A centrifugal fan should spin in the direction specified by the manufacturer, usually marked by an arrow on the housing or motor. Correct rotation ensures that the impeller blades scoop air properly and push it into the scroll housing, delivering the airflow and pressure the fan was designed for.
Most centrifugal fans are available in clockwise (CW) or counter-clockwise (CCW) rotation when viewed from the drive side or from the inlet side. The rotation direction is selected during design to suit the layout of the ductwork and the required outlet orientation. The fan nameplate, drawing or catalogue sheet will specify both the rotation (CW or CCW) and the discharge position (such as 90°, 180° or 270°).
If the fan spins in the wrong direction, it will still move some air, but performance will be drastically reduced. The blades will not capture and accelerate the air as intended, and the scroll housing will not convert velocity to pressure efficiently. The fan may deliver only a small fraction of the rated airflow and pressure, and it may generate excessive noise or vibration. In mining or critical industrial ventilation, this can lead to unsafe under-ventilation.
To check the rotation direction safely, technicians briefly “jog” the motor while observing the shaft or fan wheel through an inspection opening or viewing window, with all guards and safety procedures in place. The observed direction is then compared with the arrow cast or stamped on the housing. For three-phase motors, reversing any two supply phases will reverse the rotation. For single-phase motors and some special drives, different wiring or parameter changes are needed.
It is also important to align the rotation with the impeller blade orientation. Radial blades are symmetrical and less sensitive to rotation direction, but backward-curved and forward-curved blades are designed to work optimally in a specific rotational sense. Running them backwards can overload the motor or create unstable flow.
In summary, a centrifugal fan must spin in the rotation direction indicated by the manufacturer’s arrow and documentation. Correct rotation is essential for achieving the specified airflow and pressure and for safe, efficient operation in industrial and mining ventilation systems.
