It has been known to the air moving industry for some time that duct fittings installed close to a fan’s inlet or outlet have adverse effects on the fan’s performance. The magnitude of these adverse effects is generally determined through laboratory testing, and the body of knowledge is relatively small compared to the possible number of combinations of fan types, duct and inlet configurations, and duct fittings.

The purpose of this research project was to determine the effect of a limited number of various inlet installations and product configurations on the air performance and sound of a typical forward curved centrifugal fan.