36" x 14" Cube Core Eggcrate Return Air Filter Grille for 1" Filter return filter + Product Details Size -

+ Product Details Size - 30"w X 26"h is the size for the duct opening measurement only

40"w X 16"h Is The Size For The Duct Opening Measurement Only

The total outer size of this grille is the listed size plus 1

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+ Product Details Perfect Fit & Easy Sizing - Designed for a 28" x 36" OR 36" x 28" duct opening (measured at the opening)

36" x 14" Cube Core Eggcrate Return Air Filter Grille for 1" Filter return filter + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 36" x 14" OR 14" x 36" duct opening (measured at the opening), with actual outer dimensions of 38. 5" W x 16. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 35. 75" x 13. 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