Evaporative coolers, also known as swamp coolers, are cheaper and more cost-effective than air conditioners. They create a lot of cold air using much less energy, so it’s no wonder they’re an appealing choice for anyone who wants to save money while keeping cool (See What Are Evaporative Coolers? Here’s Everything You Need to Know)

What’s not cool is when your evaporative cooler doesn’t actually make you cooler, when it’s not working or not working well. So, to help avert any “heated crises,” we’ve put together a few secret hints and troubleshooting ideas to help you get more out of your evaporative cooler.

Humidity is the Bane of Evaporation

When water evaporates, it uses the heat in the air as fuel for its transformation from water to vapor. The heat gets absorbed and suspended in the water vapor, lowering the temperature of the surrounding area. The faster the water evaporates, the more heat gets used up and the faster the temperature drops. This is exactly what happens in an evaporative cooler. Water is pumped up and poured onto a specialized cooling pad that has warm air blown through it by a high-powered fan. The water absorbs the heat and evaporates and cool air gets blown out the other side.

The rate of evaporation is inversely proportional to the humidity of the surrounding area. When humidity is low, the air’s capacity to store water is very high and evaporation happens very quickly. When the humidity is high, though, the air is already saturated with moisture and its ability to absorb more water vapor is very low – evaporation happens slowly. That’s why humid weather is so much more uncomfortable than dry heat. The sweat your body produces sticks to your skin instead of evaporating and cooling you down.

Humid weather is bad for evaporative coolers as well. As humidity rises, the temperature difference between the from the cooler and the air around it falls, until eventually it becomes little more than a fancy looking fan.

Usually, we do not recommend swamp coolers for places that experience a lot of humidity in the summer because evaporative cooling isn’t effective in that sort of environment unless you know the secret to use your evaporative cooler as a supplement to your central air conditioning. What is it? Well, besides cooling the air, air conditioners also dehumidifies it. In fact, dehumidification takes place even if you run your AC at fairly high temperatures. So you can set your central AC at 80°F or higher – which will save you a bundle on whole-house cooling costs – and use a portable evaporative cooler to lower the temperature in the one or two rooms you’re actually using. The dry air will bring your evaporative cooler back to life. (See When Should You Buy an Evaporative Cooler? Know Your Humidity Levels)

The Secrets to Keeping Cool with Evaporative Coolers

Everyone Needs to Vent

With an air conditioner, a room or building needs to be closed up tight for it to be effective. The opposite is true with a swamp cooler, which relies on a consistent stream of fresh air in order to work.

If you find your portable evaporative cooler isn’t cooling things down, make sure the cooler is positioned near an open door or window. If it already is, open window on the opposite side of the room to create a cross breeze to draw the hot air out. Usually, 1 or 2 square feet per 1,000 CFM of cooling capacity is sufficient to allow hot air and humidity to be pushed outside. Experiment by adjusting your windows to see which create the best breeze and how wide they need to be open in order to control the amount of cooling.

The Secrets to Keeping Cool with Evaporative Coolers

Ice, Ice, Baby

A secret technique a lot of homeowners use on their evaporative coolers is adding ice to the water tank in order to increase its cooling capacity. It seems reasonable, ice makes air colder, so adding ice to your cooler should make it colder. In fact, many coolers feature special ice compartments and gel ice packs to help generate this cold air effect.

In actual practice, adding ice to your swamp cooler only has a limited effect. Yes, cold air radiating from the ice will be blown out by the fan, so you’ll feel an extra burst of cold air if you’re standing right in front of it, but it won’t improve the rate of evaporation, or remove heat from the air the way evaporation does. It’s the combination of temperature and humidity in the ambient air that determines how much of a boost ice provides, not the ice itself. In fact, adding ice to your evaporative cooler might actually hamper the cooling process.

Water has to heat up in order to evaporate. The colder it is, the longer it takes to warm up. If it’s really cold, it might actually drip out of the cooling pad before evaporation can even take place. If you’re having trouble getting cold air out of your cooler, try replacing the ice and cold water with room temperature water (never hot water!) and see if the effect is improved.

The Secrets to Keeping Cool with Evaporative Coolers

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