18" x 26" or 26" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Compatible With Duct 12in order a 20x14 grille

order a 20x14 grille

then you'll need a 14-inch round vent

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

easy unrestricted airflow

+ Product Details Size - 32"w X 8"h is the size for the duct opening measurement only

18" x 26" or 26" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Compatible With Duct 12in order a 20x14 grille+ Product Details Perfect Fit & Easy Sizing Designed for a 18" x 26" OR 26" x 18" duct opening (measured at the opening), with actual outer dimensions of 20. 5" W x 28. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 17. 75" x 27. 75" x 1" Premium Airflow Efficiency High performance cube core eggcrate design allows 95% airflow efficiency, reducing energy costs and maximizing HVAC system lifespan. Durable, Rust Free Aluminum