A British Thermal Unit (BTU) measures heat energy. One BTU equals the energy needed to raise the temperature of one pound of water by 1°F.
Common Uses
- HVAC: AC units rated by BTU/hour (e.g., 12,000 BTU = 1 ton of cooling)
- Heating: Furnace output measured in BTUs
- Energy content: Natural gas ≈ 1,030 BTU per cubic foot
Rough Sizing Guide (AC)
- 150–250 sq ft: 6,000 BTU
- 250–350 sq ft: 8,000 BTU
- 350–550 sq ft: 12,000 BTU
- 550–700 sq ft: 14,000 BTU
Conversions
1 BTU = 1,055 joules. 1 kWh = 3,412 BTU. 1 therm = 100,000 BTU.