The circulation fan in an air conditioner can be a valuable energy saver in certain climates at certain times of day. Those are important caveats, because an air conditioning fan can also increase energy costs if not used properly.
The U.S. Department of Energy Office of Energy Efficiency and Renewable Energy recommends buying a central air conditioner with a fan-only switch, but only recommends using the fan-only setting when the temperature drops at night.
Use a circulation fan to circulate outside cool air into a home instead of running the compressor, particularly in dry, mild climates. Experts at the Energy Extension Service at Kansas State University estimate that the compressor uses 10 times as much energy as the fan in a central air conditioner. Therefore, the fan can keep the house cool, pull in more fresh air and save money on energy bills.
This only works when the temperature drops substantially at night. Of course, every person has a different idea of comfort, but circulation fans may be a good bet when the outside temperature is below 85.
On the other hand, during the day and on evenings during heat waves that don’t bring nighttime relief, a fan may increase energy usage. This is because the fan will make the compressor work harder to dehumidify the air. The air conditioner draws out moisture, which collects on the coils. When the fan is run without the compressor, this moisture may evaporate again, forcing the compressor to work harder when it cycles on again.
Set the fan to the “auto” position whenever the compressor is running, and the outside air is too hot.
For air circulation, it’s better to rely on ceiling fans in individual rooms while they are occupied. Ceiling fans offer comfort, but do not actually reduce the temperature, so even though they are energy misers, there is no sense in running them in an empty room.
Another option is a whole-house fan, which is something of a hybrid between an attic fan and a ceiling fan. Whole-house fans typically go into the ceiling in a central part of the house. They are designed to draw in cool air and exhaust hot air. They use about one quarter of the electricity of a central air conditioning system, but they are also only effective during relatively cool periods. Experts suggest whole-house fans are most effective when the exterior temperatures are below 82 degrees.
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