A heating device for heating a yarn, in particular in a texturing machine. The heating device comprises a thin-walled heating tube, which can be evenly heated on its circumference by a heating jacket. Fitted within the peripheral wall of the heating tube is an insert, which forms a yarn channel extending between a yarn inlet and a yarn outlet for guiding the yarn. The insert is formed by a special section rail that is open along one long side, and fitted with its opposite long side to the wall of the heating tube. As a result, the yarn channel is formed between the open long side of the special section rail and the wall of the heating tube, so that it is possible to supply heat to the yarn channel directly via the wall of the heating tube.