The invention relates to a heating device (9), for a mobile inhalation unit for the inhalation of active agents, comprising a heating wire (15), with two connector ends (23, 31) for the introduction of electrical energy and a thermal reservoir (13, 17) for heating air flowing along the thermal reservoir, whereby the thermal reservoir may be heated by means of the heating wire. The heating wire has a temperature coefficient of at least 0.001 K−1. The invention further relates to an inhalation unit with such a heating device and a method for heating a thermal reservoir on such a heating device.