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How Dehumidifiers Work

Dehumidifier Basics

Imagine enjoying a soda during a particularly warm day. When you pick up the can, you might notice that it's wet -- there's moisture on the outside. Why is that? As air loses heat, it also begins to lose its ability to retain moisture; the colder surface pulls and collects water from the warmer air, creating condensation. Your dehumidifier does pretty much the same thing. Most dehumidifiers can be broken down into five component parts:

  • Fan Compressor -- This compresses and expands a refrigerant gas like freon to cool the dehumidifier's coils. (See How Air Conditioners Work for a more detailed explanation of this cycle.)
  • Reheater -- This captures and collects heat that the cooling process generates.
  • Compressor cooling coils
  • Reservoir

How do all these parts fit together to pull moisture from the air? It's fairly simple, but very effective:

  1. A fan collects air from the surrounding area and pulls it into the dehumidifier.
  2. As the air passes through, it comes into contact with the dehumidifier's cooled coils. These coils use condensation to pull moisture from the air. The collected moisture remains on the coils and drips into the dehumidifier's reservoir.
  3. The dehumidifier reheats the air and exhausts it back into the room.

A dehumidifier usually has a removable plastic bucket for a reservoir; most buckets also have a place where you can hook up a hose so the collected water can drain straight into a floor drain or pump. This frees you from having to remember to dump out the water. But don't worry too much about the reservoir overflowing -- most dehumidifiers also have an automatic shut-off. If you're using a dehumidifier in extremely moist conditions, however, or if you need to keep your dehumidifier on all the time, you should look into a unit with a built-in condensate pump, which regularly pumps water out of the unit's reservoir rather than simply relying on gravity to empty it as a hose does.

Many dehumidifiers also have a humidistat, which allows you to set your desired level of relative humidity. A humidistat has two parts: a sensing element and a relay amplifier. The sensing element includes two alternate metal conductors, and changes in relative humidity will cause electrical resistance between those conductors. The relay amplifier measures this resistance and sends a signal to turn the dehumidifier on or off. These basic components add up to a device that may make your home feel a whole lot better.

Now that you know the basics of dehumidifier technology, it's time to learn about different kinds of dehumidifiers. Which one may be right for you? Read on to find out.