A heater with a housing with a fluid channel, disposed therein, with a fluid inlet and a fluid outlet, whereby a coil, which generates an alternating magnetic field and is separated sealed from the fluid channel by a coil housing, is provided in the housing, whereby furthermore at least one metallic flat heating element is provided, which can be heated by the alternating magnetic field. The at least one flat heating element is disposed in the fluid channel, whereby the fluid channel is divided at least into a first channel and a second channel. Walls bounding the channels are formed by the coil housing and/or by a flat heating element.