An evaporative air cooler is a type of air conditioner that works by harnessing the power of evaporation to cool air temperatures. When water evaporates, it turns from liquid to gas. As it does so, the highest-energy particles leave the water first, and this leads to a drop in temperature. This is why a moist cloth on your forehead feels good on a hot day — it’s actually helping to lower your head’s temperature as the water evaporates.

The same scientific principles apply to the evaporative cooling process when it comes to your home’s air. In a dry environment, the simple process of evaporation can help lower the temperature of the air. You may have felt this for yourself if you’ve ever misted the air around you to feel cooler on a hot summer day. An evaporative air conditioner uses the same idea, but it adds technology to make the process more efficient — and less messy — than just spraying a room with water and hoping for the best.