Try a desert trick. When the air outside is dry and cooler than the air inside, hang a damp sheet in an open window. “That’s what we do here in Death Valley,” says Dale Housley, a ranger at Death Valley National Park. Incoming breezes are cooled by the evaporating water.

Block the sun. Closing curtains and blinds (ideally with sun-deflecting white on the window side) can reduce the amount of heat that passes into your home by as much as 45 percent, according to the U.S. Department of Energy.