Evaporative cooler or AC: which is better in Phoenix?

The swamp cooler vs AC question in Phoenix doesn’t have one answer for every house. A swamp cooler, or evaporative cooler, is cheaper to run and works well in dry heat. A refrigerated air conditioner costs more to run but doesn’t depend on the weather being dry. Which one fits depends on how you live through the humid part of the summer, how you feel about water use, and how much upkeep you’re willing to take on.

How a swamp cooler and an air conditioner cool differently

An evaporative cooler pulls outdoor air through water-soaked pads. The water evaporates and cools the air by 15°F to 40°F before it’s blown into the house, according to the U.S. Department of Energy. It keeps bringing in fresh outdoor air, so it needs somewhere for indoor air to go: the DOE says to open windows or vents on the side of the house away from the wind, about 1 to 2 square feet of opening for every 1,000 cfm of cooling capacity.

A swamp cooler also adds moisture to the air. University of Arizona Cooperative Extension describes evaporative cooling as lowering air temperature and raising humidity at the same time. That’s why the DOE says coolers are only suitable for areas with low humidity.

A central air conditioner works differently. It doesn’t use water directly, and it doesn’t need open windows to move air through the house.

Swamp cooler vs AC on electricity and water

On energy, the evaporative cooler comes out ahead. The Department of Energy says evaporative coolers cost about half as much to install as central air conditioners and use about one-quarter as much energy. University of Arizona climate researchers put it as air conditioners generally using two to four times more electricity than swamp coolers. In their example of a typical 2,000-square-foot Tucson home, a swamp cooler can use as little as 250 kilowatt-hours in an average month, compared with about 850 for an air conditioner.

Water runs the other way. The same researchers found that in Tucson summer conditions (May through September), a swamp cooler working at 75 percent efficiency uses an average of 150 gallons of water a day, while an air conditioner uses no water directly, though the same researchers note that generating the electricity it uses does consume water. The DOE also notes that coolers need more frequent maintenance than refrigerated air conditioners, including regular pad changes and cleaning. See how to maintain a swamp cooler in Phoenix for what that involves.

How monsoon humidity changes the answer

Arizona’s monsoon season runs from June 15 to September 30, as defined by the National Weather Service. Arizona State University notes that a 55°F dew point in Phoenix is linked to enough moisture in the air to generate thunderstorms. For a swamp cooler, that moisture is the problem: University of Arizona climate researchers write that evaporative cooling works best in the dry months of summer, and that during the monsoon, when outside air is already moist, a swamp cooler’s effectiveness is limited.

An air conditioner doesn’t rely on evaporation, which is why a home with both systems can turn to it when the humidity comes in. If yours seems to run nonstop, see why your AC runs all day in a Phoenix summer.

Which one fits your home

Some Phoenix homes have both and use each when it works best. One Phoenix homeowner described that approach to KJZZ: he runs the evaporative cooler while the air is dry, then watches the dew point and switches to air conditioning when the monsoon humidity arrives.

A few questions can help you decide:

• How much of the summer can you ride out with a cooler? In the dry months it cools on less electricity, though the DOE notes it won’t cool the house as low as an AC; during the monsoon it falls behind.
• Are you comfortable with the water use? A cooler trades lower electricity use for daily water use.
• Will you keep up with maintenance? The DOE says coolers in hot climates need monthly checks. If yours sits on the roof, working up there in summer heat is dangerous, so plan to hire help if you can’t do it safely.
• Do you keep windows closed? A cooler needs open windows or vents to work; an AC doesn’t.

For homes that have both, the choice isn’t one or the other. It’s which one carries the load in which part of the year.