This summer’s first extreme heat wave in North America—the result of a heat dome that has settled over the U.S. Midwest and Northeast—is causing tens of millions of people to swelter in record-breaking temperatures and humidity.
As the heat soars, more air conditioners will be switched on. But it’s important to use air-conditioning effectively. And for those who lack it—or who want to minimize their bill and strain on the power grid—there are other ways to help keep a home relatively cool. Scientific American spoke with experts to learn some tips for keeping cool. Many of these measures are small and inexpensive, making them widely accessible. “These little changes don’t have to cost you a lot of money,” says Jami Seymore, a spokesperson at Energy Trust of Oregon, a nonprofit focused on energy savings and clean energy.
Personal Needs
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To begin with, “different people have different temperature needs,” says Mark Kear, an assistant professor at the University of Arizona’s School of Geography, Development & Environment. Certain medical conditions or medications can impair the body’s ability to regulate its temperatures, for example, so affected people may need more cooling than others. Likewise, very young children and older people are often more susceptible to heat. And some people are more acclimated to extreme climates than others; what is stifling to someone in Minneapolis may be normal to someone in Miami. So being aware of the needs of those in your household is important.
Air-Conditioning
The most effective way to stay cool, especially during dangerously extreme heat, is with air-conditioning, whether it is central, a window unit, or a portable device that sits on the floor.
But just running the AC isn’t enough—it should also be regularly checked to make sure it’s working properly and most efficiently. And its filter should be changed regularly: When such a filter gets clogged, the AC unit or system has to work harder to pull air through, meaning it uses up more energy and may not work as well. The rule of thumb is to change an AC’s filter every three months. Checking and changing it is particularly important if you live in a very dusty or smog-prone area.
Though performing regular maintenance on a cooling device costs money, it’s much more expensive to deal with a broken one, Kear says. And air-conditioning is most likely to break when it is under the most strain, which generally occurs when temperatures are at their hottest—and you need it most. If your AC breaks during a heat wave, that is also the hardest time to find a technician to repair it because of high demand, Kear adds.
One big question people often have is whether to keep their air conditioner running when they’re not at home, particularly for extended periods of time, such as when they’re at work. The answer depends a little on what your goal is, says Brent Stephens, who runs the Built Environment Research Group at the Illinois Institute of Technology. If you want to maximize your comfort, leaving the AC on but turning it up a few degrees when you go out is likely the best route, he says. You can then put the temperature down when you get home. Or, if you have a programmable or remotely controllable thermostat, you can set it to become cooler 30 minutes to an hour before you come home. (Research shows many people don’t use these settings on their programmable thermostats, however.) If cost savings are your goal, there’s some research that suggests that turning the AC off during the day and then back on when you arrive home in the evening uses a little less energy, though not substantially less.
Windows
Sun-drenched rooms are cheery, but light equals heat. On a mild summer day, it might be okay to let light stream in through the windows. But during extreme heat, using reflective coatings, blackout curtains or other means of blocking incoming light can make a big difference, Seymore says.
If you have air-conditioning on and light streaming through the windows, the AC has to constantly work to keep the air cool. Because “cooling your home is going to be one of the biggest energy expenses you have,” Seymore adds, blocking light may mean your AC doesn’t have to work as hard.
In a pinch, you can use aluminum foil to block light. It’s best to put it on the outside of the window to stop the light from getting through at all. And using a layer of cardboard as insulation between the window and the foil can keep heat from stressing and potentially cracking a window.
Using weather stripping around windows can also help keep that hard-earned cooler air inside the home. Likewise, sealing any cracks and using draft blockers can prevent air leakage. For those who own their home, making sure the attic, walls and floor are well insulated will keep cooler air trapped inside better in summer (and do the same for warmer air in winter).
Fans
Fans are useful in a number of ways. Even if you have air-conditioning, they can help you more evenly circulate the cool air. The moving air from fans also makes us feel cooler because it puts more air in contact with our skin to carry away body heat. It additionally allows more of the sweat we generate to evaporate, which naturally cools the body down.
Ceiling fans are effective at cooling, with or without air-conditioning—but make sure they are circulating in the correct direction. In the summer, you want the blades to rotate counterclockwise to create a “downdraft.” (In winter, some fans can be reversed to create an “updraft” that mixes cooler air from below with warmer air from above and pushes the warm air back down along the walls to warm the space.)
Even without air-conditioning, fans can be used to help cool down a home: You can put box fans into windows early in the morning, when temperatures are at their coolest, to help funnel that air through a dwelling. Generally, you want a fan to face inward in a north-facing window and to face outward in a south-facing one to create a kind of tunnel that pulls air through, Seymore says. When temperatures rise to whatever level marks your personal edge of comfort, you can close the windows to help trap the relatively cool air inside and use window coverings to help keep as much heat from entering the house as possible, she adds. You don’t want to use fans in windows when it gets too hot—then you’re just blasting 95- or 100-degree-Fahrenheit (35- or 38-degree-Celsius) air into the house.
Appliances
To both minimize the amount of heat an air conditioner has to expel and keep room temperatures as comfortable as possible, avoid using heat-producing appliances as much as possible. This is particularly true during the peak heat of the day, when such energy use can also put more stress on the power grid and run up your electricity bill (many utility companies increase rates during peak hours). This can mean only running the dishwasher or washing machine and dryer at night. You can also avoid using the oven and stove and instead opt for the microwave or toaster oven if you need to heat up food.
Even the kind of lighting you use can make a difference, Seymore notes. LED lights emit very little heat compared with incandescent bulbs. “It’s all the little extra things that build up,” he says.