Humidifier buying guide

These portable models cost the least and are fine for humidifying a single room, but their small tank requires frequent refills. Ultrasonic humidifiers use a vibrating nebulizer to emit water. Evaporative tabletops use a fan to blow air over a wet wick. Warm-mist models use a heating unit to boil water before cooling the steam. Impeller models produce mist using a rotating disk. Performance varies widely by type.

Although console models are larger than tabletops, they can still be moved from room to room. Whether evaporative or ultrasonic, console humidifiers generate lots of moist air. Since a console can humidify more than one room, it allows more options for unobtrusive placement wherever an electric outlet is available. A console's larger tank needs less frequent refills, but it's more cumbersome to handle. Evaporative models are louder than ultrasonic ones, so you may want to run this type of console for several hours until bedtime and then turn it off.

These humidifiers are the ideal choice if you have a forced-air heating system and want to humidify the whole house. They tap into the air ducts and are plumbed into the water supply. Most are evaporative-bypass units, which blow air over a wet wick. Some emit a warm mist. Others are nebulizers, which use a spray technology-and which may produce deposits of white dust from minerals in the water. In-duct humidifiers are quiet and require minimal maintenance. They're also the least expensive to run: about $30 or so per year, compared with as much as $350 or more for four tabletop models. But they generally require professional installation.

A tabletop or console humidifier should be easy to move and clean. The tank should fit easily beneath your bathroom faucet. (Some consoles have no tank. You need to fill them directly.) On evaporative models, the wick should be easy to replace. Look for user-friendly digital controls and displays of humidity level and settings.

Some humidifiers have a dial or digital humidistat that shuts off the unit when it reaches a preset humidity level. Models without a humidistat can raise the humidity enough to cause condensation on windows. Also, too much humidification can promote growth of mold, bacteria, and dust mites. If the humidifier doesn't have a humidistat, we recommend you buy a separate hygrometer that can monitor humidity levels in a space. Be aware that most humidifiers won't let you set the humidity below 30 percent, a level that can cause window condensation when outside temperatures drop below 20° F. That means you might not be able to use the humidifier when the weather turns very cold.

Ultrasonic humidifiers are quiet because they trade the usual fan for a vibrating nebulizer. Some warm-mist tabletop models make little or no noise beyond mild boiling and hissing sounds. Comparably sized evaporative models we tested emitted 45 to 50 decibels on their low setting and even more on their high setting. For large areas, consider buying a quiet ultrasonic console model. Alternatively, buy an evaporative model and place it away from sleeping areas. You'll spend less than you would on several warm-mist tabletop models, and the water vapor will travel quickly enough to benefit remote bedrooms if doors remain open.

You can program some tabletop and console models to turn on at a set time so that your room is at the right humidity when you get home. But this convenience might pose a problem: Water that sits in the tank for hours can breed microbes if you don't dry the humidifier thoroughly between uses.

Holmes humidifiers are equipped with the "Lifelong" feature (it is designed to filter out mineral deposits found in water), "AccuSet" digital humidistats (a preset humidity level), and "FilterCheck" (it monitors when filter needs changing). Holmes products are available at a wide variety of retailers, including Walmart, Target, and Kmart, and through Holmes' Web site. Prices range from $25 to $130.

Honeywell is available in a wide variety of discount stores as well as Target and Home Depot. They offer whole house and tabletop models. Prices range from $20 to $400.

Hunter was founded in 1886 and makes tabletop models that are available nationwide through Walmart, Target, Lowe's, and other mass merchants. Prices range from $50 to $150.

Kaz started in 1926 in upstate New York and remains a family-owned operation. The Honeywell trademark is used by Kaz under license from Honeywell. They offer tabletop units. Kaz humidifiers are available at such retailers as Walmart, Target, and Home Depot. Prices range from $15 to $120.