16"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 17.75"w x 21.75"h] 6" Diameter 75" width X 21

75" width X 21

+ Product Details Size - 4"w X 36"h is the size for the duct opening measurement only

But they are also the most visible representation of you air system

+ Product Details Size – 6" x 6" is the size for the duct opening measurement only

16"w X 20"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 17.75"w x 21.75"h] 6" Diameter 75" width X 21+ Product Details Size 16"w X 20"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 17. 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