The present invention relates to a damper door (1) having an axis of rotation (3), a first face (5), and a second face opposite the first face (5), said first (5) and second faces of the damper door (1) defining a plane, said damper door (1) comprising: a rotation shaft (9) projecting from each side of the plane defined by the first (5) and second faces of the damper door (1), and at least one side wall (11) having a flat surface arranged radially with respect to the rotation shaft (9), characterised in that the rotation shaft (9) has, in the plane of the at least one side wall (11), a semi-elliptical shape (13) extending over the side wall (11) and comprising a large diameter (G1) coinciding with the axis of rotation (3) of the damper door (1) and a small radius (P1) parallel to the plane of the at least one side wall (11).