Work out fan laws instantly with clear inputs, formula shown and shareable results.
The fan laws state that for a fixed system, airflow varies with speed, pressure with the square of speed and power with the cube of speed. The cube relationship is why trimming a fan by 20 percent saves nearly half its energy, and why speeding one up by 20 percent nearly doubles the motor load.
Fan laws
CFM2 = CFM1 x (N2/N1); SP2 = SP1 x (N2/N1)²; P2 = P1 x (N2/N1)³
CFM2 = CFM1 x (N2/N1); SP2 = SP1 x (N2/N1)²; P2 = P1 x (N2/N1)³. The fan laws state that for a fixed system, airflow varies with speed, pressure with the square of speed and power with the cube of speed.
No. They apply only when the system curve is unchanged. Adding dampers or duct alters the resistance and moves the operating point off the original curve.
This calculator takes 4 inputs: Original fan speed, New fan speed, Original airflow, Original static pressure. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.