Dry winter air can result in cracked skin, gaps in your floorboards, and ashy furniture.

Every winter, humidifiers seem to pop up everywhere. Stacked on store shelves, spotlighted in home-care roundups and quietly humming in bedrooms across the country. And it’s not hard to understand why ...

But humidifiers are more complicated to use and care for than some other household appliances—and doing so incorrectly can be ...