Paddle Blade (Radial blade)

Simple and robust, good for conveying dusts, self-cleaning, bulky, not very efficient - 45%

Forward Curve (Multi-Vane)

High outlet velocity and good volume, fairly quiet, general ventilation duties, quite efficient - 70%. Sizes 75mm to 1.8m maximum pressure about 750 Pa.

Backward Curve

Can have aerofoil blades, high speed and pressures, non-overloading, high efficiency - 85% Sizes 38mm (15") to 3.6m (12') max. pressure about 1500 Pa for average ventilation jobs. Much higher for "specials".