The speed of an extractor fan motor is set by the fan impeller, not by you: the motor must match the speed the impeller was designed for. If the impeller sits directly on the motor shaft, keep the speed on the old nameplate (about 1,450 or 2,900 rpm); on a belt-driven fan, consider it together with the pulley ratio.

Why is changing the speed risky?

In fans the power demand grows with the cube of speed. Running the same impeller at 3,000 instead of 1,500 rpm theoretically needs eight times the power; the motor is overloaded, and the hub and blades may not be designed for that speed. Conversely, fitting an impeller built for 3,000 rpm to a 1,500 rpm motor clearly reduces air volume and pressure, and the hood or duct suction becomes insufficient.

What to check when choosing

  • The kW, speed and voltage on the old motor's nameplate
  • Whether the impeller is on the shaft or on a pulley; shaft diameter and key size
  • Mounting: foot (B3), flange (B5/B14) or the vertical positions common on roof units (such as V1, V3)
  • Noise expectations: for the same airflow, a larger impeller at lower speed usually runs more quietly; the fan maker's data decides this
  • If airflow needs adjusting, a frequency inverter; our three-phase series are suitable for speed control

We explain how the number of poles affects torque and frame size in the question on choosing a 2, 4 or 6-pole motor of the same power. For roof-mounted fans, also see the roof exhaust fan motor page.

HEM Motor ships IP55, class F insulated three-phase motors in 1,500 and 3,000 rpm versions from stock in İzmir/Buca. Before choosing from the industrial fan motors, send a photo of the old motor's nameplate and of how the impeller is attached via WhatsApp; we will identify the equivalent model together.