Abstract: An exhaust fan has an annular exhaust duct, a fan wheel, and a drive motor inside the core of the exhaust duct, and not inside the annular passage for the exhaust fluid. The exhaust duct has a tubular window frame extending between the inner and outer walls of the exhaust duct and creating service windows for a worker to reach in an de-couple the driver motor from both a bracket for its mount and also from the fan wheel. Temporary locking mechanisms actuated from reaching through the service windows removably hold the fan wheel to the exhaust duct while the drive motor is de-coupled and removed. The exhaust fan further includes self-centering mechanical connections between the drive motor and fan wheel so that the fan wheel does not have to be removed to be re-balanced.