28" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Aluminum - Cube Core + Product Details Size –

+ Product Details Size – 24"w X 28"h is the size for the duct opening measurement only

+ Product Details Size – 25"w X 18"h is the size for the duct opening measurement only

+ Product Description Secure your thermostat with the heavy-duty Beige Metal Thermostat Guard

+ Product Details Perfect Fit & Easy Sizing - Designed for a 8" x 34" or 34" x 8" duct opening (measured at the opening)

+ Product Details Perfect Fit & Easy Sizing - Designed for a 18" x 12" OR 12" X 18" duct opening (measured at the opening)

28" x 18" Cube Core Eggcrate Return Air Filter Grille for 1" Filter Aluminum - Cube Core + Product Details Size –+ Product Details Perfect Fit & Easy Sizing Designed for a 28" x 18" OR 18" x 28" duct opening (measured at the opening), with actual outer dimensions of 30. 5" W x 20. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 27. 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