Abstract: An air duct has a filter mount opening originally intended to accept a shallow filter element for filtering air entering the duct. The opening has an interior flange whose original purpose was to support the shallow filter element. This flange has interior edges defining an air passage opening. The invention is implemented a filter unit including a frame and a deep filter element mounted in the frame. The frame has dimensions allowing the filter unit to replace the conventional shallow filter element with the frame inserted into the air passage opening and closely spaced to all of the interior edges. A resilient gasket is mounted adjacent to the opening's interior flange and projects slightly into the air passage opening so as to contact the deep filter element's frame. The gasket prevents air leakage between the interior flange's interior edges and the frame.

Abstract: A frame supports a deep filter element to allow the filter element to be installed in a duct's conventional air intake opening as a replacement for a conventional shallow filter element. The frame has a flange to mate with a surface of the intake opening's interior flange. In one embodiment, two identical side panels are assembled with the relatively stiff end panels of a particular filter element to form the frame.

Abstract: A filter assembly having first and second opposite frame members and a filter element removably secured to the first and second frame members is provided. The filter element is preferably a pleated paper filter, positioned in extension between opposite end panels. An arrangement is provided for securing the end panels to, and in extension between, the first and second opposite frame members. When the arrangement is assembled, an outer frame comprising the two frame members in the two end panels is provided. In the assembly, the pleated filter fills the area within the frame. The filter media can be conveniently removed and replaced in the frame, as desired.