This vent cover is designed to mount from the inside behing the vent opening. This vent cover is a solid plate of 19 by 10 inches. It can be mounted flush to the inside wall by drilling screw holes where needed. It mounts in the same fashion as the 145 CFM Double Fans (19x10) or the 220 CFM Triple Fans (19x10).
The solid plate is used to keep air flow blocked from the outside. Often in creating a cross circulation of air, it can be beneficial to block vents to make sure that the air flows all the way across the crawlspace. Additionally, vent openings that are under decks and porches are often a great source of moisture in the crawlspace and it is generally recommended to block those off. These vent covers with solid plates for internal mount allow any existing outside vent covers to remain in place so the look of the exterior will not be affected.