When it's the middle of winter and freezing outside, it's probably safe to say that most of us aren't thinking about our ceiling fans. However, running fans in the colder months can actually save up to 10% on heating costs and is as simple as flipping a switch.
In the summer months, the slightly angled blades of a ceiling fan turn counterclockwise to move air down, making people feel cooler due to a concept known as the wind chill effect. During winter, the warm air generated by your heating system naturally rises to the ceiling while cooler air sinks. By switching the direction that your fan blades turn, that cooler air is drawn upwards, which forces the warmer air near the ceiling back down into the space.
How does this save energy? Since thermostats are typically located at human level, keeping the warm air low where it's needed means you can turn the temperature down a few notches and still stay warm.
On most fan models, there is generally a small switch on the fan to reverse the direction (I actually had to remove a few screws to reach ours). Additionally, running the fan at the lowest speed will circulate air while reducing the feeling of actual air movement in the room. While this technique should work in standard size rooms, it works especially well in vaulted or tall ceiling spaces where the people occupying the space are further separated from the warm air collecting at the ceiling. Furthermore, even though running a fan uses a small amount of electricity, there is generally still a net savings in energy use.
Just remember, clockwise in winter, counterclockwise in summer.
Re-edited from a post originally published 2.09.11 - CM