A dehumidifier is the complete opposite of a humidifier and for that reason does not need a filter. It removes moisture from the air to lower the humidity level whereas a humidifier works to increase the humidity level.
Are Dehumidifiers Worth It – What Do You Think?
This is useful in climates that are often humid because excessive moisture in the air can cause problems such as mold growth, mildew, and dust mites. The most important benefit of a dehumidifier is the health benefits of maintaining the humidity level. The most preferable range is 30% to 50% relative humidity and most dehumidifiers have settings that allow the user to set a target humidity level.
The machine works much like an air conditioner but with both warm and cool coils. Cooled air holds less moisture so a fan blows the moist air over a cold coil which forces condensation of to form which is allowed to drip into a tank. Then the air is heated with the warm coil to the normal room temperature and released back into the room.
If the room is being cooled by an air conditioner then a dehumidifier is not needed since the very process of cooling the air is doing the dehumidifying. The only difference is that the dehumidifier warms the air which is not needed if the room needs air conditioning.
There are other strategies in dehumidifying air with various models of machines but typically the idea remains the same. Cool the air to force moisture out which serves the exact opposite purpose of a humidifier which attempts to release moisture into the air.