Thinking about buying an evaporative cooler? The internet is full of all kinds of information about these small household appliances, but not all blog posts are created equal. When it comes it researching products, where you get your information is important. In particular, opinions about evaporative coolers vary widely, and this is usually due to one crucial factor: location.

Where you live makes a big difference in how effective evaporative cooling will be in your house. In general, evaporative coolers work best in arid climates with low relative humidity. To understand why that's the case, it helps to know exactly how evaporation works to lower the air temperature.

How Evaporation Cools Things Off — Including Your Living Room

Most people intuitively know that evaporation cools things off, because they have it happen to their bodies every summer when they sweat. When water evaporates from your skin — whether you've just come out of a swimming pool or your body made its own cooling fluid and pushed it out of your pores in the form of perspiration — it lowers the temperature of your skin. Since your skin is the largest organ in your body, this can very quickly bring down your body temperature and keep you from becoming feverish when the season heats up.

But why does this work? The answer is a little complicated because it has to do with physics. If you think back to your high school science classes, you may recall that all matter has three states: solid, liquid and gas. This is very easy to see with water, which freezes solid into ice at 32 degrees Fahrenheit and evaporates into a gas, or water vapor, at 220 degrees Fahrenheit — also known as its boiling point.

But it's the molecules left behind that are important to the cooling process. As molecules break away, they take some heat with them with their high-energy motion. The molecules of water left behind are left with less heat in the process, which cools the water down. When that cooler water is touching your skin — or the air in your living room — it lowers the temperature and makes things a whole lot more comfortable thanks to this natural cooling effect.When water evaporates and changes into a gas, it's because the kinetic energy of its molecules increases when the water's temperature rises. Imagine little molecules dancing around slowly at room temperature, but faster and faster once someone lights a fire under their metaphorical feet. When it's hot enough, the fast molecules break away and fly into the air — that's evaporation.

Why Evaporative Air Coolers Work Best in Dry Climates 

Evaporation happens faster when the air is dry — that is, when the relative humidity is low. Relative humidity is a measure of the moisture that's already in the air, and there is a limit to how many water molecules the air can hold in total. If it's very humid, water will evaporate slowly, or not at all. That's because there's simply nowhere for those water molecules to go when they try to jump away, no matter how hot you make the liquid. Instead, you'll get condensation that drips off your walls and windows.In general, natural evaporation is kind of a slow way to cool things off. You aren't using boiling water to speed things up, so you have to rely on the very gradual evaporation that takes place at non-scalding room temperature. If you're talking about a puddle on the sidewalk, you know that it can take hours or even days to disappear. This is all dependent on the weather.

If water can't evaporate efficiently, it can't cool anything either. That's why evaporative coolers work best in arid climates. In the United States, this means Southern California, the Southwestern states of Nevada, Arizona, Utah, New Mexico and Colorado, and the western portion of Texas. Here humidity levels are almost always super low, which means quick evaporation is a given — and that means your swamp cooler will help lower the indoor air temperature by 15 or even 20 degrees.

Unfortunately, evaporative cooling systems don't work nearly as well in humid climates. When the water can't dissipate, it can't cool air to a comfortable level. In fact, an evaporative swamp cooler used in humid conditions can actually make you feel worse, since it will be adding moisture to the air, which will in turn make it impossible for perspiration to evaporate and cause that sticky feeling that can be so miserable on humid days.

The bottom line? Evaporative coolers work very well in dry climates, but not in humid areas like the states east of the Mississippi River. If you're not sure about your hometown, check our handy map here.

How Evaporative Coolers Harness the Power of Evaporation

Now that you know that you need to start with dry air for a swamp cooler to work, it's time to dig a little deeper into how an evaporative cooler makes evaporation work quickly enough to cool the hot air in your home. In general, all portable air coolers have a water basin, a cooling pad and a fan to get the job done. The reservoir holds the water supply, which is slowly soaked up into specially designed cooler pads. These are very absorbent and often have a honeycomb or fin-like shape to create lots of surface area. The more surface area there is, the more water can evaporate at one time, which makes cooling more efficient.

The evaporative cooling process is further assisted by the fan, which blows dry, fresh air across the wet pad to keep airflow constant. As the dry air hits the pads, those jumpy water molecules can fly away and drop the temperature. The fan also blows that cooler air right into your room, where you want it, instead of having it hover around the cooling pads.

Bonus Feature: In most evaporative coolers, the cooling pads do double-duty as an air filter. As fresh air blows across the pads, tiny particles like dust and pollen stick to the pads and are held in place instead of being blown around your house, where they can cause allergies or bother people with respiratory troubles.

How to Get the Most Out of Your Evaporative Cooler

Wrong Climate:
An evaporative cooler isn't designed for humid weather. If you're in a borderline area, it's probably best to have a back-up air conditioning system for humid days. A portable air conditioner is a great choice if you don't have central air and need a system that will help you cool off when humidity spikes. When people experience issues with a swamp cooler not working well to cool a room, it's usually due to one of the following problems:

  • Filter Build-Up: Because the cooling pads act like a filter, it's important to keep them clean of debris so that water can continue to evaporate efficiently. Either scrub your cooling pads to clean them or replace them when they get dirty.
  • Air Changes in Your Home: As you run your swamp cooler, it will add moisture to the air and raise the humidity levels gradually over time. As humidity rises, the cooling becomes less efficient. To combat this basic truth and keep the cold air coming, it helps to open windows around the house so there's always a supply of dry air coming across the cooling pads. This will also keep it from getting clammy in your house.
  • Improper Sizing: Like air conditioning systems, swamp coolers are designed to cool a certain area. If you buy a cooler designed for 1,000 cubic feet but your open-concept living room is really more like 5,000 cubic feet, it will never be able to keep up with the demands you're putting on it. Always measure your space and check the specs on any unit you're considering to make sure you get the right size cooler for the job.

When you read reviews of swamps coolers, whether for specific products or for the concept in general, be sure to check where the reviewer lives (many reviews come complete with the city and state). If someone says their cooler didn't work for them, make sure they live in a climate that's appropriate for these systems in the first place. If you're trying to figure out if one will work for you, focus on reviews from users who live near you to get a sense of their success rate.

So Do Swamp Coolers Work?

Yes! When you live in the right climate for an evaporative cooler and you make sure you have the right airflow happening in your home, a swamp cooler is an energy-efficient way to get comfortable during cooling season. Because they don't use as much electricity as traditional air conditioners, you'll notice far lower energy bills if you make the switch. Think of it as better living through science: If you live in the desert, you can definitely take advantage!

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