Ventilation system for a residential building, said ventilation system comprising a heat exchanger, said heat exchanger comprising: - a beam-shaped housing wherein a first inlet, a second inlet, a first outlet, and a second outlet are provided, wherein the first inlet and the first outlet together are part of a first flow path and wherein the second inlet and second outlet together are part of a second flow path, wherein the housing is configured to be attached to a wall in the building via a first of its walls; - an air-to-air plate heat exchanger (44, 46) inside the housing and provided with a plurality of first channels that are part of the first flow path and a plurality of second channels that are part of the second flow path, wherein the air-to-air plate heat exchanger internally divides the beam-shaped housing in a first chamber and a second chamber; - a first drive unit, arranged for driving an airflow over the first flow path and a second drive unit arranged to drive an airflow over the second flow path; and - a condensation discharge tray positioned inside the housing and arranged for collecting condensation from the air-to-air plate heat exchanger, characterised in that the heat exchanger further comprises at least four condensation discharge openings (60a, 60b, 60c, 60d) in the housing, at least two of which are located in the first chamber and at least two of which are located in the second chamber, wherein one of the condensation discharge openings in the first chamber and one of the condensation discharge openings in the second chamber are located in opposing walls (12c, 12d) of the housing adjacent to said first wall and wherein the other of the condensation discharge openings in the first chamber and the other of the condensation discharge openings in the second chamber are located in the same wall of the housing which is adjacent to and extends from said first wall between said opposing walls, wherein the condensation discharge tray is arranged for draining the condensation to one of the condensation discharge openings. - a beam-shaped housing wherein a first inlet, a second inlet, a first outlet, and a second outlet are provided, wherein the first inlet and the first outlet together are part of a first flow path and wherein the second inlet and second outlet together are part of a second flow path, wherein the housing is configured to be attached to a wall in the building via a first of its walls; - an air-to-air plate heat exchanger (44, 46) inside the housing and provided with a plurality of first channels that are part of the first flow path and a plurality of second channels that are part of the second flow path, wherein the air-to-air plate heat exchanger internally divides the beam-shaped housing in a first chamber and a second chamber; - a first drive unit, arranged for driving an airflow over the first flow path and a second drive unit arranged to drive an airflow over the second flow path; and - a condensation discharge tray positioned inside the housing and arranged for collecting condensation from the air-to-air plate heat exchanger, characterised in that the heat exchanger further comprises at least four condensation discharge openings (60a, 60b, 60c, 60d) in the housing, at least two of which are located in the first chamber and at least two of which are located in the second chamber, wherein one of the condensation discharge openings in the first chamber and one of the condensation discharge openings in the second chamber are located in opposing walls (12c, 12d) of the housing adjacent to said first wall and wherein the other of the condensation discharge openings in the first chamber and the other of the condensation discharge openings in the second chamber are located in the same wall of the housing which is adjacent to and extends from said first wall between said opposing walls, wherein the condensation discharge tray is arranged for draining the condensation to one of the condensation discharge openings.