how many btus to heat a 2 car garage

[DelClayton]

The number of BTUs needed to heat a 2-car garage depends primarily on its size, insulation, and your local climate. A common rule of thumb is 20-30 BTUs per square foot for a moderately insulated garage in a cold climate. For a typical 2-car garage (around 400-600 sq. ft.), this translates to a heater between 8,000 and 18,000 BTUs. However, this is a starting point; poor insulation or very cold winters can double the requirement.

The most accurate way to calculate your need is by considering three key factors: the garage's square footage, its insulation level (R-value), and the temperature rise you desire (the difference between outside and inside temperatures). Here's a breakdown of how these factors influence the BTU requirement:

• Square Footage: This is the baseline. Multiply the length by the width of your garage.
• Insulation (R-value): This is the most critical variable. A well-insulated garage with sealed doors dramatically reduces the heat load. An uninsulated garage loses heat rapidly.
• Climate (Desired Temperature Rise): If you want a 40°F temperature rise on a 20°F day (to reach 60°F inside), you'll need a more powerful heater than for a 20°F rise on a 40°F day.

For a more precise estimate, you can use the following calculation based on common building standards. The formula is: (Length x Width x Height x 0.133) x Desired Temperature Rise. The "0.133" factor accounts for standard insulation. For poor insulation, use 0.5; for excellent insulation, use 0.05.

Garage Size (ft)	Area (sq ft)	Insulation Level	Desired Temp Rise (°F)	Estimated BTU Requirement
20x20	400	Poor (Uninsulated)	30	18,000 - 24,000
22x24	528	Moderate	40	15,000 - 18,000
24x24	576	Good (Insulated)	50	12,000 - 15,000
20x20	400	Excellent (Heated Space)	20	5,000 - 8,000

Ultimately, if you're between two sizes, it's often better to choose the slightly more powerful unit. A heater that's too small will run constantly without reaching a comfortable temperature, while a slightly oversized unit will simply cycle on and off more frequently.

[DaisyAnn]

As a contractor who's installed dozens of garage heaters, I always ask two questions first: "What's the garage made of?" and "What are you doing out there?" An uninsulated metal building needs a beast of a heater—maybe 45 BTUs per square foot. A finished, insulated space needs far less. If you're just tinkering, 45-50°F is fine. If it's a workshop, you'll want 60-65°F, which demands more power. For a standard 24x24, start with a 15,000-18,000 BTU unit if it's insulated.

[Piper]

I went through this last winter. My 2-car garage is attached but had zero insulation. I bought a 10,000 BTU electric heater, and it struggled to make a dent on cold Wisconsin days. It ran nonstop and my electric bill spiked. I ended up insulating the walls and ceiling myself—it wasn't too hard—and then the same heater worked perfectly. My advice? Spend a weekend insulating first. You might find a smaller, cheaper heater does the job, saving you money in the long run.