No one wants a cold garage or shop. To avoid the cold, you will need some kind of heating. If you’re planning to heat your garage with central heating, garage heater, space heater, or a mini-split heat pump, you need to first answer one key question:
“How many BTUs do I need to heat my garage?”
The size of the heater (or heating output measured in BTUs or watts, to be exact) matters. Adequately quantifying how many BTUs you need will primarily depend on 2 factors, namely:
- Size of a garage. Square footage and ceiling height are key metrics here; from there you can calculate how many cubic feet of air in the garage you’ll have to heat. Obviously, you will need fewer BTUs to heat a 1-car garage than for a 2-car garage, for example.
- Your climate zone. In the north, you have a colder climate and you’ll need more BTUs to adequately heat a garage. Even well-insulated garages in the north will require more heating than bad-insulated garages in the south. Example: Garage in Texas (65°F average winter temperature) will require less heating BTUs than Garage in Minnesota (50°F average winter temperature).
To make the calculation as easy as possible, you can use the garage BTU heating calculator that will find at the end of the article (first we need to check the inputs; square footage, ceiling height, and climate zone). Here is a screenshot of what this calculator looks like:
For adequate estimation of how many BTUs you need to heat a garage, you will need to:
- Measure your garage. Length x width will give you the total square footage. Ceiling height x square footage will give you the total volume of the air in the garage.
- Identify your climate zone. Below you will find a climate zone map; you just need to figure out in which climate zone you are located (it’s based on average temperatures). This will help you figure out how many BTU of heat per square foot of the garage.
We will help you along the way. First, however, let’s look at the summary of heating output needed to heat a 1, 2, 3, 4-car garage:
1-Car, 2-Car, 3-Car, 4-Car Garage BTU Requirements (Rough Estimates)
We can roughly estimate how many BTUs you need to heat a garage by using a heating BTU calculator. Basically, you will need anywhere between 30 BTU to 60 BTU to adequately heat a garage; based on where you live.
We will go into the detail you how you pinpoint the BTU requirements down to 1,000 BTU further below (you will find a garage heating calculator and climate zone map to help you out). Here are the outtakes:
|Size Of Garage:||Warm Climate (30 BTU per sq ft):||Average Climate (45 BTU per sq ft):||Cold Climate (60 BTU per sq ft):|
|1-Car Garage (250 sq ft):||7,500 BTU||11,750 BTU||15,000 BTU|
|2-Car Garage (500 sq ft):||15,000 BTU||22,500 BTU||30,000 BTU|
|3-Car Garage (750 sq ft):||22,500 BTU||33,750 BTU||45,000 BTU|
|4-Car Garage (1,000 sq ft):||30,000 BTU||45,000 BTU||60,000 BTU|
Here we predispose average sizes of 1, 2, 3, 4-car garages. The ceiling height is 8 ft; if you have a 7 ft garage ceiling height, you will require a good 10% fewer BTUs to properly heat it in the winter.
Example: How many BTU for a 2-car garage? In an average climate, you will require about 22,500 BTU for a 2-car garage.
These are ballpark figures. To figure out how big a heater you will need for your specific garage, you can use the garage heater sizing calculator below. But first, let’s look at climate zones; you will need to know yours in order to adequately size a garage heater.
Climate Zones For Garage Heating
The colder it is, the bigger heater you will need to keep your garage warm. That goes without saying. The real question is quantification, namely:
“How many BTU per sq ft do I need to keep my garage warm?”
Now, you might have seen a simplistic equation for that. It’s this one:
(Cubic Feet Of Air) x (Desired Temperature Change) x 0.133 = Required BTUs
It’s simple enough but doesn’t really give realistic estimates for garage heating primarily because it doesn’t account for where you live (climate zone).
To truly get adequate estimates of exactly how many BTU you need for garage heating, we should use the Climate Zone map by the Office of Energy Efficiency & Renewable Energy:
You need to identify in which climate zone your garage is located. Example: Most of California is Zone 3, Southern Texas is Zone 2, and most of Illinois is Zone 6.
Depending on the climate tone, you will need to the following number of BTUs to properly heat your garage:
|Climate Zone||BTUs Per Sq Ft|
|Climate Zone 1||30 BTU per sq ft|
|Climate Zone 2||35 BTU per sq ft|
|Climate Zone 3||40 BTU per sq ft|
|Climate Zone 4||45 BTU per sq ft|
|Climate Zone 5||50 BTU per sq ft|
|Climate Zone 6||55 BTU per sq ft|
|Climate Zone 7||60 BTU per sq ft|
This predisposes 8 ft garage ceiling height. In the garage heating calculator below, you can lower this to lets say 7 ft or increase it to let’s say 10 ft.
Example: How many BTU for a 30×40 shop? That’s a 1,200 ft shop or a 1,200 ft 5-car garage.
Well, it depends on the location (climate zone):
- Texas (Climate Zone 2): 1200 sq ft * 35 BTU/sq ft = 42,000 BTU.
- California (Climate Zone 3): 1200 sq ft * 40 BTU/sq ft = 48,000 BTU.
- Illinois (Climate Zone 6): 1200 sq ft * 55 BTU/sq ft = 66,000 BTU.
Example 1: How many BTU for a 30×40 shop? To keep this 30×40 shop or a huge 5-car garage warm, you will need 42,000 BTU in Texas and 66,000 BTU in Chicago, Illinois, for example. That’s quite a big difference; because the difference is how hot it is in Texas vs how cold it is in Illinois is big.
Example 2: How many BTU for a 40×60 shop? You will need double the BTUs as for the 30×40 shop. On average, you need about 100,000 BTU for a 40×60 shop.
This is a rough idea of how to size garage heaters. The easiest way is to use this calculator:
Garage BTU Heating Calculator
To calculate how many BTUs you need to keep the garage warm, just input square footage, ceiling height, and pick the climate zone.
When you figure out how many BTU you need, you can check out some of the best garage heaters here.
Secondary Factors Influencing Garage Heating Requirements
The calculator gives you an estimate of your heating requirements for a garage. Do note that there are some important secondary factors that influence exactly how many BTUs are needed to heat up the garage like:
- Garage insulation. Better insulated garages require less BTU than poorly insulated garages. How many BTU to heat an unisolated garage? Well, more, but quantifying how much more depends on how unisolated the garage is, and that’s difficult to determine.
- Closeness to the house (central heating). If a heated house is all around your garage, you will obviously need less heating.
- How much volume does the ‘crap we have in a garage’ make up? All that volume is hard-matter (cars, bicycles, tools, etc.) and not air that needs to be heated up. The more ‘crap’ we have, the lower number of BTUs we’ll need because there is less air to heat.
These factors are not included in the calculator above primarily because it’s near impossible to quantify them.
A Word On Electric Space Heaters (Watts To BTUs)
One of the most popular choices to heat a garage are electric heaters. Here we encounter a problem in sizing (due to different units): Output of electric heaters is given watts (Example: 5,000W heater), not in BTUs.
To get BTUs, you can use watts to BTU converter here. You can also calculate by hand using this formula:
1 Watt = 3.412 BTU
Example: How many square feet of garage will a 5000-watt electric heater heat?
You need to convert 5,000 W to BTUs. Essentially, 5,000W * 3.412 = 17,060 BTU. Such a heater will be enough to heat a 1-car and even 2-car garage.
King Electric produces the best electric garage heaters. They offer 5,000W, 7,500W, 10,000W, 12,500W and 15,000W models. To help you figure out how many watts you need to heat your garage, they created this neat infographic:
These are ballpark figures and they are pretty accurate. You can use them to adequately size garage heaters.
If you have any questions about garage heating requirements, you can use the comment section below and we can discuss what the best options for your specific situations are.