Evaporative humidifiers capture minerals and pollutants from water, providing clean vapor. These work by passing an air stream through a wet medium, such as a sponge or dampened grill.
Some have fiber honeycomb-type panels that wick water upward from a reservoir; others employ a foam or cloth drum that spins through a water-filled trough as air passes by. Still others blow air through a woven aluminum pad that is saturated by a constant stream of water. In some cases, filters are treated with a special compound that retards bacterial growth.
Central evaporative humidifiers like the one shown here are attached to the home heating system. Their output capacities range up to 25 gallons of water per day. High-capacity models are fan powered; the others don't require a motor. All are hooked up directly to the plumbing so manual filling isn't needed.
--Don Vandervort
