A centrifugal fan is formed from an impeller installed within a casing. The impeller is formed from two plates that are interconnected by a plurality of blades. A duct extends through each blade. At each of its ends, the duct opens at one of the plates. Air enters the fan from through a central opening formed in one of the plates, moves to a medial zone between the plates, and exits the fan at the medial zone's unwalled periphery. Air also crosses the fan by way of the ducts formed within each blade.