HVAC
HVAC BTU Calculator
Estimate the BTU capacity a room needs for cooling, adjusted for ceiling height, sun and occupancy.
Result
This is a preliminary sizing estimate using industry rules of thumb. Actual equipment selection requires a room-by-room load calculation (ACCA Manual J) and duct design (Manual D) by a qualified professional, oversized equipment short-cycles, dehumidifies poorly and fails early.
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About this calculator
How many BTU do I need per square foot?
Around 20 BTU per square foot is the common starting point for cooling in a moderate climate. Insulation, window area, orientation and air sealing move that figure substantially in either direction.
What happens if the unit is too big?
It cools the air quickly, shuts off before removing humidity, and short-cycles. The room feels cold and clammy, and the compressor wears out early. Oversizing is a more common fault than undersizing.
Is this a Manual J calculation?
No. This is a rule-of-thumb estimate for early conversations. Manual J models each room's construction, windows, orientation and infiltration, and is what equipment should actually be selected on.
The formula
base BTU = area × 20, then adjusted for ceiling height, sun, occupants and room type
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