20"W X 20"H [Duct Opening] 4-Way Aluminum Curved Blade Adjustable Air Supply HVAC Diffuser [Outer Dimensions: 21.75"W X 21.75"H] Material_Steel + Product Details Size -

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

ensuring your space stays dry and secure

Actual Filter Size – 29 3/4"w x 35 3/4" x 1"

ensuring it fits most standard thermostat models

+ Product Description Introducing the 6" Butterfly Damper – Your Solution for Controlled Airflow

20"W X 20"H [Duct Opening] 4-Way Aluminum Curved Blade Adjustable Air Supply HVAC Diffuser [Outer Dimensions: 21.75"W X 21.75"H] Material_Steel + Product Details Size -+ Product Details Size 20"w X 20"h is the size for the duct opening measurement only, actual front end outer dimensions are 21. 75" width X 21. 75" height. Design Individually adjusting curved blades for better air flow control. Screws Included High Quality Aluminum The premium durable aluminum will never rust and it will never wear through leaving the material with an elegant, beautiful, and smooth surface, adds a luxurious touch to any home.