Evaporative Coolers: What They Are and How They Work

When you’re considering going to buy an evaporative cooler as an economical and effective way to beat the heat, especially when you live in a less humid climate such as Arizona, for example, you’ll find plenty of options.

There are many makes and models of evaporative (or swamp) cooler out there, with some making rather impressive claims with regard to performance and usability.

There are also some surprisingly attractively-priced models available. It’s good to know how well the claims tend to stack up against reality.

So I’m taking a closer look at the reality of owning and running one of these coolers to see what you’d get for your hard-earned money.

How an Evaporative Cooler Works

evaporative coolerAn evaporative cooler (or swamp cooler, the two names mean the same thing) works by pulling in dry air from the space to be cooled, adding moisture to it, then blowing out chilled and humid air into the space, effectively reducing the ambient temperature but raising the relative humidity in the process.

A powerful fan blade is responsible for the airflow, just like a regular fan does. The fan pulls air in through the vents on the back and sides of the unit, passes that air through a wet membrane, then accelerates the now chilled air out through the front of the unit.

The cooler has a reservoir at the bottom of the unit that holds water. In some models, a pump pulls the water to the top of the unit and distributes it over the porous pads that cover the air passage inside the unit.

As the fan pulls air through the wet pads, that air picks up additional moisture. Instead of coming out as a mist, as it would in a misting cooler, the now cold, damp air raises the humidity level.

That may sound like simply taking Arizona’s dry heat and adding, say Florida’s humidity. However, it’s actually a lot more comfortable than it sounds. The internal fan keeps air moving over you while the extra moisture absorbs heat from the space, causing the temperature drop.

It’s a lot more effective than the basic airflow of a fan alone.

NOTE: Evaporative coolers work best when the relative humidity is below 60%. Any higher than that and the effectiveness of the mositure absorption of the air is reduced and so is the cooling effect.

Swamp Cooler Terms to Know

There are a few important terms associated with portable swamp coolers that it’s handy to know:

CFM (cubic feet per minute): A measure of airflow or how much air is moved by the unit in a given time. The higher the value, the greater the volume of air that is moved through the unit and in the space. This is related to the cooling effect.

Airspeed:  This is what it sounds like, the speed of the air expelled from the unit. Models that are able to force air out faster and farther effectively cool larger spaces better.

Current Draw: This is the amount of electricity the unit uses, measured in watts. Evaporative coolers are surprisingly frugal when it comes to drawing energy. This is important to know if you’re running on solar power or using a generator. That means the more energy-efficient the unit, the better.

Tank Size: This is the volume of the water tank, generally measured in gallons. While excess water drains back to the tank, some of the water is evaporated into the air. The greater the tank’s capacity, the ore water it will hold and the less often you have to refill.

Noise Level: Again it’s what it sounds like. It’s common to be in relatively close proximity to a swamp cooler, so the less noise it makes, the more comfortable it is on the ear.


Owning a swamp cooler is a great way to keep cool without using very much electricity to do so. Typical models use no more than 100 watts of power, compared to 1,000 – 2,000 watts used by many similarly sized portable air conditioners.

If you live in an area with high humidity, then a portable air conditioner or where possible a window air conditioner may be your best choice to keep cool. However, as long as your climate is not humid, you’re good to go with one of these amazing, eco-friendly coolers!