HVAC BTU Calculator
Get a quick estimate of the cooling BTUs and tonnage a space needs based on its size, sun exposure, and occupants — handy for fast sizing conversations with customers.
Estimate only, based on a ~20 BTU/sq ft rule of thumb with simple adjustments. For an accurate system size, a professional should perform a Manual J load calculation that accounts for insulation, windows, climate, and ductwork.
How HVAC BTU sizing works
BTU (British Thermal Units) measures heating and cooling capacity. For cooling, a common starting point is roughly 20 BTU per square foot, then adjusting for sun exposure, ceiling height, insulation, and the number of people who use the space. Air conditioner capacity is often expressed in tons, where one ton equals 12,000 BTU per hour.
This tool gives a fast estimate, but proper sizing should always be confirmed with a Manual J load calculation. Oversized systems short-cycle and struggle with humidity; undersized systems run constantly and wear out early.
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