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The right garage heater size for most shops is 30 to 50 BTUs per square foot. A well-insulated shop needs about 30 BTU per square foot, an average shop about 40, and a poorly insulated or high-ceiling shop about 50 or more.
A common 24-by-24 shop of 576 square feet usually needs 30,000 to 50,000 BTUs. In cold Idaho Falls winters, size toward the top of the range. If you want it done right, our team installs gas unit heaters sized for your space.
Key Takeaways
- Rule of thumb: 30 to 50 BTUs per square foot, set by how well the shop is insulated.
- Common sizes: a 2-car or 24-by-24 shop needs about 30,000 to 50,000 BTUs; a 3-car or large shop needs 50,000 to 75,000 or more.
- High ceilings: add about 25% capacity for ceilings taller than 10 feet.
- Idaho cold: add roughly 10% for sub-zero Idaho Falls winters.
- Size matters both ways: an oversized heater short cycles; an undersized one never keeps up.
What Size Gas Heater Do I Need for My Shop?
The quick answer is 30 to 50 BTUs per square foot of floor space. The exact number depends on insulation. Bare block walls and an uninsulated overhead door lose heat fast, so a drafty shop lands near 50 BTUs per square foot. A tight, insulated shop with a sealed door can get by near 30.
Insulation is the biggest lever. Sealing and insulating a space is usually cheaper than buying and running a bigger heater forever. Tighten the shop first, then size the heater.
How to Calculate BTUs for Your Shop
You can size a shop heater in four steps. Here is the method a technician uses.
- Measure the floor area. Multiply length by width. A 24-by-24 shop is 576 square feet.
- Pick a BTU factor. Use 30 BTU per square foot for a well-insulated shop, 40 for average, and 50 for poorly insulated.
- Adjust for ceiling height. Standard sizing assumes an 8 to 10 foot ceiling. Add about 25% for taller ceilings, since you are heating more air.
- Adjust for the Idaho climate. Add roughly 10% for the deep cold we see in Southeast Idaho.
Worked example: a 576 square foot shop with average insulation at 40 BTU per square foot needs about 23,000 BTUs. Add 10% for Idaho Falls winters and you land near 25,000 to 30,000 BTUs. If the same shop is drafty, use 50 BTU per square foot and plan on roughly 30,000 to 35,000 BTUs.
Garage Heater Size by Shop Size
Use this chart as a starting point, then adjust for ceiling height and insulation. These ranges assume a standard ceiling in a cold climate.
| Shop size | Approx. square feet | Well insulated | Poorly insulated |
|---|---|---|---|
| 1-car / small | 200 to 300 | 10,000 to 15,000 BTU | 15,000 to 20,000 BTU |
| 2-car / 24×24 | 400 to 600 | 25,000 to 35,000 BTU | 40,000 to 50,000 BTU |
| 3-car / large | 700 to 900 | 35,000 to 50,000 BTU | 50,000 to 75,000 BTU |
| Oversized shop | 1,000+ | 50,000+ BTU | 75,000+ BTU |
Natural Gas vs Propane Shop Heaters
Most shop heaters run on natural gas or propane, and the BTU math is the same for both. If you have a natural gas line at the property, natural gas is usually the lower running cost and the simpler install. If you are off the gas main, propane is the common choice and burns a little hotter per unit.
Either way, a gas shop heater needs correct venting to prevent carbon monoxide and a safe gas connection, which is a job for a licensed installer. Ridgeline handles shop heater installation and the gas line work that goes with it.
Why Right-Sizing Matters
Bigger is not better with a shop heater. An oversized unit heats the air fast, shuts off, and short cycles, which leaves the floor and your tools cold while wearing out the ignition. An undersized unit runs nonstop and still never reaches temperature on the coldest Idaho days.
Getting the size right the first time gives you even heat, lower fuel use, and a longer-lasting heater. When you are weighing options, our professional heating services team can run the numbers for your exact shop. A ductless system is also worth a look; see our ductless heating options.
Garage Heater Size FAQs
How many BTUs do I need to heat a 24-by-24 garage?
A 24-by-24 shop is 576 square feet. At 40 BTU per square foot for average insulation, that is about 23,000 BTUs, and many owners choose a 30,000 to 50,000 BTU heater to cover cold snaps and high ceilings. In Idaho Falls, sizing toward 45,000 to 50,000 BTUs is common for a drafty or tall shop.
What is the recommended size heater for a 2-car garage?
A typical 2-car garage of 400 to 600 square feet needs roughly 30,000 to 50,000 BTUs. Use the lower end if the space is well insulated and the higher end if the walls, ceiling, or door are not. Add about 25% if the ceiling is taller than 10 feet.
How many square feet will a 50,000 BTU heater heat?
A 50,000 BTU gas heater comfortably heats about 1,000 to 1,500 square feet in a well-insulated space, or closer to 1,000 square feet in a drafty one. In a cold climate like Idaho Falls, plan on the lower figure so the heater is not running at full output all winter.
Is it better to oversize a shop heater?
No. Slight extra capacity is fine, but a heater that is far too large short cycles, wastes fuel, and heats unevenly. A properly sized unit runs steadier, costs less to operate, and lasts longer. When in doubt, have the load calculated rather than guessing big, the same way we size a whole-home HVAC system.
Get the Right Shop Heater for Your Idaho Falls Space
Not sure which size fits your shop? Call Ridgeline Heating and Cooling at (208) 521-2041 and a local Idaho Falls technician will size the heater to your square footage, ceiling height, and insulation, then handle the install and gas line safely. Request a free shop heating quote today.
Ridgeline Heating and Cooling
370 College St, Idaho Falls, ID 83401
Phone: (208) 521-2041
Hours: Monday to Friday, 6:00 AM to 5:00 PM
Website: https://idahofallsheatingandcooling.com/
Idaho HVAC license #050089
Serving Idaho Falls and surrounding Southeast Idaho.
