Abstract: An add-on humidifier kit for use with a room air conditioner includes a cabinet frame extension for mounting on the room-side of the cabinet sleeve. The extension is composed of an upper water distribution header and a lower drain trough retaining a water pad located in an extension of the discharge duct of the air conditioner, while an electrical heating unit is mounted in the extension to heat the return room air to achieve a comfortable temperature, allowing the heated air to pick up moisture from the water pad. A portable water tank assembly is adapted to be positioned on the floor beneath the air conditioner and electrically coupled to the air conditioner through separable connectors providing tank mounted controls for the heating unit along with a humidistat, water flow regulator and water pump mounted in the water tank unit.