An evaporative cooler uses the water to cool off air brought in from outside the house. Water is pumped onto the pads the air passes over, and the air loses its heat to the water—this is evaporative cooling. Electrical power goes to the pumps wetting the pads and to the blower fan.

How effective are evaporative coolers?

According to the US Department of Energy (DOE), an evaporative cooler can successfully reduce the ambient temperature by 5 to 15 degrees—but even the DOE is quick to clarify that this process works only in areas with low humidity.

Do you need to have a window open with evaporative cooling?

You can attain balanced air flow by installing ducts in each room or opening windows when the cooler is in use. A window should be open just enough to allow air pressure inside a room to slowly and quietly close the door to that room. ... However, the window is open too far if the door doesn't move at all.