Various ceiling fans are used in both summer and winter. Warm air rises. The blades or direction of many fans can be changed so that air is encouraged to rise up and out or down and into the room.
In summer, the fan's rotation direction is set so that it blows air upward. This helps the warm air rise and pulls it away from the people in the room. The movement of the air also cools people more quickly.
In the winter, when many buildings are heated (in colder climates), the fan is used to push warm air downward along the walls, which forces the warm air that originally rose to be pushed to the lower levels of the room.
- Bob Vila's blog on Winter Ceiling Fans