Grille filters are used in the return air vents and grilles of walls and ceilings that have at least a 7-in. depth behind the grille to provide enough space for installation and airflow through the filter. Grille filters provide a much higher rate of airflow and greater efficiency because of the increased surface area and depth of the media compared to a standard 1-in. filter. Recommended change is every 6-12 months depending on environmental factors. Available in several sizes below!