Buying a , often called a "swamp cooler," is a cost-effective, eco-friendly way to stay cool in hot, dry climates. Unlike air conditioners that use chemical refrigerants and compressors, these units use a simple fan to pull warm air through water-saturated pads, naturally dropping the temperature by as much as 15°F to 40°F . Essential Factors to Consider Evaporative Coolers - Department of Energy