Hinged panel allows access to unit and return air filter. A field-supplied filter (25"x 20") should be mounted on the inside grille. Panel can be mounted with return air openings high or low on the door for optimum sound attenuation. Vert-I-Pak® Return Air Grille/Access Panel, Accessory Accessory, For Use With: Vert-I-Pak® Single Package Vertical Air Conditioner, 29 in W x 58 in H Dimensions, Domestic