Abstract: A panel air filter assembly, for use in heating, ventilating and air conditioning (HVAC) systems, which has a single filter element with multiple portions. The single filter element is sectioned into substantially equally-dimensioned and separate filter portions. Each of the filter portions includes a specific type of medium and is distinct from one another, so as to remove different types of contaminants from the outdoor supply air before entering heating, ventilating and air conditioning systems. A waterproof paperboard frame securely supports the filter element at the filter element's marginal edges.

Abstract: A panel air filter assembly, for use in heating, ventilating and air conditioning (HVAC) systems, which has a single filter element with multiple portions. The single filter element is sectioned into substantially equally-dimensioned and separate filter portions. Each of the filter portions includes a specific type of medium and is distinct from one another, so as to remove different types of contaminants from the outdoor supply air before entering heating, ventilating and air conditioning systems. A waterproof paperboard frame securely supports the filter element at the filter element's marginal edges.

Abstract: A filter window adapter unit adapted for use with a main split-sash window of school buses is provided. The adapter unit includes a mounting frame adapted to be installed over the main split-sash window of the school buses. An inner sash is disposed fixedly in a lower position in an inner track portion and carries a pane of glass. An outer sash is disposed movably in an outer track portion and carries an air filter. The outer sash is raised upwardly so as to cover a main window opening when the main split-sash is opened. As a result, the air filter prevents diesel fumes from the school buses from entering into the interior thereof.