The main difference between indoor and outdoor ceiling fans comes down to moisture. Indoor ceiling fans (dry-rated) are designed to service indoor areas that aren’t exposed to moisture. Outdoor ceiling fans are in either one of two categories: wet-rated or damp-rated. Wet-rated indoor/outdoor ceiling fans are built to withstand the elements and can rain be installed indoors or outdoors. Damp-rated outdoor fans can be installed in covered, damp areas but are not meant to be exposed to the elements.