The blades on a ceiling fan are set at an angle so that they can push air more effectively as they rotate. Fans typically include switches that vary the speed the blades turn: low, medium or high. In summer or on warm days with high humidity, fans need to run at a medium or high speed to achieve the best cooling effect. Fan size also determines the proper cooling for the room. If the room's longest wall is 12 feet or less, a 36-inch diameter fan will keep occupants feeling cool. Rooms with walls of 12 to 15 feet need a 42-inch fan and rooms 15- to 18-feet long should be equipped with a 52-inch fan.
Wind Chill Effect
While the room's actual temperature will not change on humid days, the breeze ceiling fans stir make the room seem that way. The breeze creates a wind chill effect that evaporates moisture from skin. Consequently, people feel cooler. "Just the air movement in the room alone can make it feel cooler by four degrees or more," the California Energy Commission claims.
Most ceiling fans have a switch that controls the direction the blades rotate. In summer, to achieve the wind-chill effect, blades must turn in a counterclockwise rotation. When set correctly at the proper rotation and fan speed, a cool breeze is evident when standing directly below the fan. Air continues to move and circulate throughout the room, but the strongest wind chill is apparent from the downdraft caused by the ceiling fan.
Running Fans Continuously
Since the room's temperature is not lowered by ceiling fans, the units should be turned off when people are not occupying the space. Running fans continuously when people are not present wastes electricity and may raise temperatures slightly as the heat from fan motors permeate the room.