Abstract: The specification discloses a humidifier for connection to a hot gas furnace having gas burners for heating air to be discharged through a plenum chamber and having a hot waste gas vent pipe for venting heated waste gas. The humidifier includes a housing which is substituted for a section of the hot waste gas vent pipe. A coil is disposed within the housing for directing water through the hot waste gas vent pipe so that the coil is heated from ambient temperature to a predetermined operating temperature by the waste gas thereby vaporizing the water into steam. The coil material has a substantial coefficient of thermal expansion so that the coil substantially expands and contracts as its temperature changes thereby separating sediment from the interior thereof. The coil has an inside dimension larger than the cross-sectional dimension of the vent pipe so that the flow of hot gases through the housing is not inhibited by the coil.

Abstract: A humidifier includes an electric heating coil and a water receiving/steam generating coil both positioned in a steam generation zone of a housing. The heating coil functions to vaporize water flowing through the water receiving/steam generating coil into steam by raising the temperature within the steam generation zone to an operating temperature which is sufficiently high to kill bacteria entering the humidifier with the water. The water receiving/steam generating coil is formed from a material having substantial thermal expansion characteristics whereby the coil substantially expands as the temperature within the steam generation zone is raised and substantially contracts as the steam generation zone cools. The expansions and contractions of the coil dislodge sediment tending to form therein, and the sediment is flushed from the coil by the fluid flowing therethrough.