28"w X 18"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 29.75"w x 19.75"h] Supply Grille The 1/2" black insulation

The 1/2" black insulation

and waste gases transmission lines

actual front end outer dimensions are approximately 18 5/8" width X 14 5/8" height -

and the second number represents the height

+ Product Details Size – 30"w X 28"h is the size for the duct opening measurement only

28"w X 18"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 29.75"w x 19.75"h] Supply Grille The 1/2" black insulation+ Product Details Size 28"w X 18"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 29. 75" Width X 19. 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