During hot weather, you’re likely to use electric fans, especially if you don’t have air conditioning. Fans work by moving air over your skin so your sweat evaporates faster, which has a cooling effect. You may be surprised to know, though, that they don’t help in all situations—and some researchers contend that they sometimes do more harm than good.
How well do fans cool?
- Fans can provide some comfort in the heat, but only if they circulate cooler air, not air that is near or above body temperature (mid-to-upper 90s or higher). Otherwise they may contribute to heat gain, because the fan is moving heat toward the body.
- Unlike air conditioning, fans do not cool the room or remove humidity. Moreover, they are less effective when used in a very humid environment, because high humidity makes it difficult for sweat to evaporate.
- How effective fans are also depends on your physiology—for instance, how much you sweat—and other factors. In older people, the ability to sweat is typically reduced, which makes them less able to remove heat from the body. Chronic illness, poor circulation and the use of some medications (such as beta blockers) can also reduce the body’s ability to sweat and adjust to heat. In such cases, spraying a little water on the skin while using a fan may help.
- A 2012 review by a team of international researchers could not come to any conclusions regarding the use of fans during heat waves because of the lack of good studies. Some studies have linked fans to reduced heat stroke and mortality during heat waves, but others have linked them to worse health outcomes. According to the Centers for Disease Control and Prevention (CDC), fans won’t prevent heat-related illness when the temperature is in the high 90s or above.
Fans versus air conditioners
- Compared with air conditioning, fans can save energy and money. Except on the hottest days, you may be able to use them in place of air conditioning. And using them with air conditioning will allow you to set your air conditioner thermostat higher.
- Keeping your windows open when you use a fan helps reduce indoor air pollutants, which accumulate when you seal up your house to use air conditioning.
- Ceiling fans, in particular, can be cost-effective. Ones with larger blades move more air than ones with smaller blades, at the same speed—but factors to consider when choosing a ceiling fan include the size and layout of the room, the ceiling height and where it will be positioned.
- A whole-house fan system ventilates your entire home at a fraction of the cost of air conditioning. Best used at night and in the early morning, in combination with ceiling and portable fans, it draws cooler air in from open windows and expels hot indoor air through attic vents.
- Twin (also called double) window fans can be set to draw in cooler air from the outside or to blow out hot interior air. They work best when blowing in air from outside. If there is a good seal between the fan and the window, they can be somewhat effective in the exhaust mode. In general, it’s harder to get a fan to efficiently exhaust air than to blow air in.
How to beat the heat
Whether you use air conditioning, fans or some combination, it’s important to drink plenty of water and other nonalcoholic fluids in hot weather. To reduce the risk of heat-related illness, if you don’t have air conditioning at home and it’s very hot, seek out air-conditioned spaces, such as shopping malls, restaurants, the local library or a movie theater, even if for just a few hours. During heat waves, your local community may open cooling centers.