← HVAC Systems Studio
💨

Fan Sizing Calculator

CFM · Static Pressure · BHP · Motor kW · ASHRAE 90.1

When to use: Use to select a fan and motor for air handling units (AHU), exhaust fans, and supply fans. Enter the design airflow (CFM) and total static pressure (TSP) from your duct sizing calculations (ACCA Manual D). The calculator determines brake horsepower (BHP), motor size, kW draw, and fan efficacy (W/CFM) for ASHRAE 90.1 compliance. Apply an altitude correction for sites above 1,000 ft elevation.

Fan Parameters
CFM
0.5–3.0 typical
in. w.g.
0 = sea level
ft
Motor BHP Required
1.54
BHP at Motor Shaft
Select: 2 HP motor
Performance Summary
Altitude Correction Factor1.000
Corrected CFM at Altitude5,000 CFM
Air Power (theoretical)1.439 HP
Motor BHP (with fan & motor eff.)1.54 BHP
Motor Power Draw1.15 kW
Fan Efficacy0.230 W/CFM
Selected Motor Size2 HP (next std. size)
References
ASHRAE 90.1 – Fan power limitation (W/CFM)
HP = CFM × TSP / (6356 × Fan Eff.)
Motor size = next standard HP above 1.15 × BHP
Altitude: air density ∝ (1 − 2.26e-5 × alt)^5.26