Determine if you need a desiccant (passive unit) or mechanical dehumidifier (active unit). The desiccant model uses a desiccative material to take water vapor out of the air. This type of unit is inexpensive and simple. The mechanical dehumidifier is the most commonly used dehumidifier. It can be considered an air conditioner as it takes the air from the room and circulates the air over cold coils, removing the water to be held in a bucket in the unit. Because of its ability to cool the air as it removes the humidity, a mechanical dehumidifier is preferred over the desiccant type.
Choose a dehumidifier that has either a compressor or a thermo-electric peltier. If you have a small room with a lot of moisture, you may want a thermo-electric peltier unit, which emits no noise or vibration, uses no compressor and has no refrigerant. This type of technology is great for closets, very small rooms or campers because the unit uses a heat pump to move the air over a temperature gradient, which cools or heats the air as it removes the water vapor. Compressor units are good for larger rooms and basements. As the air is moved over the cooling elements, the water is deposited into the holding bucket. However, the fan-and-compressor units do make some noise.
Consider the size and portability of the unit before purchasing. Use the guide (see Reference) to determine what size unit you need. Look for a unit that has casters or a handle for moving the unit to different rooms. A 60-pint capacity unit can weigh about 55 pounds, so casters would make it easier to move.
Check to see if the dehumidifier has an automatic shutoff and a built-in humidistat. The humidistat allows you to adjust for different humidity levels and the automatic shutoff will prevent the water-holding bucket from over filling.
Look for a dehumidifier that has a removable, washable air filter. This saves on maintenance. You simply remove the filter, wash it and replace it.
Check the water storage tank capacity and look for a unit with a continuous drainage system if you do not want to empty the water-holding bucket every day. To use a continuous drainage system, you must place the unit near a drain.