28" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Adjustable Return + Product Details Size -

+ Product Details Size - 12"w X 28"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 18" x 28" OR 28" x 18" duct opening (measured at the opening)

+ Product Details Size - 24"w X 34"h is the size for the duct opening measurement only

Operating temperature from -40°f to +248°f [-40°c to +120°c]

They seamlessly integrate into sheet rock plaster frame ceilings as well

28" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Adjustable Return + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 28" x 20" OR 20" x 28" duct opening (measured at the opening), with actual outer dimensions of 30. 5" W x 22. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 27. 75" x 19. 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