Return Air Filter Grille, Fits W50.5 x H50.5cm Duct Opening Size, Filter Included, Return Air Vent Cover for Wall, Powder-Coated Steel Return Air Grill Detachable Face/Door for 1 inch FiltersProduct Features How to Measure Before installation, measure the wall opening to determine the correct size to order. Wall opening size equals the listed dimensions. For example, if the pipe opening on the wall is 20 inches wide by 20 inches high, please order the 20 x 20 size option. Efficient Airflow This wall return air grille provides a quiet and efficient ventilation experience for your heating and cooling system. The angled fin design maximizes