8"w X 36"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 9.75"w x 37.75"h] ceiling + Product Details Perfect Fit

+ Product Details Perfect Fit & Easy Sizing - Designed for a 30" x 20" OR 20" x 30" duct opening (measured at the opening)

including the ability to mount without removing the thermostat when using the ring base

+ Product Details Size – 20"w X 40"h is the size for the duct opening measurement only

Actual Filter Size – 25 3/4"w x 33 3/4" x 1"

+ Product Details Size – 24" x 30" or 30" x 24" is the size for the duct opening measurement only

8"w X 36"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 9.75"w x 37.75"h] ceiling + Product Details Perfect Fit+ Product Details Size 8"w X 36"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 9. 75" Width X 37. 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 wear