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About the BTU Calculator
The BTU Calculator estimates the heating and cooling capacity a room needs, measured in British Thermal Units per hour. Enter your room dimensions and conditions, and it returns a recommended BTU rating for your heater or air conditioner.
The calculation uses the common rule of thumb of roughly 20 BTU per square foot of floor area. It then adjusts that base figure for ceiling height, insulation quality, sun exposure, climate, and the number of occupants. You need the room's length and width, plus a few details about its conditions. Measure the room carefully before you start, because small errors in the dimensions shift the final result.
- Measure the room's length, width, and ceiling height.
- Select insulation, sunlight, climate, and occupancy details.
- Read the BTU result and match it to a heater or air conditioner.