28" x 12" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w26h26 Ideal for Walls & Ceilings:

Ideal for Walls & Ceilings: Designed for seamless installation in standard 18" X 12" duct openings

With a 8" diameter for the duct opening measurement

+ Product Details Size – 22" x 26" or 26" x 22" is the size for the duct opening measurement only

Actual Filter Size – 25 3/4"w x 21 3/4" x 1"

+ Product Details Size – 16"w X 28"h is the size for the duct opening measurement only

28" x 12" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w26h26 Ideal for Walls & Ceilings:+ Product Details Perfect Fit & Easy Sizing Designed for a 28" x 12" OR 12" x 28" duct opening (measured at the opening), with actual outer dimensions of 30. 5" W x 14. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 27. 75" x 11. 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