Abstract: An HVAC air filter having a frame is disclosed. The frame disclosed includes filtration media and corners designed to allow for the expansion of the frame. The expansion of the frame allows for full nesting of multiple air filters.

Abstract: An HVAC air filter having a frame is disclosed. The frame disclosed includes filtration media and corners designed to allow for the expansion of the frame. The expansion of the frame allows for full nesting of multiple air filters.

Abstract: A planar frame of cardboard or other suitable sheet material with an interlocking corner construction. The corner connection provided in this invention securely locks the corner in place at low manufacturing cost. It can be integrated easily into the filter frame assembly process without addition additional steps. While the locking mechanism is secure to hold the frame in place for transport, during manufacturing, and for final filter usage, it is removable to allow for the frame to be unfolded and reassembled if necessary during manufacturing, e.g. to insert filter media. Preferably, after inserting filer media, the tabs hold the filter and frame in an assembled configuration until the frame can be sealed with adhesive. In a preferred embodiment, the frame comprises three simple, rectangular tabs. The first tab is attached to the first frame leg and simply slides between the outer and inner frame parts of the second frame leg. The second tab, which is small in width (approx.