Only if the box is UL-listed for fans (marked "Fan Rated"). Otherwise, replace it with a braced ceiling fan box screwed to a joist.

Remove the cover, vacuum dust, wipe blades with soapy water, and clear exterior vent flaps.

Use rigid or flexible ductwork to direct moisture outside (never into an attic or wall). Install a roof or wall vent cap and ensure the duct is as short and straight as possible to prevent condensation buildup.