A bathroom exhaust fan sucks air out of the bathroom and directs it outside. It creates air circulation in the space, with replacement air usually coming through the door or an open window.

Do ductless bathroom fans work as well? No. Ductless fans pull air through a system of filters and release it back into the room. They can purify the air, but don't remove moisture.

More important, if you have a smaller bathroom (around 50 square feet or smaller), that smaller duct size—and the fans built for it—may work quite effectively for you anyway.