Humidifiers: Indoor comfort

Choosing a humidifier involves trade-offs among efficiency, cost, noise, and convenience. Our tests also show that you can't tell how well a humidifier will work based on claims.

Who needs a humidifier? Anyone who suffers from uncomfortably dry or itchy eyes, throat, or skin, or whose asthma is a problem indoors during the heating season. Ideally, the indoor humidity should be 30 to 50 percent. In winter, however, that level can drop to 10 percent. That's because cooler air holds less moisture to begin with; when heated, its relative humidity drops even more.

Don't buy a humidifier, however, if you can't commit to cleaning and disinfecting it regularly, lest you end up with more problems from mold and mildew than you started with from dry air. (See Cleaning your humidifier.)

Humidifiers are better than in years past, when some models spewed white dust in our tests. But that does not mean they're all the same or work equally well.

New features

To make filling easier, manufacturers have added handles to the tanks and shaped them to fit underneath faucets. Nevertheless, portable humidifiers are somewhat cumbersome to fill and a pain to clean. (Another type, in-duct humidifiers, are plumbed into the water supply and drainpipes, so they don't need to be filled. Changing the filter, done once or twice a year, is simple.)

Some portable humidifiers can be programmed to turn on before you get home, so that your room will be at the right humidity when you arrive. But this convenience poses a problem: Water that just sits in the tank for hours can become a breeding ground for microbes if the humidifier isn't dried completely between uses.

Claims vs. reality

Several small tabletop models in our tests fell short of their claimed output, some models by 25 percent. That means they won't produce the claimed water vapor and may not bring up the humidity to the desired level. A few larger console models also failed to deliver the output their makers claimed, although it matters somewhat less because their overall output is much greater.

In some models, the humidistat, which controls humidity levels, was not always accurate. And most portable humidifiers won't let you set humidity levels below 30 percent. When outside temperatures drop below 20° F, even a 30 percent indoor humidity level can lead to window condensation. So you might not be able to run a humidifier when it gets that cold.