What is a swamp cooler? Also known as an evaporative cooler, this device—which is about the same size as a room air conditioner—lowers the temperature in a home simply by adding moisture to the air. Although it has limits on where and how well it works, it's a cheap, efficient alternative to a regular air conditioner—it's well worth considering if you want to save money.

According to the most recent figures from the United States Energy Information Administration, swamp coolers are used in only 2% of homes nationwide, yet in states along the Rocky Mountain range, swamp coolers can be found in as many as one-quarter of all homes. The reason for this is air climates in this region are ideal for swamp coolers to work their magic.

How a swamp cooler works

Swamp coolers date to ancient Egypt (yes, we're serious), where homeowners would cool their home by hanging wet towels or blankets over windows and doors; wealthier citizens would have servants fan them across containers of water. Today, swamp coolers work by the same principle: A motorized fan pushes air through damp pads, which moisten and cool the air before blowing it into its surroundings.

When air passes over water, microscopic molecules of water evaporate into the air, turning from a liquid into a gas. This process eats up heat, thus cooling the air around it.

According to John Ricart, owner of West Coast Plumbing and Air in Phoenix, swamp coolers can drop the temperature anywhere from 5 to 15 degrees Fahrenheit—all for a fraction of the cost of running AC.

However, having an arid climate is a must. If the air is already humid—in other words, if your typical humidity is over 50%—a swamp cooler won't work. So if you tend to have hot, sticky summers, a swamp cooler isn't for you. Sorry New York! See you later, South Carolina!

Swamp cooler cost and installation

Swamp coolers vary in size, and some can be installed in a window, similar to a window AC unit. There are also models with wheels on the bottom, allowing you to move the swamp cooler from room to room the way you might move a fan to cool different areas of the home. Swamp coolers are also less expensive than air conditioners, with smaller units going for anywhere from $150 to $350.

Although swamp coolers operate as plug-in appliances, there's also the option of a down-flow installation, typically done by a contractor who will install ductwork throughout your home and mount your swamp cooler on the roof, allowing the unit to blow cool air into many rooms at once. Costs for this sort of project vary by area and the size of your home, but homeowners can expect to pay anywhere from $1,500 to $5,000 for the whole job.

Swamp cooler vs. air conditioner

The Department of Energy estimates that an evaporative cooler uses about a quarter of the energy consumed by a central AC system, and the purchase cost is about half that of central AC.

Beyond the power usage, there are other green benefits to swamp coolers: They don't require the use of refrigerants, the chemicals used in AC units that have been linked to global warming.

What's more, a quality unit can last for as long as 15 years, according to replacement estimates from the International Association of Certified Home Inspectors. By comparison, your typical air conditioner is expected to last just five to seven years.

Limits of a swamp cooler

Although you can still find swamp coolers in plenty of homes and home supply stores, Ricart says they're less common than they were 10 or 20 years ago because they're harder to control than their AC counterpart—and, as we mentioned, not too effective in especially hot climates.

"A swamp cooler is never going to get you below 65 or 70, and that's on a good day," he says. On days when the mercury rises above 100, a swamp cooler might just drop the temperature in a home into the 90s.

Ricart also warns customers that the moisture fed into a home can wreak havoc on wood furniture and heighten the risk of mold growth, if it's not controlled. "It can make everything in the house soggy," he says.

Like many appliance purchases, this is one where you'll need to weigh the benefits against the drawbacks to choose what's right for your home.