Workshop heat sizing
Garage heater BTU calculator
Estimate BTU/h for a garage, workshop, or cabin from length, width, height, insulation, and temperature rise. Maps the load to a 2, 5, or 8 kW diesel heater class — or says NO_MATCH.
Result
BTU/h = ft³ × insulation factor × ΔT (°F). Insulation 1=excellent (0.093) … 5=very poor (0.173). 1 kW ≈ 3412 BTU/h. Rule of thumb only — not Manual J.
How this calculation works
Measure the heated volume in cubic feet. Multiply by an insulation factor that reflects walls, ceiling, and door leakage, then by how many degrees Fahrenheit you want to raise the space above the design outdoor temperature. The calculator converts that BTU/h load to kilowatts and names the smallest portable diesel air-heater class (2, 5, or 8 kW) whose ceiling clears the estimate. Loads above 8 kW return NO_MATCH instead of forcing a product.