What Is A Swamp Cooler?

Swamp coolers / desert coolers are a type of evaporative cooler that combines wind and water in an integrated unit. They use a fan to either pull or push warm air through a water-soaked pad.

They need electricity and water, so you can read here about their water and energy use. They use less electricity than a portable air conditioner and reduce temperatures more than a basic outdoor fan.

Swamp Coolers vs. Desert Coolers vs. Air Coolers

“Swamp cooler,” “air cooler,” and “desert cooler” are all terms for evaporative coolers that use water-soaked pads which hold water while air flows through them. This cools the air down as it flows through and blows out the cool air.

We get the term swamp cooler because these are often used indoors where the unit being used may not get enough airflow. So the air can become very humid and “swampy.” “Swamp cooler” is generally the more popular term.

We get the term desert cooler from the fact that these coolers work so well in hot, dry climates. They were used hundreds of years before electricity. People would put up water-soaked sheets that the hot, desert breezes would flow through, providing simple, efficient cooling.

There is a lot of advertising that calls air coolers “air conditioners” in the hopes of getting your attention. But air coolers are not the same as air conditioners.

Air Coolers or Swamp Coolers vs. Air Conditioners

Air coolers / swamp coolers use water-soaked pads to cool an area with evaporative cooling and a fan. They need fresh air where they are being used to keep humidity from getting too high. This makes them a good solution for partially enclosed outdoor areas such as a patio or deck next to a wall or building. Without fresh air, the cooling effect is reduced and the air can start to feel “swampy.” They are much easier to set up than air conditioners but need to be refilled with water – usually in an onboard tank or with access to running water like a garden hose.

On the other hand, air conditioners use refrigerant and a fan to replace hot air with chilled air. They are most effective in fully enclosed areas such as a tent with sidewalls. Outdoor setup usually includes one hose to push cool air into an area and another hose to pull hot air out. Unlike air coolers, they reduce humidity, which adds to their cooling effect.

How, When, and Where Swamp Coolers Work Best

When water evaporates, it cools the air immediately around it. (If you’ve ever felt cold when you step out of a pool or shower, it’s because of the evaporative cooling effect.) This makes it a great cooling method on hot days. Pads that hold water are positioned near a fan that blows out this water-cooled air, cooling an area by anywhere from 3°F / 1.5°C to as much as 30°F / 16.5°C, depending on the humidity and the air temperature.

Swamp coolers provide the most cooling in the hottest, driest times of the day.

Evaporation adds more moisture to the air. Air that already has a lot of moisture in it can’t hold much more of the cool moist air that comes from a swamp cooler; air that is naturally dry can absorb more. Also, air that is naturally humid in the morning will be able to absorb more of this additional cool moisture as the sun rises in the sky and the air gets hotter.

Heat causes evaporation that cools us. Swamp coolers use the heat from the outside air to trigger that evaporation. So high temperatures with low humidity are the best conditions for a swamp cooler.

“RH” or “relative humidity,” refers to how much water the air can hold relative to how hot it is. Hot air holds more moisture than cool air. A level of moisture in cool air may measure 40% RH, but as the sun rises and the air temperature increases, that same amount of moisture might be measured as 30% RH. So your swamp cooler will be more effective in the middle of the day when it’s hotter. And that’s exactly when it’s needed most.

Compare the humidity level for your area with the numbers on the following chart. This chart shows how much cooling you can expect from evaporative coolers based on air temperature and relative humidity.