Choosing a dehumidifier requires the consumer to consider the size of the room and the humidity level. Manufacturers rate dehumidifiers by the number of pints of water they remove from a room in a 24-hour period.
While a 10-pint unit is sufficient for a moderately damp 500 square foot room, a 2,500 square foot room where the owner hangs laundry to dry requires a 44-pint unit. In most cases, the goal is to reduce the humidity level to between 30 and 50 percent. With a relative humidity in this range, mold and mildew are less likely to grow.
Many dehumidifiers have a receptacle to collect water. On units without a drain connection, the owner must remove the container several times daily to empty it. Dehumidifiers usually have a switch that turns off the unit before the container overflows. Units with the drain connection allow the water to flow into a floor drain or have a pump to lift it to a sink, eliminating the need to remove the receptacle.
Manufacturers measure the energy efficiency of a dehumidifier using the energy factor. They determine this factor by dividing the number of liters of water the machine removes from the air by the number of kilowatt-hours of electricity it uses. The most efficient machines have the highest energy factor.