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Calculate heating and cooling BTU needs by room size, insulation, and windows.
A BTU calculator estimates the British Thermal Units needed to heat or cool a room based on its size, insulation, ceiling height, and window count.
| Room Size | Cooling BTU | Heating BTU |
|---|---|---|
| 150 sq ft | 5,000 | 4,000–5,000 |
| 300 sq ft | 7,000 | 7,000–8,000 |
| 450 sq ft | 10,000 | 10,000–12,000 |
| 700 sq ft | 14,000 | 14,000–18,000 |
| 1,000 sq ft | 18,000 | 20,000–25,000 |
| 1,500 sq ft | 24,000 | 30,000–40,000 |
Formula
BTU = Room Area × BTU per Sq Ft × Insulation Factor + Window BTURoom Area = length × width in square feet
BTU per Sq Ft = 20 for cooling, 25–30 for heating
Insulation Factor = 0.85 (good), 1.0 (average), 1.3 (poor)
Window BTU = ~1,000 BTU per window for cooling
Worked Example
300 sq ft room, average insulation, 3 windows (cooling)
Did you know? The U.S. Department of Energy estimates that heating and cooling account for about 48% of the energy use in a typical U.S. home (source: DOE).
Sources
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