Abstract: A vent device includes a vent frame and a fin arrangement. The vent frame includes a ventilating opening and a peripheral frame portion adapted for mounting at an air outlet of a heating and air conditioning system. The fin arrangement includes a plurality of vent fins longitudinally and rotatably supported at the ventilating opening, wherein each of the vent fins has first and second longitudinal sealing edges. When the vent fins are concurrently moved in an opened position, the vent fins are rotated to parallel with each other for allowing air passing through. When the vent fins are concurrently moved in a closed position, the first longitudinal sealing edge of each of the vent fins is overlappedly engaged with the second longitudinal sealing edge of the adjacent vent fin to completely seal the ventilating opening of the vent frame in an air sealing manner.