Grille filters are used in the return air vents, grilles of walls, and ceilings. There should be at least a 7-in depth behind the grille. This will provide enough space for installation and airflow through the filter. Grille filters provide greater airflow and efficiency due to the increased surface area and depth compared to standard 1-in filters. We recommend changing the filters every 6-12 months depending on environmental factors. Available in several sizes below!