Abstract: A ventilation unit (1) is formed by at least one fan (2), a heat exchanger, axially spaced from the fan (2), and a housing (3). The housing (3) has a first housing section (4), with a constant flow cross-section, where the heat exchanger is arranged. A second housing section (5) adjoins the first section (4) in the axial flow direction. The fan (2) is arranged on the second housing section (5) in the axial flow direction. During operation, the fan conveys air through the heat exchanger, arranged in the first housing section (4), and through the second housing section (5). The flow cross-section of the second housing section (5) is reduced in the flow direction from the first housing section (4) to the fan (2) by an adaptation to the form of housing wall sections (6, 6?) of the second housing section (5).