18" x 20" or 20" x 18" Cube Core Eggcrate Return Air Grille 1-Way + Product Details Size –

+ Product Details Size – 24"w X 28"h is the size for the duct opening measurement only

+ Product Details Outer dimensions: – fits a duct opening

+ Product Details Size - 24"w X 4"h is the size for the duct opening measurement only

+ Product Description Upgrade your HVAC system with our 8" Round Air Vent Supply Grille

18" x 20" or 20" x 18" Cube Core Eggcrate Return Air Grille 1-Way + Product Details Size –+ Product Details Size 18" x 20" or 20" x 18" is the size for the duct opening measurement only, actual front end outer dimensions are approximately 19. 75" X 21. 75". High Quality High quality, rust free aluminum construction with smooth finished edges and counter sunk screw holes (screws included); no sharp edges.. Installation Location sidewall and ceiling. Design Cubic core eggcrate design Offers highest airflow efficiency at almost 95%, reducing