Abstract: An ultrasonic humidifier system which is mounted to an air duct of a heating system. A vibrator excites water within a reservoir so as to create a fog within a fog chamber. A panel directs air flow from an upstream furnace into the fog chamber for interaction of the air flow with the fog. This interaction increases the moisture content of the air flow so as to increase the humidity level thereof. Reed switches are provided to preclude vibration if the level within the reservoir is low and/or if no air stream is delivered from the furnace.