Abstract: A humidifying device automatically controllable to discharge an abundant supply of steam into the outlet or plenum chamber of an associated air handling apparatus such as a forced air furnace in a home or other structure to provide and maintain a desired preselected humidity condition, which device includes a tank having a chamber for holding a supply of water to be vaporized, said tank having an inlet into said chamber through which water can flow, a valve associated with said inlet for regulating the inlet water flow and a conduit for connecting said valve to a source of water, a probe member mounted on the tank and extending downwardly therein from an upper location, a heating element extending into said chamber near the bottom thereof, a steam outlet near the top of the tank through which steam produced in the chamber can escape, a second conduit having one end connected to the steam outlet and an opposite open end for connection to the plenum chamber of the furnace in position to discharge steam from sai