Attic Fans displace hot air that rises from your home into your attic and replaces it with cooler air that is drawn from vents or windows below the attic. In most cases, a whole-house fan is mounted in the attic floor, above a rectangular grille in the ceiling of a central hallway. Once the outdoor temperature cools down â€“ usually in the evening or early morning â€“ the homeowner opens a few downstairs windows, closes the fireplace damper, and turns on the fan. (The wall switch that controls a whole-house fan should be properly labeled so that it isnâ€™t accidentally turned on during the winter.) Once the house has cooled off, the fan can be turned off and the windows closed.