When I was a young backpacker traveling through India, Sri Lanka, and Thailand in the 1970s, I couldn’t afford air-conditioned hotels or restaurants. In these tropical conditions, I became quite accustomed to the benefits of Casablanca-style fans.
Although a fan can’t lower the temperature of the air, it can make people feel cooler. Moving air accelerates the rate at which perspiration evaporates from your skin. The evaporation process requires heat, so increased evaporation means that more heat is leaving your body.
Moving air also removes heat from your body by convection — at least as long as the air temperature is below 100°F or so. Once the air temperature significantly exceeds your body temperature, however, fans tend to raise rather than reduce your body temperature (unless you are very wet).
Fans use electricity and their motors give off heat, so it’s important to use them sparingly and appropriately.
Ceiling fan energy use varies by model. Watt draw ranges from 15 to 30 watts on low speed, 30 to 50 watts on medium speed, and 50 to 100 watts on high speed. According to a paper by Danny Parker, Michael Callahan, Jeffrey Sonne, and Guan Su, the average Florida home has 4.3 ceiling fans and consumes about 800 kWh per year to operate these fans.
A central air conditioner requires far more power — on the order of 2,000 to 5,000 watts.
Alas, many people never turn off their ceiling fans. Even in homes with six or seven fans, the fans are often left humming for 24 hours a day.
But a fan in an empty room isn’t cooling the chairs or beds; rather, its motor is giving off heat. Seven 60-watt fans give off 420 watts continuously. In 24 hours, the waste heat from these fan motors is equivalent to ten hours’ operation of a 1,000-watt hair dryer.
Ceiling fans were…