20" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 10in diameter + Product Details Perfect Fit

+ Product Details Perfect Fit & Easy Sizing - Designed for a 34" x 36" OR 36" x 34" duct opening (measured at the opening)

And The Cooler Air From Outside WIll Flow In From The Bottom

[Outer Dimensions: 50

+ Product Details Size - 12"w X 30"h is the size for the duct opening measurement only

20" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 10in diameter + Product Details Perfect Fit+ Product Details Perfect Fit & Easy Sizing Designed for a 20" x 18" OR 18" x 20" duct opening (measured at the opening), with actual outer dimensions of 22. 5" W x 20. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 19. 75" x 17. 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