Evaporative coolers, also known as swamp coolers, can help cool the air in a building by drawing warm air through a pad that is soaked in water. As the air passes through the wet pad, some of the water in the pad evaporates into the air, thus cooling it off.
Depending on the specific outdoor temperature and the size of the cooler and its fan unit, evaporative coolers can cool the air coming into a room by as much as 15 to 40 degrees Fahrenheit, This can have the effect of lowering the overall temperature of the room by somewhere between 5 and 15 degrees. Although they are generally not quite as effective as central air conditioners, evaporative coolers do have one major advantage in the fact that they continually bring a stream of fresh air into the room instead of simply recirculating the air already within the building.
There are numerous different types of evaporative coolers, some of which are meant to be mounted on the roof and others that are ground-mounted units. The majority of evaporative coolers are central units that only blow air directly into one room. However, these units can also be connected to the home's ductwork to circulate the cool air throughout the building.