Duct fan is a fan that is installed inside of a ventilation duct, rather than at the end point of a duct or through a wall. Fans are mechanical units designed for air transportation in the ducts, direct air supply or air exhaust from the premises. Air is moved due to the pressure drop between the fan inlet and outlet vent.

An axial fan has the form a cylindrical-cased wheel with the impeller fixed to a bushing at some angle to rotation plane. As the impeller blades rotate air is trapped betwen and is moved further axially. Air is hardly moved in the radial direction. The axial fan blades are mostly set directly on the motor shaft.

Round inline fans are available in standard sizes ranging from 100 up to 450 mm with the air capacity range from 200 to 5250 m3/h. The impellers with backwardcurved blades are powered by the asynchronous external rotor motors. The ball bearings are rated for long service life.