Abstract: A HEPA vent filter device comprising a housing having openings in front and back walls, a partition in said housing between said front and back walls positioned at an angle from vertical and defining a framed opening, extensible curtain walls on the exterior of said housing between said front and back walls, a HEPA filter, pivots mounting said HEPA filter for movement toward and away from said framed opening so that air passing through said housing in a first direction moves said HEPA filter away from said framed opening and air passing through said housing in the opposite direction moves said HEPA filter into engagement with said framed opening and a sealing gasket thereon.