16" x 36" or 36" x 16" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 10" Diameter actual front end outer dimensions

actual front end outer dimensions are approximately 38 5/8" width X 34 5/8" height

For 14" Round Duct Opening - Spiral or Flex

actual front end outer dimensions are 22" width X 6" height

positioning supply and return grills accordingly

+ Product Details Size - 26"w X 18"h is the size for the duct opening measurement only

16" x 36" or 36" x 16" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 10" Diameter actual front end outer dimensions+ Product Details Perfect Fit & Easy Sizing Designed for a 16" x 36" OR 36" X 16" duct opening (measured at the opening), with actual outer dimensions of 18. 5" W x 38. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 15. 75" x 35. 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