20"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - Brown [Outer Dimensions 21.75"w x 21.75"h] Color_Anodized Aluminum + Product Details Size –

+ Product Details Size – 36"w X 12"h is the size for the duct opening measurement only

but still very thin

+ Product Details Size – 16"w X 32"h is the size for the duct opening measurement only

Optional Butterfly Damper Available At Asin: B007CNEL1W

20"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - Brown [Outer Dimensions 21.75"w x 21.75"h] Color_Anodized Aluminum + Product Details Size –+ Product Details Size 20"w X 20"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 21. 75" Width X 21. 75" Height Weather and Pest Proof These louvers are especially designed to prevent water from entering your home, and with a built in back 1 2" mesh they also protect you from annoying rodents like mice, rats, birds, and squirrels High Quality Aluminum The premium durable aluminum will never rust and it will never