Centrifugal fan

A fan includes a fan housing located on an axis. The apparatus has axially front and rear sections that together define a chamber. Air can enter the chamber through an inlet in the front section. An impeller in the chamber is configured to rotate about the axis to drive the air radially outward. A trough-shaped channel in the rear section extends circumferentially about the axis from a first end of the channel to a second end of the channel. The channel is configured to channel the air away from the first end circumferentially toward the second end. The axially extending depth of the channel increases from the first end toward the second end such that, over a 90° range, an increase in the depth is more than twice an increase in the radially extending width of the channel.