Those living in dry, hot climates have long heralded swamp coolers as effective at cooling and humidifying homes. An alternative to an air conditioner, a swamp cooler uses evaporation, rather than chemical coolants, to lower the temperature of air. In ideal conditions, a swamp cooler can make a difference of a staggering 30° F (17° C).

A swamp cooler uses the basic principle of evaporation along with simple technology and electrical power to create cold airflow. First one motor pumps water into pads of a fibrous, absorbent substance similar to hay, called cellulose. Then another motor powers a fan that pushes air through the pad, always pregnant with fresh water. When the entering air is very hot and very dry, some of the water evaporates into it. Evaporation needs molecular energy, otherwise known as heat, which ends up reducing the temperature of the air and adding humidity. Finally, the cooler air is pushed through a duct into a central location in your house, like a hallway or living room.

Not only does a swamp cooler cool air, but the atmosphere is more pleasant. The chilled air is slightly damper and always freshly recirculated. This gives the swamp cooler many advantages over an air conditioner. Air conditioners recirculate old air, and actually reduce the humidity, which can prove uncomfortable and unhealthy in a desert climate. A moderate degree of humidity keeps our mucous membranes moist, therefore improving immunity. Also, swamp coolers use significantly less energy, so they conserve electricity (though not water) over air conditioners.

A swamp cooler works best with temperatures above 80° F (27 °C) and humidity below 30%. This makes them ill suited for hot and wet climates, such as found around the Gulf of Mexico. The air is already so heavy with humidity, very little additional water will evaporate, and the exterior air will be almost the same temperature as air that already passed through the swamp cooler. Instead, swamp coolers can be found on roofs and in windows of many satisfied customers in the Western United States, particularly California, New Mexico, and Arizona.