The device has housings (2, 4) that enclose a circulation chamber flow-throughable by a medium. Heating ribs are provided with a U-shaped recess. A positive temperature coefficient heating element (24) rests against opposite inner sides of the recess. The ribs are inwardly protruded downwards into the inner sides of the housings such that a flow passage of a meander-like flow channel is formed between free ends of the ribs and an inner wall of the housings. The flow channel is closed on a side opposite to a partition wall by a cover element (6).
