It is a fan in which air flows in a radial or perpendicular direction directly relative to the fan shaft . It also included the fan wheel, wheel, fan housing, drive mechanism, and inlet or outlet dampers. The fan wheel consists of fan blades mounted on a hub, which is turned on a shaft that passes through the fan housing. Air enters the fan through the center of the fan wheel, then turns 90 to pass over the fan blades and exit the fan housing. -forward or backward curved blowers, lld fan, i.dfd fans