Free HVAC BTU calculator

What BTU output do I need?

Rough sizing for room or whole-home heating and cooling. Plug in the conditions, get the BTU output range to match against equipment. This is a planning tool — full Manual J load calcs are still needed for permit and final spec.

Square footage to condition

Climate zone

Cold zones need bigger heating, hot zones need bigger cooling.

Insulation quality

Ceiling height (ft)

Standard 8'. Cathedral / open ceilings increase load.

Number of regular occupants

Each person adds ~600 BTU/hr of cooling load.

Sun exposure

BTU output recommended

Cooling

BTU/hr (≈ 0 tons)

Heating

BTU/hr

Volume conditioned: 0 cu ft
Cooling per sq ft: 0 BTU
Heating per sq ft: 0 BTU

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About this calculator

This tool gives a quick BTU range based on common rule-of-thumb factors: square footage, climate zone, insulation, ceiling height, occupants, and sun exposure. For permit-ready sizing or rebate qualification, run a full Manual J or CSA F280-12 calculation.

Cooling guidance: 20-25 BTU/sq ft in hot climates, 15-20 in mixed, 12-18 in cold-climate Canadian markets (where cooling is short-season). Heating guidance: 30-50 BTU/sq ft in cold climates, 25-40 in mixed, 15-25 in hot climates.