Abstract: A centrifugal fan system for a building, including a centrifugal fan mounted for rotation about a vertical axis and having a bottom inlet. The fan is mounted in a movable housing having a fan chamber and an air outlet arranged in a side thereof. Wheels are mounted on both sides of the fan housing and engage two elongate track members, that extend horizontally and are mounted on a suitable supporting structure. Thus, the fan and its housing can be moved horizontally away from the top of an input flow concentrator. The housing has an internal, perforated scroll-shaped wall and vertical external walls. Sound insulation is located between the scroll-wall and the external walls. An electrical motor is mounted on the side of the housing and is connected to drive the fan.