A waste heat recovery unit includes a duct for hot gas. The duct is divided into first, second and third adjacent and parallel channels each with an inlet and an outlet. A heat exchanger is located in each of the first and third channels. The second channel is located between the first and third channels and provides a bypass channel. A damper system is operable to selectively open and close the inlets of the three channels. This provides a more compact waste heat recovery unit configuration which is more straightforward to manufacture and maintain.