25" X 24" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 27 5/8" X 26 5/8"] Adjustable Return + Product Details Size - FG1836 HP-1 Product Details Size 20 ceiling

+ Product Details Size - 24"w X 26"h is the size for the duct opening measurement only

+ Product Details Size – 16"w X 28"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 12" x 24" or 24" x 12" duct opening (measured at the opening)

actual front end outer dimensions are approximately 26

+ Product Details Size - 16"w X 36"h is the size for the duct opening measurement only

25" X 24" Steel Return Air Filter Grille for 1" Filter Removable Frame [Outer Dimensions: 27 5 8" X 26 5 8"] Adjustable Return + Product Details Size FG1836 HP 1 Product Details Size 20 ceiling + Product Details Size 24"w X 26"h is the size for the duct opening measurement only + Product Details Size – 16"w X 28"h is the size for the duct opening measurement only