BTU & Heat Loss Calculator

Quickly calculate heat loss and find the right radiator size for your space.

*Results are estimates for informational purposes only. Oswald Supply advises consulting a licensed heating contractor to verify your project's exact heating requirements.
Windows/DoorsH.M. WallH.M. CeilingH.M. FloorH.M. InfiltrationH.M.
Single67 No Insulation15 3 Inches5 No Insulation4 1 1/2 Air Change1.61
Single Insulated41 2 inches6 6 Inches4 Overhang 3"5 1 Air Change1.07
Storm34 4 inches5 9 Inches3 Overhang 6"3 3/4 Air Change0.81
Double Insulated30 6 inches4 10 Inches2 Overhang 9"2 --

Total Room/Building:

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Heat Loss Calculator

This tool helps you estimate the heat loss of your room or home and suggests a suitable BTU range and radiator size based on your input.

The calculation is based on standard Heating Multipliers (H.M.) in BTU/hr using a 60°F temperature difference.

Please note: Results are estimates for informational purposes only. For precise sizing and installation, Oswald Supply recommends a detailed heat loss calculation by a licensed heating professional. Oswald Supply is not liable for sizing errors. .

How the Calculation Works

The tool calculates your room's heating requirements using the following steps:

  1. Surface Area: Measures the total wall area (Length × Height).
  2. Net Wall Area: Subtracts window and door areas from the total wall area.
  3. Ceiling & Floor Area: Adds the ceiling and floor square footage to the equation.
  4. Insulation Factors: Applies specific Heating Multipliers (H.M.) based on your insulation quality.
  5. Air Change: Factors in heat loss from air leakage based on the room's overall condition.
  6. Final Recommendation: Combines these totals to estimate heat loss and match you with the correct BTU range and radiator size.