A heating device for the vaporization of active substances, such as air freshener fragrances, disinfectants, sanitizing agents, insecticides and the like, in which a wick is immersed in a fluid active substance and heat is applied to produce vaporization. The heating is produced by one or more electrical resistance elements embedded in a circular heating ring which is hinged to move over the end of the wick and encircle it. The internal wires which carry electrical current from a source of electrical power are led through the hinged area for connection to the electrical resistance elements, and a feature of the invention is the protection of such wires as they pass through the hinged area.