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CFM Airflow Calculator

Supply Airflow · ASHRAE 62.1 OA · BTU/hr to CFM

When to use: Use to determine the required supply airflow (CFM) for a zone based on its cooling or heating load. The formula CFM = BTU/hr ÷ (1.08 × ΔT) converts load to airflow, where ΔT is the temperature difference between supply air and room setpoint (typically 15–25°F). Also calculates the minimum outdoor air required per ASHRAE 62.1 based on occupancy and floor area.

Zone Parameters

Zone Cooling/Heating Load

BTU/hr

Supply Air Temperature Differential (ΔT)Cooling: 15–25°F

°F

Floor Area

ft²

Design Occupancy

people

Space Type (ASHRAE 62.1)

Required Supply Airflow

1,667

CFM

Results

Supply Airflow (load-based)1,667 CFM

Min. Outdoor Air (ASHRAE 62.1)80 CFM

Equivalent Cooling Load3.0 tons

CFM per Ton556 CFM/ton

Temperature Differential20 °F

References

CFM = BTU/hr ÷ (1.08 × ΔT)

ASHRAE 62.1 Table 6-1 – Ventilation rates

Typical: 350–450 CFM/ton for cooling

Supply air temp: 55°F cooling, 105–120°F heating