Heating Load Calculator
Estimate the heating load for a room or building from floor area and insulation level.
This is a rule-of-thumb estimate from floor area only. A proper heat-loss (Manual J) calculation accounts for insulation R-values, air leakage, window area, orientation, and the outdoor design temperature for your climate zone. Consult a licensed HVAC professional before sizing equipment.
How it works
- 1Enter the floor area of the space in square metres or square feet.
- 2Select the insulation/climate category — 70 W/m² (well insulated, mild) to 150 W/m² (poor, cold).
- 3The calculator multiplies area × factor for the heating load in kW and BTU/h.
Use cases
- Sizing a radiator or heat pump for a new room before consulting an engineer.
- Comparing heating needs of a well-insulated extension and an older space.
- Converting a kW heating load to BTU/h for imperial-rated equipment.
Frequently asked questions
How is heating load found from floor area?
Load (W) = floor area (m²) × factor (W/m²). A 50 m² room at 100 W/m² needs 5000 W (5 kW). The factor bundles insulation quality and climate severity.
How is this different from a Manual J calculation?
Manual J is the ACCA standard for residential heat loss — it accounts for surface R-values, window areas, infiltration, duct losses, and design temperatures. Treat this tool as a planning figure, not a design spec.
How do I convert kW to BTU/h?
1 kW ≈ 3412 BTU/h (watts ÷ 0.29307). A 6 kW boiler delivers about 20,470 BTU/h; both units are shown.
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