BTU to CFM Calculator

Estimate airflow required to move a given heat load at a known temperature difference.

Calculator

Heat Load (BTU/hr)

Temperature Difference (ΔT °F)

Calculated Airflow

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Enter values above and click calculate.

How It Works

This calculator uses the standard sensible heat formula to determine how much airflow is needed to move a given heat load across a temperature difference. It's commonly used when sizing supply air, checking equipment capacity, or estimating register airflow.

CFM = BTU/hr ÷ (1.08 × ΔT)

Where:
BTU/hr = the heat load to be moved in British Thermal Units per hour
1.08 = a fixed air constant - air has a known density and specific heat, and when combined they produce this value. It only changes at extreme altitudes or temperatures.
ΔT = the temperature difference between supply and return air in °F
CFM = the required airflow in cubic feet per minute

Typical ΔT values used in the field:
Cooling systems: 15–20°F
Heating systems: 20–30°F
High efficiency systems: 10–15°F

Common example: A 24,000 BTU/hr load with a 20°F ΔT requires approximately 1,111 CFM of airflow.