Sometimes your household air is too dry and you need to add moisture.
Sometimes your air is too soggy and you need to subtract some moisture.

What is a DEhumidifier?

A dehumidifier is a device to strain some of the excess water out of the surrounding air.
If you have an air conditioner, you already have a dehumidifier.

Dedicated dehumidifiers work on the same principle as an air conditioner.
Much like air conditioners, they also come in whole-house and room versions.

You set a dehumidistat (which is the same device as a humidistat, only it’s attached to a dehumidifier rather than to a humidifier), and it detects when the local air is at a higher relative humidity than the current setting. When that happens, the dehumidistat causes the dehumidifier to begin working. When the relative humidity of the air drops to the level on the control, the dehumidistat causes the dehumidifier to stop working.

How does a dehumidifier work?

As we said, it works pretty-much like an air conditioner – a compressor compresses some refrigerant, the refrigerant is run through an evaporator coil or radiator, where it expands rapidly, sucking the heat out of the radiator, which sucks the heat out of any air that touches it. A fan blows air across that radiator. As the air cools, it loses its ability to hold water, and the water is either collected in a bucket or directed down a drain.

A portable dehumidifier unit can be wheeled to any room in the house. It doesn’t chill the room where it’s working, because while one side of it is being made cold, to precipitate water from the air, the other side of the same unit is spilling the compressor heat into the same room. On average, the room heats up a bit.

You could do basically the same thing by running a window-mount air conditioner in the middle of a room, rather than in a window. When it’s mounted in a window, the compressor heat gets exhausted to the outdoors, while the radiator coil faces indoors. A fan keeps room air moving across the coil. Any water that precipitates out of the indoor air is directed outside by a short hose or pipe.

Again – just to reinforce the notion that it’s all the same technology, just tweaked for a particular purpose, think of your car’s climate-control system. If you live in Texas, you won’t have much experience with this part, but if you live in Ottawa, Canada (or even Ottawa, Illinois, we suppose…) then in the cold days of winter your car windows get frosty. You can run your heater to slowly get rid of the frost, but it actually works faster in the “Defrost” setting, which uses your car’s air conditioner to dry the air. The “Defrost” setting blows the driest possible air onto your windshield and your side windows, and none of it at your feet. The frost clears quickly.

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