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BTU/hr
kW
CFM
L/s
Area (sq.in.)
Area (cm²)
RA DB (°F)
RA DB (°C)
SA DB (°F)
SA DB (°C)
RA WB (°F)
RA WB (°C)
ΔT (°F)
ΔT (°C)
SP (in. w.c.)
SP (Pa)
TP (in. w.c.)
TP (Pa)
VP (in. w.c.)
VP (Pa)
FPM
m/s
Dew (°F)
Dew (°C)
SA RH (%)
RA RH (%)
What to calculate
Original RPM
New RPM
Original CFM
Original SP (in. w.c.)
Original BHP (optional)
Fan Law 1: CFM₂ = CFM₁ × (RPM₂ / RPM₁) Fan Law 2: SP₂ = SP₁ × (RPM₂ / RPM₁)² Fan Law 3: BHP₂ = BHP₁ × (RPM₂ / RPM₁)³ Assumes constant system resistance and air density.