It can also cause condensation that can disrupt sleeping, or prevent laundry from drying thoroughly enough to prevent mustiness. Higher humidity is also preferred by most pests, including clothes moths, fleas, cockroaches, woodlice and dust mites. Relative humidity in dwellings is preferably 30 to 50 percent.
By their operation, dehumidifiers produce an excess of water which has been removed from the conditioned air. This water, usually called condensate in its liquid form, must be collected and disposed of. Some dehumidifier designs dispose of excess water in a vapor, rather than liquid form. Energy efficiency of dehumidification processes can vary widely.
Dehumidifiers are also used in industrial climatic chambers, to control relative humidity within certain rooms to stay at levels conducive to processing of products.
> Thermal condensation
These methods rely on drawing air across a thermocline. Since the saturation vapour pressure of water decreases with decreasing temperature, the water in the air condenses on the cold surface, and is separated from it.
Most portable dehumidifiers are equipped with a condensate collection receptacle, typically with a float sensor to detect when the collection vessel is full, to shut off the dehumidifier and prevent an overflow of collected water. In humid environments, these buckets will generally fill with water in 8–12 hours, and may need to be manually emptied and replaced several times per day to ensure continued operation.
Many portable dehumidifiers can also be adapted to connect the condensate drip output directly to a drain via an ordinary garden hose. Some dehumidifier model can tie into plumbing drains or use a built-in water pump to empty themselves as they collect moisture. Alternately, a separate "condensate pump" may be used to move collect water to a disposal location when gravity drainage is not possible.