Swamp coolers and desert coolers are a type of evaporative cooler that combine wind and water in an integrated unit. They use a fan to either pull or push warm air through a water-soaked pad.
For hot, dry weather a swamp cooler / desert cooler or other kind of evaporative cooling could be the best outdoor cooling solution for you.
"Swamp cooler" and "Desert cooler" are both expressions for evaporative coolers that use water-soaked pads.
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.
We get the term swamp cooler because these are often used indoors where the unit is being used may not get enough air flow. So the air can become very humid and "swampy."
If you want to learn about other evaporative coolers see our pages on misting systems and misting fans.
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 work best in the hottest, driest part 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 the 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.
To learn more about how weather affects the cooling capacity of evaporative coolers, go to our weather page. There you'll also find a link to a site that can give you the average temperature and relative humidity levels for your area.
"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.
This charts doesn't show the additional 4 - 8° F / 2 - 4.5° C of cooling from the breeze a swamp cooler creates. They can move a lot of air, like regular outdoor fans. So in addition to cooling from evaporation, you'll feel some extra cooling from the fan.
In fact, many swamp coolers have a feature that lets you turn off the evaporation function and use the fan only -- for ventilation or mild cooling in the most humid environments. In more humid weather you will feel less cooling from the evaporation, but you'll still feel the cooling breeze from the fan.