BTU Calculator
Estimate the BTU heating/cooling capacity needed for a room.
Sizing a heater or air conditioner for a room means estimating the BTU (British Thermal Unit) capacity needed — too small and it won't keep up; too large and it wastes energy cycling on and off.
Why room type changes the calculation
Kitchens and sunrooms generate or receive more heat than bedrooms, which is why this calculator uses a different BTU-per-square-foot factor depending on room type — an accurately sized unit runs more efficiently and maintains more consistent comfort than an oversized or undersized one.
Frequently asked questions
Is bigger always better for heating/cooling capacity?
No — an oversized unit cycles on and off more frequently, which is less energy-efficient and can leave a room feeling clammy (for AC) since it doesn't run long enough to properly dehumidify.
Does ceiling height affect the BTU calculation?
Yes — a taller ceiling means more total air volume to heat or cool, though this calculator's simplified estimate primarily uses floor area as the main factor.