18" x 36" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 12in diameter at predicted low air motion

at predicted low air motion 35 fpm in the zone of occupancy

actual front end outer dimensions are approximately 26 5/8" width X 30 5/8" height

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

actual front end outer dimensions are approximately 18 5/8" width X 20 5/8" height

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

18" x 36" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 12in diameter at predicted low air motion+ Product Details Perfect Fit & Easy Sizing Designed for a 18" x 36" OR 36" x 18" duct opening (measured at the opening), with actual outer dimensions of 20. 5" W x 38. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 17. 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