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.
This site is awesome. It provides relevant information in a concise, easy to understand format. Whoever organized the content of this site is to be congratulated. I never expected to find all the information I needed regarding heating my garage in one place.
Hello Scott, thank you, it means a lot.
This was handy, thanks.
I live in Minnesota and want to keep my 2 car garage about 45 degrees. It has an insulated door. 2 of the other walls and half of the 3rd wall are against our house. What is your estimate on heater size I would need.
Hello Thomas, it really depends on the insulation. Generally, if you just want to keep the garage at 45 degrees, you don’t need 30 BTU per sq ft. You would likely need 10 BTU per sq ft, or even less. Let’s say that you have a 500 sq ft 2-car garage; you’re looking at a 5,000 BTU heater. Even the standard 1,500W electric space heater (produces about 5,000 BTU/h heating output), running continuously, can keep your garage at a 45-degree temperature. Hope this helps.
I have a 24×24 detached garage -8ft ceilings. Fully insulated. Live in MN. What size heater and brand do you reccomend to keep it about 45- 50 in winter.
Everything I read tells the size heater for the space but does not include the temp that it keeps it. Dont need it real warm. Just want to be able to store things, paint..etc without freezing.
Hello Sue, to keep the garage just warm (the exact temperature depends on several complex factors), it’s usually recommended that you calculate 10 BTU per sq ft for an 8 ft ceiling garage. In your case, you have a 576 sq ft garage and would require a 5,760 BTU garage heater (using the 10 BTU/sq ft rule of thumb). Most electric heaters run on 1,500W and generate about 5,100 BTU. A good idea would be to just buy a simple 1,500W electric heater and see how warm does it keep your garage in the winter. If the heating is insufficient with just 1 unit, buy another one.
You can check the best garage heaters here. The King Electric units are considered the best; they are, however, a bit more expensive than other less reliable units. Hope all of this helps.
Hey Learn Matrix,
I’m trying to size a NAtural gas Heater for a 24×30 garage it has a 7 foot wall. With 2 uninsulated doors 6×10 the building has weak r13 and dry wall below the 5 oit mark and a fexposes light pannel above that’s fiberglass. Which is not insulated to include the exposed roof and side walls above.
I’m seeking to get it insulated… in your heat zones we might be 6 or 7 as we’re maybe 100 miles from the border of Wyoming in south eastern Idaho. Hvac.com recommended a 66,000 and 75,000 BTU solution. I’m seeking to heat the detached garage due to relocating a cottage bakery for Gommscookies.com there and may need yo keep it warm for the waters sake, but sufficient to produce in by day in the winter and to possibly have a fan solution in the summer for venting purposes.
Hello LaRoy, you have quite a lot of variables here. This is a 720 sq ft garage in 6 or 7 zone with below-average insulation (light pannels, fiberglass). You might need a bit more heating power here; about 60-80 BTU per sq ft. That would get you to the 43,200 BTU to 57,600 BTU range. The cited estimate would presume about 100 BTU/sq ft heating output; that’s a bit excessive. It’s quite possible that 50,000 BTU would be enough; let’s make it 60,000 BTU to be sure. Hope this helps.
Hi, I leave in Canada (Montreal) and typically we heat our garages at 8-10C, how does this affect the calculation?
Hell Karl, you will need less BTU per sq ft. Depending on several factors, you can shoot for 10 or maybe 20 BTU per sq ft. That means you would need about 5,000-10,000 BTU per 500 sq ft garage.
12ft by 24ft, 12 ft peaked ceiling, zone 4. Bare wood walls. Zero insulation. Recommendations. Thinking 36000, used as a den, partial living space.
Hi Shawn, zero insulation can increase the BTU requirements for heating a garage by a lot. Basically, you have a 288 sq ft garage, with a 12 ft ceiling (50% above average 8 ft ceiling). Given Zone 4 but no insulation and 50% higher ceiling, you probably have to use up to 80 BTU per sq ft, especially if you want to use the garage as a partial living space.
For a 288 sq ft garage, 80 BTU per sq ft comes to 23,040 BTU. So, 36,000 BTU would be a bit too much. 24,000 BTU would make sense. Hope this helps.
We live in climate zone 6. How many btu would we need to keep our 3 car garage heated to 40 degrees F in winter? Outdoor temperatures can drop to minus 20 F in the dead of winter. The garage walls and doors are insulated. One side of the garage adjoins the heated house. Living space above the garage is not used in winter, but it is heated to 60 F to keep the pipes from freezing.
Hi Marc, in climate zone 6, you would need 55 BTU per sq ft to keep the temperature at about 72 degrees F. Now, if you only need 40 degrees F temperature, you would need a lot less. Those -20 degree F in the winter are quite severe. Nevertheless, something in the neighborhood of 15-25 BTU per sq ft should be sufficient. If you have a 750 sq ft 3-car garage, that would be anywhere from 11,250 to 18,750 BTU (very rough estimates). So, not all that many BTU, but still, you would need about 15k BTU. Hope this helps.
Hi, I have a 720 square foot garage with a 12’-8” ceiling, with a second floor that will be unheated. I used 12” I-trusses for the ceiling that will be at R-30-40, and 2×6 walls at R-21. What would you recommend for BTU, to keep it at 50 degrees during the winter, and bumping it up to 65 when working in it.
Hi Mike, alright, we are talking about a well-insulated 720 sq ft garage that doesn’t need to be heated up to 72 degrees. Given the more than 50% higher ceiling height than average, you can take anywhere from 10 to 20 BTU per sq ft for heating. That would yield a heat load requirement from 7,200 BTU to 14,400 BTU. The simple solution would be to use 1500W electric heaters; one generates about 5,118 BTU. They are extremely cheap, you can just buy two of them and use them when needed, no installation required. Hope this helps.
Hello,
I have a 32 wide x 30 foot deep detached garage. Ceiling is 8 foot 9 inches. It is built into a grade with an 8 foot concrete wall along the backside and steps down on the right and left to 6 feet then 4 feet with just the front fully exposed. It is 2×6 construction insulated in the step down walls and has 8 foot and 16 foot garage doors insulated at R18. The ceiling is non insulated web truss 21 inches deep and the room above is fully insulated and kept heated with a Rinnai heater at 65 degrees to keep the pipes from freezing. I would like to keep the garage at the same 60 degrees I live in zone 6.
Thanks,
Warren
Hi Warren, thank you for so much details. Alright, we are talking 960 sq ft garage with 8 3/4 ft ceiling height, Zone 6, and quite solid insulation for a detached garage. For Zone 6, we would take 55 BTU per sq ft for 8 ft ceiling height. However, the goal here is elevate the temperature only to about 60 degrees, instead of 72 degrees. That means you can lower the BTU per sq ft quite significantly; to 20-30 BTU per sq ft.
Given that range, you would need anywhere from 19,200 BTU to 28,800 BTU to adequately heat the garage. That means that something like Rinnai EX22CTWP space heater (this one) with 20,700 BTU should be sufficient. Hope this helps.
Thank you!
I have a 20×18 garage with a 10′ ceiling, or 3600 cubic feet. The door is insulated at 13.4R. nothing else is yet. How many btu do I need to get 70 degrees?
Hi Bob, alright, this depends on where you live (Florida vs. Illinois, for example, would be a big difference). If you just go with a median of about 45 BTU per sq ft and you have 20×18 = 360 sq ft garage, you would need about 16,200 BTU of heating output. That’s either a 15,000 BTU heat pump or three 1,500W electric heaters (each of them makes about 5,100 BTU of heating output). Hope this helps.