Abstract: An air filtering unit includes a generally rigid, affixed framework having an inwardly extending planar flange defining an opening. A box-like filter cartridge has a lower edge surface adapted to seat on the framework flange. Means are provided for securing the filter cartridge in position on the framework. Such securing means include at least two opposing adjustable fastening means, each of which includes an elongated strap attached to its lower end to an outer wall portion of the framework and extending outwardly a distance greater than the height of the filter cartridge. A bracket, having a slot which matches the strap so as to be slidable thereon, is mounted on the strap and adjustable means are mounted on the strap outwardly of the bracket and movable along the strap into forcing engagement with the bracket to urge the filter into engagement with the framework.