How Dehumidifiers Work


Dehumidifiers can help prevent and, in some cases, repair damage to your home.
Dehumidifiers can help prevent and, in some cases, repair damage to your home.
© iStockphoto.com/Ceneri

If you live close to the equator or near a coastal region, you probably hear your local weatherman say the word "humidity" all too often. But no matter where you are, you've surely experienced it -- that muggy, heavy feeling that fills the air, often when it's rainy, foggy or hot outside. It can make your hair frizzy and may seem to dampen everything, including your mood.

When people complain about humidity, for the most part they're talking about relative humidity. Depending on temperature, air can hold a fixed amount of water vapor; relative humidity is the ratio of actual vapor in the air to this fixed amount. For example, at a temperature of 68 degrees Fahrenheit (20 degrees Celsius), one cubic meter (35 cubic feet) of air can hold about 18 grams (.6 ounces) of water. This would be a state of saturation, otherwise known as 100 percent relative humidity.

That's a lot of jargon to describe a level of humidity that, for many people, can feel extremely uncomfortable. When this humidity seeps into your home, it can make rooms feel stuffy and perhaps even smell musty. Beyond these superficial discomforts, too much humidity can have some more serious disadvantages, too. An overly humid home can lose its structural integrity, attract pests like silverfish and centipedes, and even make you sick.

In an average home in which the temperature is 68 degrees Fahrenheit, the relative humidity should ideally be between 30 and 50 percent. If you're struggling to reach that range, a dehumidifier may come in handy. Dehumidifiers remove excess moisture from the air, improving the comfort and health of your home.

In this article, you'll learn what types of dehumidifiers are available and how you can get the best results out of the dehumidifier you have. But first, read on to next page to find out exactly how a dehumidifier does its job.

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.

Types of Dehumidifiers

While refrigerative dehumidifiers may be the most well-known, desiccant dehumidifiers also do a great job of keeping a space nice and dry. True to their name, these dehumidifiers pull in air and pass it over a desiccant material such as silica gel. Desiccants naturally absorb moisture -- that's why you'll find little packets of silica gel in new shoes or electronic goods. Because desiccant dehumidifiers don't need to cool air before dehumidifying it, this technology is really ideal for sub-zero conditions.

Since the technology behind them is so simple and effective, dehumidifiers mostly vary in size and strength. Portable dehumidifiers are the kind that you usually see in the home improvement aisle; they're often plastic, relatively cheap and very lightweight. They're designed to be most effective in smaller spaces like a bedroom or kitchen. Restoration humidifiers are heavy-duty machines that can withstand harsh conditions -- they're usually used to repair heavy water damage caused by hurricanes or other natural disasters.

The largest models on the market, whole-house dehumidifiers, usually augment a home's existing heating, ventilating and air conditioning (HVAC) system. You'll have to hire a professional to install one of those. Some manufacturers have also created specially sized crawlspace dehumidifiers to address the humidity in storage areas and powerful dehumidifiers that are targeted toward the high humidity created by some indoor pools and spas.

Whichever kind of dehumidifier you choose, it may help make your home a little greener. Read on to find out how.

Using a Dehumidifier

You may be able to use greywater from a dehumidifier to water plants.
You may be able to use greywater from a dehumidifier to water plants.
© iStockphoto.com/VikaValter

A portable dehumidifier can consume 160 kilowatt hours per month (kWh) -- that's more than your refrigerator eats up. However, it does burn less energy than the average air conditioner, which tears through about 300 kWh per month. Also, since excessive relative humidity makes us perceive temperature as being higher than it is, keeping your home drier may lead you to reach for the thermostat less, which could result in lower energy consumption overall.

To really save on your utility bills and diminish your carbon footprint, work on maximizing your dehumidifier's efficiency. Don't keep it on all day, set the humidistat at a reasonable level (50 percent rather than 30 percent), and keep your doors and windows closed when it runs. Most dehumidifiers discharge air from the top of the machine, but if yours does not have top-mounted discharge, make sure that it's placed well away from walls and furniture to keep air circulating freely. Keep it away from sources of excessive dust or dirt, since this can very quickly clog the machine. For that matter, be sure to check and clean your dehumidifier's filter regularly -- this will help ensure that it's operating as efficiently as possible.

In addition to saving energy, you also might be able to recycle the water that your dehumidifier collects. The water that shows up in your dehumidifier's bucket is considered greywater. That means it's not suitable for drinking, but can be great for watering houseplants and flowers, since it's less salty than tap water. However, you should check first to see if there are any restrictions on using greywater in your area.

While the benefits of dehumidifier ownership are many, there are some potential downsides, too. For one thing, cost may be an issue. Dehumidifiers can be somewhat pricey -- many models sell for more than $150. Or you may just object to having a bucket of standing water sitting around in your home. No matter what your reservations are, it's worth figuring out if you really need a dehumidifier before you take the plunge and buy one. Read on for some tips that may help you make that decision.

Do you need a dehumidifier?

Start by taking a look around your home. The most noticeable symptoms of excessive humidity may include wet stains on your walls and ceilings, rotting and weakened wood, mold and fungus, condensation on your windows, peeling wallpaper, blistering paint, and a generally musty, stuffy feeling.

In addition to those somewhat obvious signs of humidity, there are also some more subtle conditions you can watch out for. For example, you may want to look into a purchasing a dehumidifier if your doors, cabinets or windows are sticking, or if your floors are especially creaky. When wood absorbs moisture, it swells. This pushes apart joints, loosens screws and nails, and generally compromises your home's strength. While your noisy stairs might be a simple nuisance now, if humidity is the underlying issue, your problems could get worse.

Dehumidifiers can also help mitigate the effects of common allergies to dust mites, fungus and mold; if the air in your home is excessively moist, it can encourage the growth of these allergens.

Even if you don't have allergies, preventing mold growth is a good reason to consider getting a dehumidifier. Mold only requires a bit of moisture to grow, and it can set up shop in your home as soon as one of its airborne spores finds a hospitably damp surface. A mold problem in your home can cause serious illness. And once it shows up, mold is a pain to eradicate and can permanently stain or damage whatever it's decided to live on. The easiest strategy is to just keep it from showing up at all.

You can also use a dehumidifier to discourage insects from moving in with you. Roaches, silverfish, spiders and centipedes all love a moist environment. Keeping the air in your home relatively dry will drive away those unwanted tenants. Additionally, if you've got a cold or a particularly bad, congested cough, using a dehumidifier may free up your breathing and help you sleep better at night.

As you can see, there are plenty of good reasons why you might consider using a dehumidifier. To find out more about these devices and related topics, follow the links on the next page.

Related HowStuffWorks Articles

Sources

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