Abstract: An improved centrifugal fan whose air capacity is to be increased, without changing the dimensions of the casing and without using a higher-powered motor improves the fan by a) reducing the volume of the pressure space by enlarging the impeller diameter, b) shifting a location of a least distance between the impeller and the casing in the direction of rotation of the impeller, c) forming a wedge-shaped space ahead of the location of the least distance, and d) providing the impeller with very flat blades. The centrifugal fan has a higher air capacity at a lower rpm.