A thermal post-combustion unit with a combustion chamber having a combustion space to which exhaust air can be supplied, having a burner for heating the combustion space, whereby clean air is produced, having an inlet for exhaust air and having an outlet for clean air. A flow path connects the inlet to the combustion space. Exhaust air can be heated by a heat-exchanger system. The flow path comprises a first, second and third flow section, wherein the first flow section is connected to the inlet and the exhaust air flows from the third flow section to the combustion space, wherein the flow sections connect to one another at diversion ends so that the exhaust air flows through two successive flow sections with different flow directions. Heat-exchanger pipes extend at least inside the first and the second flow section or at least the first and the second flow section extend inside heat-exchanger pipes.