18" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Color_Red Oak Wood + Product Details Perfect Fit FG1836 HP-1 Product Details Size 20 ceiling

+ Product Details Perfect Fit & Easy Sizing - Designed for a 36" x 14" OR 14" x 36" duct opening (measured at the opening)

Actual Filter Size – 25 3/4"w x 17 3/4" x 1"

The integrated eight-tumbler lock system

+ Product Details Perfect Fit & Easy Sizing - Designed for a 20" x 36" OR 36" x 20" duct opening (measured at the opening)

+ Product Details Size – 20"w X 30"h is the size for the duct opening measurement only

18" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Color_Red Oak Wood + Product Details Perfect Fit FG1836 HP 1 Product Details Size 20 ceiling + Product Details Perfect Fit & Easy Sizing Designed for a 36" x 14" OR 14" x 36" duct opening (measured at the opening) Actual Filter Size – 25 3 4"w x 17 3 4" x 1"