The invention concerns a heat exchanger with a large number of U-shaped tubes (3), preferably brought together to form at least one tubular bundle and arranged in a housing 2, and several partitions (4) subdividing the housing (2) into separate sections (5). For the formation of a heat exchanger which has a comparatively high efficiency even with increasing operation time, a heat exchanger is proposed in the invention that is characterized by at least one venting tube (6) that preferably extends through all sections (5) of the housing (2) and that has a number of venting holes (15) formed transversely to the longitudinal extension (14) of the tube.