The cool-air fan is used in hot dry climates to cool and humidify the air. The air coming out of the 5051 is normally 3-5 degrees cooler then the ambient room temperature. The unit works by pumping water from the main tank to the filter which looks similar to a cardboard honeycomb. The filter is wet and as the air passes over the filter the water evaporates which lowers the temperature of the air, thus cooling the room.