Evaporative coolers really do a great job of cooling indoor air as long as the outside humidity is low. While cooling a house of average size using air conditioning might cost about $300 per month in an extremely hot and arid climate, cooling that same house under the same conditions using an evaporative cooler would probably cost no more than $70 per month. Also known by the term "swamp cooler," evaporative coolers work, as their name suggests, through the process of evaporation. Pads are soaked in water. Air is drawn through them and cooled as a result. The cool air is blown into the house or building and, as you might expect, the inside temperature is dropped considerably. Depending on the humidity, evaporative coolers may be just as effective at cooling the air inside a building as would be the case with air conditioners, but if the humidity gets too high this is no longer the case, which explains why evaporative coolers are seldom used in climates where high humidity is common.