20"w X 30"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 21.75"w x 31.75"h] Aluminum - Cube Core actual front end outer dimensions

actual front end outer dimensions are approximately 36 5/8" width X 34 5/8" height

+ Product Details Size - 18"w X 24"h is the size for the duct opening measurement only

Actual Filter Size – 11 3/4"w x 27 3/4" x 1"

Optional Butterfly Damper Available At Asin: B007CNEL1W

+ Product Details Size – 30"w X 32"h is the size for the duct opening measurement only

20"w X 30"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 21.75"w x 31.75"h] Aluminum - Cube Core actual front end outer dimensions+ Product Details Size 20"w X 30"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 21. 75" Width X 31. 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