Panasonic VF1 WhisperFit ventilation fans are not only as energy efficient as conventional panasonic Ceiling fans, but they are compatible with either 3 or 4 inch duct and are only 5.5 inches deep. Note that they are not quite as quiet as their larger Panasonic counterparts, but nearly so. As with other Panasonic fans these fans are rated for continuous operation, include a built in backdraft damper, thermal fuse protection, and rust proof paint on a galvanized steel body.