A heat exchanger (5) includes a housing (31), which contains a tube (32) and has a jacket (33), which surrounds the tube (32) while forming a ring channel (34). A primary inlet (35) and a primary outlet (36) are fluidically connected with one another via a primary path (37) carrying a primary medium through the ring channel (34) and via a bypass path (38) carrying the primary medium through the tube (32). A control (39) controls the flow of the primary medium through the primary path (37) and through the bypass path (38). At least two secondary inlets (42) and two secondary outlets (43) are fluidically connected with one another via at least two secondary paths (44) for carrying at least one secondary medium. The primary path (37) is coupled with the secondary paths (44) in a heat-transferring manner and such that the media are separated from one another.