• Ceiling Fans

  • A ceiling fan rotates much more slowly than an electric desk fan; it cools people effectively by introducing slow movement into the otherwise still, hot air of a room. Fans never actually cool air, unlike air-conditioning equipment, but use significantly less power (cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency.

    Unlike air conditioners, fans only move air—they do not directly change its temperature. Therefore, ceiling fans that have a mechanism for reversing the direction in which the blades push air (most commonly an electrical switch on the unit's switch housing, motor housing, or lower canopy) can help in both heating and cooling.

    Some ceiling fans are mechanically reversible (have adjustable blade pitch) instead of an electrically-reversible motor. In this case, the blade should be pitched to the right (or left if the motor spins clockwise) for downdraft, and left (or right if the motor spins clockwise) for updraft. 

    In summer, the fan's direction of rotation should be set so that air is blown downward (Usually counter-clockwise from beneath). The blades should lead with the upturned side as they spin. The breeze created by a ceiling fan speeds the evaporation of perspiration on human skin, which makes the body's natural cooling mechanism much more efficient. Since the fan works directly on the body, rather than by changing the temperature of the air, during the summer it is a waste of electricity to leave a ceiling fan on when no one is in a room.

    In winter, ceiling fans should be set to turn the opposite direction (usually clockwise; the blades should spin with the downward turned side leading) and on a low speed (or the lowest speed the fan is able to circulate the air down to the floor). Air naturally stratifies—that is, warmer air rises to the ceiling while cooler air sinks. Unfortunately, this means it is colder on or near the floor where human beings spend most of their time. A ceiling fan, with its direction of rotation set so that air is drawn upward, pulls up the colder air below, 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. It is important to run the fan at a low speed (or a lowest speed the fan is able to circulate the air down to the floor) to minimize the wind chill effect described above.

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