36" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 8in diameter Ideal for Walls & Ceilings:

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

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actual front end outer dimensions are approximately 12 5/8" width X 28 5/8" height

+ Product Details Universal Fit - Accommodates almost any thermostat with dimensions of 8-1/4" H x 5-3/8" W x 3-1/2" D

Ideal for Walls & Ceilings: Designed for seamless installation in standard 10” x 8” duct openings

36" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 8in diameter Ideal for Walls & Ceilings:+ Product Details Perfect Fit & Easy Sizing Designed for a 36" x 18" OR 18" x 36" duct opening (measured at the opening), with actual outer dimensions of 38. 5" W x 20. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 35. 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