Patent ID: 7708795

Claim:
An air filter unit having a shape of a tube, comprising: a top plate having an air inlet leading into an interior of the tube; two concentric cylindrical, air permeable tubes; and a bottom plate, wherein a space between the two concentric tubes is filled with filter media, and a sealing ring of a resilient material is surrounding the air inlet in the top plate, the top plate includes at least one protrusion on a side thereof facing a wall in use, a height of said protrusion being less than a distance with which the sealing ring, when not subjected to load, projects out from a surface of the top plate, and the top plate includes fasteners for removably attaching said air filter unit to the wall so that the air inlet of the top plate is concentrically disposed in relation to an opening in said wall and so that said at least one protrusion abuts said wall when the air filter unit is attached thereto, and in that an inner tube of the two tubes is shorter than an outer tube of the two tubes.