Evaporative Cooling — When It Works Best,
Which Kind is Best for You?

lounging by a misting fan

Evaporative cooling could be your best solution for outdoor cooling if your weather is hot & dry and you have access to water.

Swamp coolers, misting systems and misting fans ALL use evaporative cooling.

Which is best? You can sort it out by simply knowing some basic differences.

All of these cooling method belong to a general category of products that use water and evaporation to provide cooling. Misting systems and misting fans use a water mist while swamp & desert coolers use water-soaked pads.

"Swamp cooler" and "Desert cooler" are different terms for the same thing – evaporative cooling that uses water-soaked pads.

swamp cooler refreshes an outdoor marketThe term desert cooler comes from the fact that these coolers work so well in hot, dry climates. Their use goes back long before electricity was harnessed.

We use the term swamp cooler because these are often used indoors where the cooling unit might not get enough air flow. Since evaporative cooling adds moisture to the air, in an enclosed area the air can become very humid and "swampy."

When you search for these coolers you'll find product descriptions might use "swamp cooler" and "desert cooler" interchangeably with "evaporative cooler," or they'll just use the term "evaporative cooler."

How is evaporative cooling different
from other cooling solutions?

An evaporative cooler is often called a cooler or air cooler to differential it from an air conditioner, which works in a different way and has different benefits and drawbacks.

Other cooling solutions do not use water. An air conditioner actually decreases the water in the air (humidity). It forces special chemicals (refrigerants) to evaporate and condense in a closed system of coils and a fan blows air over the cold coils. A fan uses "wind chill" (convective cooling). And shade uses a physical barrier to block the source of heat.

Evaporative cooling use the natural process of evaporation to cool the air. All that's needed for this is some hot air and some cool water. They need fairly dry conditions to provide the most cooling. The more humid the air the less cooling.

On a hot day, when warm air comes in contact with water, it makes the water evaporate. When the water evaporates, it cools the air immediately around it. (If you've ever felt cold when you step out of a shower or pool, it's because of the evaporative cooling effect.)

Evaporative cooling works 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 an evaporative 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.

misting system cools a patioHeat causes the evaporation that cools us. Evaporative 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.

"relative humidity," or "RH" refers to how much water the air can hold relative to how hot it is. Hotter air can hold more moisture than cooler 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, misting system or misting fan will be more effective in the middle of the day when it's hotter and drier. Perfect.

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

You can get the average temperature and relative humidity levels for your area at Weatherbase.com

chart showing how many degrees fahrenheit of cooling you can expect from a swamp cooler based on relative humidity and air temperature

Not noted in this chart is the additional 4 - 8° F / 2 - 4.5° C of cooling from the breeze a swamp cooler or misting fan creates. In addition to cooling from evaporation, you'll feel some extra cooling from these methods.

Interested in learning even more?

You can learn more about each of these evaporative cooling solutions by visiting our pages for swamp coolers & desert coolers, misting systems, and misting fans.

To see a simple comparison of all the different outdoor cooling solutions we cover, visit our comparison page. Visit the evaporative coolers section while you're there.

To learn more about how weather affects each cooling method, go to our

weather page.