The dog days of summer: They’re hot, and maybe humid in your neck of the woods, too. One surefire way to get some relief during those 100-degree days — and some shut-eye on those nights when the thermometer doesn’t dip below 85 — is to turn on the air conditioning. Of course, every turn of the dial strains not only your wallet, but also our aging power grid.

In recent years an alternative to A/C has become increasingly popular: the swamp cooler. These devices, also called evaporative coolers, use fans to draw  in air from outside and blow it over water-saturated pads, causing the water to evaporate into the air, thus cooling it as it enters your home. (If you’re having a hard time drawing a mental picture, lick your hand and then blow on it — your skin feels cooler because of evaporation.) Manufacturers claim that swamp coolers are more eco-friendly than A/C units, but should you believe the hype?

The Claim: Swamp coolers are greener than air conditioners.

The Facts: According to the Department of Energy, evaporating water into the air in arid regions is a natural, energy-efficient way to cool air by as much as 30 degrees. Swamp coolers cost about half as much to install as window A/C units, and use up to 75 percent less electricity. One window should be open when running a swamp cooler, which pushes warm air outside as cool air blows in. The influx of fresh air is a definite perk of swamp coolers, as opposed to window A/C units, which recirculate air. According to scientists at Lawrence Berkeley National Laboratory, evaporative coolers can meet all or most of a house’s cooling needs, but only for houses located in a low-humidity area. In general, that means they’re ideal in the Rocky Mountain region, the Northwest, and the Southwest. In wetter climates, though, swamp coolers would just add humidity to the air. They also evaporate anywhere from 3 to 15 gallons of water a day — something that people living in drier climates should take into consideration.

The Conclusion: The energy efficiency of swamp coolers makes them a greener option than air conditioners, despite their need to consume about a shower’s worth of water every two days — but they’re only effective if you live in a dry climate. And if water conservation is an issue in your town, check with your water utility before purchasing one.

Story by Alisa Opar. This article originally appeared in Plenty in June 2007. This story was added to in June 2009.

Copyright Environ Press 2007.