Abstract: An exhaust fan unit (26) is mounted in a hole (86) which extends through a central region (27) of a lid (22) of a water closet (12) for exhausting air from within a bowl (16) of the water closet (12) when the lid (22) is horizontally disposed, in a closed position. A housing (32) is mounted to the lid (22) and has a window (56) for receiving a filter cartridge (34). A control circuit (96) has a position sensor (144) and control logic (142). The position sensor (144) detects when the lid (22) is moved from a vertically disposed, open position to the closed position. The control logic (142) applies electric power to operate the fan unit (72) for a predetermined time interval when the lid (22) is disposed in the closed position.