How Many Btus To Heat A 2 Car Garage: Estimate Heat Loss

Determining the appropriate BTU output for heating a 2-car garage is crucial for ensuring a comfortable and energy-efficient environment. The British Thermal Unit (BTU) measures the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Several factors influence the BTU requirement, including the garage’s size, insulation, climate, and desired temperature.

Calculating BTU Requirements

To calculate the approximate BTU requirement for your 2-car garage, consider the following steps:

1. Determine the Garage’s Volume: Measure the length, width, and height of the garage to calculate its volume in cubic feet. For a typical 2-car garage, the volume is around 1,000 cubic feet.

2. Estimate Heat Loss: The amount of heat lost from the garage depends on its insulation. A well-insulated garage with R-19 walls and R-38 ceiling insulation will have a lower heat loss than a poorly insulated one. Use the following table to estimate the heat loss per hour per square foot of surface area:

Insulation Level Heat Loss (BTU/hr/sq. ft.)
Poor (R-11 or less) 1.5
Moderate (R-13 to R-18) 1.0
Good (R-19 to R-24) 0.75
Excellent (R-25 or higher) 0.5

Calculate the total heat loss by multiplying the heat loss per square foot by the total surface area of the garage, including walls, ceiling, and doors.

3. Determine Temperature Difference: Calculate the difference between the desired indoor temperature and the average outdoor temperature during the coldest month in your area. For example, if you want to maintain a temperature of 50°F inside the garage and the average outdoor temperature is 20°F, the temperature difference is 30°F.

4. Calculate BTU Requirement: Multiply the garage’s volume by the heat loss and the temperature difference. This will give you the approximate BTU requirement in BTUs per hour.


For a 1,000 cubic foot garage with moderate insulation (R-15), a heat loss of 1.0 BTU/hr/sq. ft., and a temperature difference of 30°F, the BTU requirement would be:

BTU Requirement = 1,000 cubic feet x 1.0 BTU/hr/sq. ft. x 30°F = 30,000 BTUs per hour

Additional Considerations

In addition to the above calculations, consider the following factors when determining the BTU requirement for your 2-car garage:

  • Garage Usage: If you plan to use the garage for activities that generate heat, such as working on cars or painting, you may need a lower BTU output.
  • Ventilation: Proper ventilation is essential to prevent moisture buildup and air quality issues. Ensure your garage has adequate ventilation to avoid oversizing the heater.
  • Heater Type: Different types of heaters have varying efficiencies. Consider the efficiency of the heater you choose when calculating the BTU requirement.
  • Climate: The climate in your area will significantly impact the BTU requirement. Colder climates require higher BTU outputs.

By following these steps and considering the additional factors, you can determine the appropriate BTU output for heating your 2-car garage, ensuring a comfortable and energy-efficient environment.