How Swamp Coolers Work (Evaporative Coolers)

If you’re the one who has to pay for electricity in your house, you are well aware of the fact that air conditioners cost a small fortune to run.

Some days you can live without it but some days it just gets so hot that you absolutely NEED to run it. Bummer for your wallet.

Do not despair, however! We do have good news.

Have you ever heard of swamp coolers? Don’t let the name deceive you, they have nothing to do with actual swamps or Shrek. And no, you don’t need to go to a swamp to get one.

No one really knows where the name originated from.

They’re also known as evaporative coolers. They’re a fabulous alternative to air conditioners.

Or maybe you have heard of evaporative coolers and are just curious to find out how they work. Whatever the reason, by the end of this article, you’re going to know everything about them.

If you’ve been looking for an affordable, environmentally-friendly way to cool your home then we may just have the answer to your prayers.

A Bit of History

What are we even talking about when we say swamp coolers? How do they work? What’s going on?

Well, you can actually feel how a swamp cooler works when you step out of a pool and instantly feel a chill when the wind blows. Or when you get out of the shower and feel a chill when the breeze comes through, even though it’s a warm day.

This small but potent discovery goes all the way back to ancient Egyptian days. In order to stay cool, they would actually hang wet blankets in the doors of their homes so that when there was a breeze, a small amount of cool air would come through.

Or if they were super bougie Egyptians, they would actually have servants fan them over jugs of water.

Fast forward a little bit to the time of our founding fathers and Benjamin Franklin had the same realization. He was one of the first people to actually offer one of the more modern descriptions and uses of evaporative cooling.

Okay, now that we know evaporative cooling has been around since forever, we should answer the question of what is actually going on here.

The Basics

Evaporative cooling works on one simple principle of nature that has always and will forever exist: when hot air passes over (or better yet, through) water, that air will cool off.

Pretty significantly, we might add.

That chill right out of the pool now makes perfect sense, doesn’t it?

Let’s get all scientific for just a second here.

So the dry air passes over water, the dry air will then absorb some of the cooler water, and then the temperature and vapor pressure of the water attempt to equalize with the air.

As a result, the water molecules actually turn into gas molecules, and the heat switches from the higher air temperature to the lower water temperature.

And since the air circulates naturally, the area around where this happens is also cooled! Brilliant, eh?

Anyway, unless you love chemistry, it doesn’t really matter what’s happening at a molecular level. All that matters is that with two basic ingredients, wind and water, you will get cooler air!

We know what you’re thinking – this is great and all, but I’m not going to hang wet blankets in all the doorways of my house just to make my rooms a few degrees cooler.

Fair enough.

We’ve come a long way since the Egyptians so there should be an easier and more efficient way to harness this effect. Lucky for you, there is!

This is where evaporative coolers come in.

So How Do You Get This to Happen All The Time?

We’re glad you asked! Don’t let us tell you what to do – if you want to be like the Egyptians and hang wet blankets in your doorway and write in hieroglyphics then be our guest!

Read no further!

For those of you who would like a slightly more efficient way to harness the natural power of evaporative cooling, read on.

Residential evaporative coolers have built upon this natural phenomenon. They actually use a fan to draw in the extremely warm and stale air, pull it inside the unit, and then allows the air to pass over water-moistened pads to be cooled!

Pretty smart, huh?

Through this process, the air can be cooled up to 20 degrees. It seriously is that efficient. Is it a 90-degree day? Perfect! You now have 70-degree air coming out of your evaporative cooler.

You now have cool air continually circulating and creating a breeze throughout the room.

By the time the air circulates throughout the room, this can lower the temperature of the room by anywhere from four to six degrees.

Not bad for a glorified fan.

One thing to note is that evaporative coolers are really only effective with hot, dry air. They’ll be the most effective during the hottest part of the day and you really only want the humidity to be 60% or less.

In fact, the lower the humidity, the better your swamp cooler is going to work. If the humidity is too high, they won’t work at all.

Which brings us to our next question.

Why Are They Not Effective in Humid Weather?

Very good question! We’re glad you asked. Before you ignore our warnings and run out and buy an evaporative cooler, even though you live in a very humid climate, you should consider this very scientific explanation for why they won’t work.

We know, it’s very unfair that everyone in Arizona gets to use a swamp cooler while everyone in the depths of Florida is shackled to an air conditioner.

But sometimes life just isn’t fair.

To explain why they’re not effective in humid weather, just think about exactly how they work.

If the air already has too much moisture in it, the cooler water that is trying to get into the air will have no room!

If you live in a place with 90% humidity, that’s only 10% room for the cooler water to sneak into! That’s not nearly enough to make any difference in the air.

Evaporative coolers also work their best when fresh air is constantly available. Having a window or a door open will greatly help with the air circulation.

Also, the evaporative process is going to naturally humidify the air. This is excellent if you live in a dry climate. It will relieve any dry air symptoms you might be encountering.

Plus, this can double as your humidifier!

If you have been looking for a humidifier for your room, consider purchasing an evaporative cooler. It’ll naturally humidify your room while also cooling it down.

This is a win-win in our book.

Swamp Coolers v. Traditional Air Conditioners

We talked a little bit about the differences between swamp coolers and regular air conditioners. Of course, there are pros and cons to both.

With that being said, however, we really love swamp coolers. Unless you absolutely need an air conditioner (and in some places, you really do!), then let us convince you why swamp coolers are better than air conditioners in a lot of different ways.

  • The first major selling point is the price! You can purchase a swamp cooler at a much much lower overall price than an air conditioner. There’s just fewer mechanics behind it so naturally, it doesn’t cost as much to produce.
    Still not convinced by just the price?
  • They also still come in all the major name brands such as Honeywell.
    You can find them pretty much anywhere you would pick up an air conditioner.
  • Swamp coolers are also significantly more energy-efficient than regular air conditioners.
    Don’t really care about the environment? Well, you should, but that’s beside the point. Being energy efficient can still benefit you which leads us to our next point.
  • Evaporative coolers cost a lot less to run vs. your typical air conditioner. How much cheaper?
    They can literally be up to three times cheaper to run! You can save a lot of money or run your evaporative cooler three times as often for the perfect summer.
  • We already touched on this but swamp coolers are much more environmentally-friendly. Not only are they more energy-efficient, but they use no chemicals whatsoever.
    Swamp coolers use an all-natural process and no additional refrigerants are added to cool the air.No pollutants or chemicals are being added to the air as a result. This is an enormous benefit! Air conditioners use a cocktail of chemicals to cool down the air and you don’t get any of those with an evaporative cooler.
  • One thing we can’t deny that air conditioners have over evaporative coolers is the fact that ACs will cool your house down to a much greater degree.
    Since they do use a lot of energy and chemicals, they are generally much more powerful. They work faster and have the ability to drop the temperature of the room 10 degrees plus. This is opposed to the six or seven degrees a swamp cooler can do.
  • Swamp coolers still come in a variety of large, big-name brands.
  • If you live in an area where the weather changes constantly and you’re having to take the AC in/out, then just know that evaporative coolers are much easier to set up than traditional air conditioners.
  • Air conditioners will significantly dry out the air in your room while swamp coolers are actually putting moisture back into the air. Again, perfect if you live in an arid climate.

How Big of a Swamp Cooler Will I Need?

Good question! You want to make sure you get the right size. Otherwise, if you get one that’s too small, it will be working extra hard to cool your room, therefore, wasting energy.

Then you’d lose one of the main benefits – energy/money savings!

So how do you know?

There’s actually a simple formula you can use to figure it out.

Take the square footage of your room, multiply it by your ceiling height, then divide by two. Voila!

That number will give you the CFM (Cubic Feet per Minute). Swamp coolers are measured in this and now you can figure out exactly how big of a swamp cooler you’ll need.


There you have it! Pretty much every single thing you need to know about swamp coolers. They’re cool, right?

If you live in a dry climate, they can be the perfect alternative to getting your house down to a livable temperature without having to spend your whole life’s savings on electricity for an air conditioner.

Justin Howe

Electrician and DIY specialist Justin deleted his own successful tech blog to write expert product reviews and buying guides together with his friend Robert.

Justin Howe

Electrician and DIY specialist Justin deleted his own successful tech blog to write expert product reviews and buying guides together with his friend Robert.