BTU Calculator
Estimate room-air-conditioner cooling with the ENERGY STAR size chart, or explore heating heat loss from walls, windows and air exchange.
Estimated capacity
Estimated capacity
—The kW result is thermal capacity, not electrical input. Power consumption depends on equipment efficiency, COP or EER.
Calculation breakdown
Nearby reference sizes
Nearby listed capacities are reference points, not purchase advice. Oversized cooling equipment can short-cycle and control humidity poorly; check the manufacturer's guidance and professional load calculation.
The cooling chart assumes an 8-ft ceiling. Taller rooms may need more capacity; no arbitrary multiplier has been added.
Method and limitations
Cooling follows the ENERGY STAR room-AC chart for 100–2,500 ft². Shade changes the baseline by −10%, strong sun by +10%; each person above two adds 600 BTU/h and kitchen use adds 4,000 BTU/h. These are chart adjustments, not a complete building load calculation.
Heating is a simplified steady-state estimate: heat loss through exposed surfaces plus air exchange. It uses assumed U-values and air-change rates, not a measured survey or a Manual J load calculation. Exterior-wall area is approximated from the wall count.
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