Air filter unit for sliding sash windows

Claim 1

A filter unit to be fitted in the frame of a sliding sash window between the sash and the bottom or the top of the frame, comprising a central member of substantially rectangular cross section, two end members of substantially rectangular cross section, each of said end members being dimensioned to receive and slidably fit over an adjacent end of the central member; each of said end members having front and rear walls and upper and lower edges, said upper and lower edges lying over upper and lower edges of the central member; ventilating apertures in front and rear walls of the central member through which air can flow through said central member, a filter pad in the central member through which said air must flow, said central member having a vertical slot in the rear wall thereof through which said filter pad can be inserted and removed from the central member, an air impervious sheet removably mounted in the central member extending longitudinally thereof and between the apertures of the front and rear walls selectively to prevent air from flowing therethrough, an end portion of said impervious sheet normally projecting through said vertical slot and by means of which the sheet can be grasped and partially or completely withdrawn through said vertical slot, and filler strips on and extending the length of said upper and lower edges of the central member and having outer surfaces facing away from the central member, said upper and lower edges of the end members having slots therein to accommodate the filler strips of the central member, the outer surfaces of said filler strips and the upper and lower edges of the end members being in upper and lower common planes and forming continuous upper and lower edges for said filter unit and extending the full length thereof whereby, when said unit is placed between a window sash and the frame thereof, there is no space between the sash and the frame of air to flow through.