BTU for Room Heating Calculator
Heating BTU/hr = ft² × insulation factor × ΔT.
Result
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How to use this calculator
- Enter room area.
- Pick insulation level.
- Enter the design ΔT (typical: 50-70°F).
About this calculator
Heating load depends on three factors: room size, how well-insulated the room is, and how cold it gets outside. ΔT (delta temperature) is the design indoor temp minus the design outdoor low. Standard US design temps: 70°F inside, climate-zone-dependent low (-10°F to 30°F). For whole-home systems, use a Manual J calculation.
Frequently asked
What ΔT should I use?+
Indoor: 70°F. Outdoor "design temp": 99% winter — see ASHRAE tables. Atlanta: 22°F → ΔT 48. Chicago: -2°F → ΔT 72. Minneapolis: -16°F → ΔT 86.
Old vs new construction?+
Old (poor): 5 BTU/ft²/°F. Modern: 3 BTU/ft²/°F. New construction with R-30 walls: 2 BTU/ft²/°F.
Does this match my furnace size?+
Often furnaces are oversized. A 100,000 BTU furnace covers a typical 1,500 ft² home in moderate climate.
Heat-pump vs furnace?+
Same BTU output measure. Heat pumps lose efficiency below freezing — verify Cold-Climate spec.
Why include insulation?+
A drafty wall lets heat escape — you need more heating to compensate. Insulation halves the load roughly.
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