A vent assembly for a ventilation duct, for example a controlled domestic ventilation (CDV) ventilation system, comprising: • a frame that is insertable into the ventilation duct, is connectable to the latter in operationally durable manner, and surrounds an air passage, and • a cover element provided with at least one passage opening, the cover element and the frame being elements that are constructed separately from one another and are fastenable to one another, the vent assembly furthermore comprising at least one permanent magnet , and at least one fastening surface for the at least one permanent magnet being provided on the cover element, which permanent magnet can be brought into magnetic retention engagement with at least one mating surface provided on the frame , characterised in that the at least one permanent magnet and the at least one mating surface are dimensioned such that the cover element is displaceable relative to the frame when in magnetic retention engagement, in that the frame has a substantially flat end face that at least partially surrounds the air passage, in that the height of the at least one permanent magnet is substantially identical to the distance from one edge of the end face to the at least one mating surface , in that the at least one mating surface is integrally connected to the frame , in that the cover element is substantially level, and in that, in the event of the at least one permanent magnet and the at least one mating surface being arranged within the end face that at least partially surrounds the air passage, displacement of the cover element is limited by at least the at least one permanent magnet resting against an inner edge that bounds the end face . • a frame that is insertable into the ventilation duct, is connectable to the latter in operationally durable manner, and surrounds an air passage, and • a cover element provided with at least one passage opening, the cover element and the frame being elements that are constructed separately from one another and are fastenable to one another, the vent assembly furthermore comprising at least one permanent magnet , and at least one fastening surface for the at least one permanent magnet being provided on the cover element, which permanent magnet can be brought into magnetic retention engagement with at least one mating surface provided on the frame , characterised in that the at least one permanent magnet and the at least one mating surface are dimensioned such that the cover element is displaceable relative to the frame when in magnetic retention engagement, in that the frame has a substantially flat end face that at least partially surrounds the air passage, in that the height of the at least one permanent magnet is substantially identical to the distance from one edge of the end face to the at least one mating surface , in that the at least one mating surface is integrally connected to the frame , in that the cover element is substantially level, and in that, in the event of the at least one permanent magnet and the at least one mating surface being arranged within the end face that at least partially surrounds the air passage, displacement of the cover element is limited by at least the at least one permanent magnet resting against an inner edge that bounds the end face . <EOS>