Dehumidifiers take advantage of the phenomenon of condensation. Condensation occurs whenever a cold surface comes into contact with warmer, humid air. Some of the moisture in the air reverts to its liquid state and collects on the cold surface.
Example of Condensation
The most common example of condensation from everyday life is the buildup of water at the bottom of a glass of iced soda. The cold surface of the glass touches the hot, humid air around it, and some of the moisture from the air collects on the outside of the glass.
How Dehumidifiers Dehumidify
Inside the dehumidifier is a condenser coil. All the heat is pulled from the condenser coil, making it very cold. As the hot, humid air is pulled over the coil, some of its moisture condenses on the coil and drips into the bucket. The air leaves the dehumidifier with less moisture than it had before.
Since the coil must be colder than the air around it for the condensation to occur, the dehumidifier will ice over at surprisingly high temperatures. EnergyStar states that most residential dehumidifiers will begin to ice over if the ambient temperature drops below 65 degrees Fahrenheit.
Dehumidifiers designed to work in temperatures as low as 42 degrees are available. If dehumidifier freezing is a regular problem for your home, you may wish to invest in one of those models.