A duct for a vehicle includes an inlet fluidly coupled to an interior of the vehicle and an outlet fluidly coupled to the inlet. A buoyant closure member is disposed between the inlet and the outlet and is movable between an open position permitting flow between the inlet and the outlet and a closed position preventing flow between the inlet and the outlet. The buoyant closure member is normally in the open position and is movable from the open position to the closed position in response to a predetermined volume of water entering the outlet.