For heating, ceiling fans should usually be set to blow the air upward. Air naturally stratifies, i.e. warmer air rises to the ceiling while cooler air sinks, meaning that colder air settles near the floor where people spend most of their time. A ceiling fan, with its direction of rotation set so that air is drawn upward, pulls the colder air off the floor, forcing the warmer air nearer the ceiling to move down to take its place, without blowing a stream of air directly at the occupants of the room. This action works to even out the temperature in the room, making it cooler nearer the ceiling, but warmer nearer the floor. Thus the thermostat in the area can be set a few degrees lower to save energy while maintaining the same level of comfort. However, downdraft would usually do better job at circulating the room, so if fan can spin slow enough to not cool people, it can be left on downdraft in winter. In fact, Emerson sold fans with the name "Heat Fan" which were made to push heat down in winter when they figured how ceiling fans can be useful in winter, and they are downdraft only.