Keystone evaporative air coolers, also called swamp coolers, are intended for use in hot dry climates where the humidity is low (less than 60%). Evaporative air coolers can lower indoor temperatures by as much as 15 to 20°F by combining the natural cooling properties of water with a steady breeze from an efficient air moving system. Swamp coolers use nearly 75% less electricity than air-conditioners and use no ozone damaging refrigerants. Also, the water saturated pads act like a filter, removing dust from the air. Buyers Note: For those living in more humid climates, consider using Keystone portable air conditioning units or window air conditioners.