is running. Once you divide that number by 1.6, you’ll know precisely how many BTUs you need.
Confused? Let’s look at the math.
Let’s say that you have great insulation and a 10x10x8 garage that you’ll need to raise the temperature by ten degrees. Since we’ve done the work to figure out the cubic volume of air before, we can put together an equation that looks something like this:
(.5 * 3410 * 10)/1.6
A quick trip to the calculator will tell us that you need about 10656 BTUs in order to get exactly what you want from your heater.
Knowing What You Need From your Heater
Honestly, figuring out the size of the heater you need isn’t that hard. If you know at least a little bit about how heaters work and what numbers to look for, you’ll be able to figure out exactly what you need. Determining whether you need gas or electricity is, of course, a matter of preference here as well, but it’s not something over which you ought to lose sleep.
Don’t be afraid to do the math to figure out how big of a heater you need. Doing so will not only ensure that you get the best heater for your space, but it will help you to make sure that you don’t waste energy heating up your garage.
Frequently Asked Questions
1. What size heater do I need for a 2 car garage?
This largely depends on the actual cubic footage of your garage. On average, a two-car garage is going to be somewhere around 6480 cubic feet. If you’re looking to be as precise as possible here, you’ll need to multiply that number by the R-value of the insulation in the garage and the difference in temperature that you’re trying to generate, then divide it all by 1.6 in order to get the precise number of BTUs that you need.
2. How do you size a garage heater?
Sizing a garage heater can be done in a few ways. If you’re going with the simplest method, you’ll just want ten watts for every square foot. If you want to go complicated, you multiply the cubic volume of air inside the garage by the R-value of the insulation and the temperature rise needed, then divide that all by 1.6 to figure out how many BTUs you need.
3. How many BTUs do I need for a 1000 sq ft garage?
If you’re using the simplest method, you’ll multiply the square footage by ten to get the wattage you need, then multiply it again by 3.41 in order to get the BTUs needed. As such, you’ll need around 34,100 BTUs for your garage space.
4. How many BTUs does it take to heat a 4 car garage?
It depends on the size of the garage. If a four-car garage is somewhere around 1056 square feet, you’ll need ten watts for every square foot. This means you’ll need 10560 watts, which then has to be multiplied by 3.41 in order to get the BTUs you need. As such, you’ll need around 36000 BTUs.