Abstract: An air filter cabinet designed for a relatively large electronic air filter cells is adapted to receive and position a relatively smaller filter element without an associated loose fitting relationship and air leakage. A plurality of S-shaped adaptor elements are each removably interconnected to a respective guide rail in the cabinet to reduce the size of a cavity so as to accommodate the smaller filter element and secure it in a fixed position while preventing air leakage therearound.

Abstract: A collapsible expandable air filter assembly includes an expandable pleated filter media, a filter frame made from a cardboard blank that is pre-scored, slit, creased and die cut to define a central area enabling air passage therethrough, and side and end panels foldable to positions generally normal to the central area to form a perimeter wall about the central area to receive and support the expanded air filter media. A filter grill is formed from a cardboard blank and has an open central area and laterally opposite marginal side and end walls foldable to enable mounting on the filter frame to assist in retaining the filter media within the filter frame. Separating fingers are formed integral with or separate from but connectable to the filter grill and are adopted to be positioned between adjacent expandable pleats to evenly position and secure the filter pleats.