This sub-assembly directs the exhaust air away from the heat exchanger. The by-pass has a very large area and it operates very effectively. Its operation is controlled by means of temperature sensors placed inside the recuperator. It guarantees optimal air parameters in the transient periods (spring, autumn) and in the summer season it allows to cool the air down in the rooms at night. Do you know that in the summer your air handling unit can cool your house down? The by-pass is used in the summer season when heat recovery is not required. It consists in removing the heat exchanger and mounting a by-pass in its place. It allows for increasing the airflow and it guarantees cooling on hot days.