How Does a Furnace Humidifier Work?

Furnace Humidifer Basics

The furnace humidifier is generally attached between the hot air duct flowing into the house and the cold air return bringing air to the furnace. A portion of the hot air is channeled into the humidifier, where it picks up droplets of water. It is then fed back into the cold air return, which flows into the furnace, heating it again. This heat completely vaporizes the water droplets so that they are absorbed by the hot air.

Disk Wheel and Drum Humidifiers

In disk wheel and drum-style humidifiers, a rotating wheel carries water from a tray to an air stream. In drum-style humidifiers, the water is picked up by absorbent pads. Air blows past the pads, absorbing water as it passes. Disk wheels use many small plastic disks instead of pads. Each plastic disk only holds a bit of water, but together they have enough surface area to hold quite a lot. Because of the size of the surface area, the hot air can absorb water very efficiently.

Flow-Through Humidifiers

Flow-through humidifiers have no flow parts. Instead, they have a small, porous aluminum device known as a biscuit. Water flows through a nozzle in the biscuit, and air blows through the side. Because of all of the holes in the biscuit, there is a lot of surface area for the water to cover. This allows the air to absorb water vapor very efficiently.