Fan Affinity Laws
Flow:CFM2 = CFM1 × (RPM2 / RPM1)
Pressure:SP2 = SP1 × (RPM2 / RPM1)²
Power:BHP2 = BHP1 × (RPM2 / RPM1)³
Target RPM:RPM2 = RPM1 × (CFM_target / CFM1)
Original Fan Conditions
Speed Change — Enter New RPM
—
Or — Solve for Target CFM → Required RPM
—
Results — New Fan Conditions
New CFM
—
CFM
New Static Pressure
—
in wg
New BHP
—
BHP
New kW Input
—
kW
Speed vs. Performance Table
| RPM | Speed % | CFM | SP (in wg) | BHP | kW Input | Power vs. Full |
|---|
Fan affinity laws assume the fan operates on the same system curve (duct resistance proportional to flow²). Actual performance may differ due to VFD slip, motor saturation, or system curve changes.