Getting started

Humidifiers use a fan to pull air over two sets of refrigerant-filled coils, one cool and the other warm, wringing out moisture along the way. All of the models we evaluated in our test chamber performed well overall. But some came much closer than others to the humidity levels we set on the humidistat. Some used less energy or ran more quietly. And a few had to be restarted manually after a simulated blackout.

Noise is a concern in living space. Our measurements from 4 feet ranged from 55 to 67 decibels for the models we tested. That's about the difference between the sound of loud conversation and the din of street traffic. Models with the smallest capacity tended to be the quietest, although one such model we tested was noisier than most larger units.

A dehumidifier can rack up more than $150 a year in electric bills. The largest-capacity humidifiers tend to be the most efficient, removing the most water for each kilowatt-hour used. Look for models with an Energy Star seal, which are 10 to 20 percent more efficient than non-Energy Star models.

New models appear in late spring and early summer, and most sales and in-store promotions occur from June through August. You might find closeout deals in the fall and early winter.

Even the best dehumidifier may not work effectively if too much outside moisture seeps into your home. Begin by checking that gutters aren't clogged and that downspouts are directing rainwater at least 3 feet away from the house. Grade your property so that rainwater flows away from the foundation. Keep the duct for your clothes dryer properly vented to the outside, making sure that it isn't clogged or leaking. Run an exhaust fan or open a window when showering, and squeegee or wipe down shower walls afterward. When cooking, use a range hood that vents outdoors.

In the basement, check the plumbing for leaks and condensation. For a damp rather than leaky basement, applying a waterproof coating (when walls are dry) may help. Use silicone caulk to seal small gaps in the foundation, and hydraulic cement for cracks. More extensive problems may require a sump pump, excavating and waterproofing exterior foundation walls, and installing drains outside.

Besides dehumidifiers, we also tested water-absorbing calcium-chloride crystals. The manufacturer of DampRid maintains that it will lower humidity to about 50 percent in spaces up to 1,000 square feet. Several small, refillable buckets or two large disposable ones cost about $26 to $28, so DampRid is a tempting alternative, especially for closets that lack the airflow needed for a dehumidifier. Just don't expect fast work. Even the large bucket removed less than 2 ounces of moisture over 24 hours in our test chamber, compared with 25 pints claimed for the smallest dehumidifier in our test group.

Types

Dehumidifiers vary according to how many pints of moisture they can remove in 24 hours. Here are the types of dehumidifiers to consider.

These models, rated at up to 75 pints per day, tend to be the most energy efficient. They can also handle a wider range of humidity levels with little or no additional noise. For large, wet spaces, buy the largest-capacity model you can afford. The modest extra cost is worth it.

These models are typically rated to remove 45 to 50 pints of moisture per day--adequate for medium-sized or large spaces that are damp rather than wet. While medium-capacity dehumidifiers can cost as much as large models, the best we tested still cost a bit less.

These can dehumidify small spaces that are damp rather than wet and are rated to remove as little as 25 pints of moisture a day. They also cost the least overall.

These are available as portable units or add-ons to your existing central-heating and air-conditioning system. Manufacturers say they can handle an area up to 3,000 square feet. These units are expensive, but the large amount of moisture they remove lets you run your air conditioner less.

Features

Most portable dehumidifiers come fairly similarly equipped, but a few special features are worth looking for. Here are the dehumidifier features to consider.

It should have comfortable handles and a cover that permits convenient removal and carrying when it's full. Capacities range from about 10 to 75 pints.

Electronic controls let you select a basic humidity level -- "normal", "dry", "very dry" -- while digital controls let you program a specific humidity with percentage numbers.

Most dehumidifiers have a sensor that turns off the dehumidifier if frost forms on the coils -- common in cooler spaces. That keeps the unit from wasting energy by running without dehumidifying.

If you place the dehumidifier in a basement with a floor drain, a hose connection lets you divert the condensed water directly to the drain so you don't have to empty the bucket. In a basement without a floor drain, a dehumidifier with a pump can send water up through the window or to a slop sink or other high drain.

This is more convenient than fiddling with the humidistat to turn the unit on or off.

A timer can program the unit to turn on and off while you're out of the house. It also can save money by turning on the dehumidifier at night, during cheaper off-peak electricity hours.

Look for one that's easy to clean.

This helps you to handle a heavier model.