26" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Return Grille The first number in a

The first number in a grille size

For 10" duct opening

During summer

+ Product Details Size - 18"w X 18"h is the size for the duct opening measurement only

26" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Return Grille The first number in a+ Product Details Perfect Fit & Easy Sizing Designed for a 26" x 20" OR 20" x 26" duct opening (measured at the opening), with actual outer dimensions of 28. 5" W x 22. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 25. 75" x 19. 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