Suffering from the humidity? Chances are your basement is, too. Dampness and its accompanying side effects: mold, mildew, and condensation can create serious problems for your house and its occupants, including rot, peeling paint, and allergies. What's a homeowner to do? Consider the dehumidifier.
I first encountered a dehumidifier when my husband and I and our kids moved to London. Having lived on the West Coast all my life, humidity had never been part of my world. "You have damp." The words of doom from our contractor explained why the paint was flaking off the walls and ceiling of the underground office in our otherwise shipshape London abode. That's when I discovered that there's an entire industry devoted to damp proofing in London—and that a common case of damp, such as ours, can be rectified with a single appliance: a dehumidifier. We've since moved back to the West Coast, but I remain a dehumidifier devotee. Here's the lowdown on these contraptions:
What is a dehumidifier and how does it work?
A dehumidifier is a piece of equipment that reduces the humidity level in an enclosed space, whether a basement or room. It works by sucking in air, extracting the moisture, and then blowing out dry air via a fan. The collected water either drains into a removable basin contained in the dehumidifier or is released through a hose.
Buyer's tip: Most dehumidifiers have water pans that hold far less than the machine is rated for extracting from the air. There's typically an automatic shutoff when the basin is full, but for optimal functioning, it's wise to drain more often that you might think necessary. Alternatively, to prevent constant trips to empty the water pan, consider buying a model with permanent drainage (or the option to be rigged to a hose that runs into a nearby drain).
Above: An inside look at a condenser dehumidifier. (Learn about condensers below.) Image via Achoo Allergy.
Why use a dehumidifier?
Too much humidity inside can promote mold and mildew, cause condensation, and attract pests. The aftereffects can include allergy issues, and damage to the house itself and your possessions. And, then, of course, there's the comfort factor: dehumidifiers reduce the humidity indoors.
Humidity levels are measured by relative humidity. Translation: Depending on temperature, air can hold a set amount of water vapor; relative humidity is the ratio of actual vapor in the air to this set amount. The rule of thumb is that relative humidity in houses should range between 30 and 50 percent. Mold takes root when the relative humidity exceeds 68 percent. Many dehumidifiers and some central air conditioners have a built-in humidistat that tells the system to dehumidify the air to a desired point.
If you don't have a humidistat—most of us don't—signs that you may need to consider a dehumidifier include:
- Visible mold and mildew
- Condensation on windows
- Moisture on walls and fixtures
- Presence of silverfish and centipedes
- Peeling wallpaper or flaking paint
Basements in all parts of the country are especially prone to high humidity levels because the walls are surrounded by moist earth. When it comes to removing water flowing into a basement, you need a sump pump—see Gardenista's Hardscaping 101: Sump Pumps—but for controlling moist air, dehumidifiers are an effective tool (and they also work well in rooms beyond the basement in hot and humid climates.)
Above: Condensation on windows can result in swelling or rot of window frames and provide a perfect growing environment for molds.
Are there different types of dehumidifiers?
Dehumidifiers differ in their moisture extraction method as well as their installation type.
In terms of mechanics, the most common type of dehumidifier is a refrigerative or compressor machine. It removes the moisture using refrigerator coils to condense the air and collect the resulting water in a basin. Another type is the desiccative dehumidifier. It contains a filter or disc of silica gel-like material that absorbs moisture from the air as it passes through.
Dehumidifiers fall into two categories: portable or whole house systems:
Portable Dehumidifiers: Sometimes called single room dehumidifiers, portable dehumidifiers are stand-alone units that don't require professional installation. They come in a range of sizes and moisture-extraction capabilities, and are categorized by daily water extraction capacity or by the size of the space that needs dehumidifying (a figure often easier to estimate than moisture quantity). Other features to consider are a built-in humidistat, multiple fan speeds, internal condensate pump, and exterior finish that best suites your setting.
Whole House Dehumidifiers Integrated into an existing HVAC system, these large machines are able to dehumidify an entire house. They require professional installation, and, according to Consumer Reports, come with a pro and con: "these units are expensive, but the large amount of moisture they remove lets you run your air conditioner less." Manufacturers say whole house dehumidifiers can handle areas of up to 3,000 square feet. There are also specialty versions sized for crawlspaces and designed for indoor pools.
Above: I used a model similar to this compact Danby 30 pt. Dehumidifier ($179 at Amazon) to ward off the damp in my London basement office.
I have an air conditioner, doesn't it work as a dehumidifier?
The simple answer is yes, to a point. An air conditioner is not designed to remove humidity, but it does so as a byproduct of the cooling process. The air is condensed as it's cooled, eliminating some of the moisture. But in very humid environments, such as the South in August, the AC's dehumidification function may not be effective enough to keep the house at a safe and comfortable humidity level or to tackle a damp basement. In addition, air conditioners don't run all the time, so they're only sporadically beneficial. Cool mornings and the summer shoulder months don't require AC even though the air is full of moisture. Bottom line: in hot, humid climates, a supplemental dehumidifier is recommended.
Above: Many dehumidifiers are controlled by a device known as a humidistat that detects moisture in the air. It works much like a thermostat, automatically turning the dehumidifier on or off as needed based on the relative humidity percentage setting you choose. Image via National Geographic.
How best to maintain a dehumidifier?
The good news is that dehumidifiers require minimal care. The coils should be checked seasonally to be kept clear of dust and dirt. If the unit has a removable front cover, there may be a filter inside that should be cleaned—it's recommended that they be cleaned every six months to a year, depending on use. And be sure to drain the water bucket before putting the unit in storage for the winter.
Are there other ways to control humidity?
Yes, and it's wise to try other options first—to save electricity, reduce the need for yet another household appliance, and cut down on noise (dehumidifier fans and compressors are audible, especially when operating at high levels). Here are some ways to minimize interior humidity:
- Check your AC filter to be sure it's clean and not blocked.
- In hot and humid conditions, keep your house closed during the day. Ventilate at night naturally or with fans.
- Keep air circulating as much as possible (more fans!).
- Be sure you use exhaust fans when showering or bathing, and consider outdoor showers and cooking setups for summer houses.
- Take steps to keep your foundation dry by checking gutter drainage (it should be as far from the foundations as possible) and limiting perimeter plant watering.
- Be sure all moisture-producing appliances (such as dryers) are vented outside.
Above: A basement laundry room in Tokyo designed by Schemata Architects. Photograph via ArchDaily.
- Keeps relative humidity at optimal levels
- Prevents mold and mildew
- Prevents interior condensation
- Keeps moisture-loving pests away
- Portable units can be an eyesore (industrial designers, are you listening?)
Live in a dry environment? See Alexa's 10 Easy Pieces: Humidifiers. And if your basement moisture problem is beyond damp, Gardenista's Hardscaping 101: Sump Pumps might be your answer. Looking for remodeling advice? See all of our Remodeling 101 features.