Abstract: A clean room fan unit is used to provide a continuous flow of air to a clean room, where the air flow is substantially free of undesired impurities. The fan unit includes a rectangular housing that defines a cavity. A fan unit is located inside the cavity for drawing air into the housing and into the clean room. The fan has blades with pitch angles selected to provide a particular flow path and flow rate that reduces the amount of noise generated by the fan unit while increasing the efficiency of the fan unit. A perforated plate is situated within the air flow path in the fan unit housing such that the perforations diffuse the air flow before it passes through a filter and exits the housing. The uniform air flow provided by the perforated plate produces a reduced noise level.