A louver assembly and a method for installing the louver assembly into an opening in a wall of a structure are provided wherein the louver includes a frame which and a separate louver section which may be mounted within the frame after the frame has been mounted in the opening in the wall. The frame defines a central channel which extends from an interior opening to an exterior opening. The frame includes a frame flange extending from an exterior edge of the central channel so that, when the frame is in a desired position within the hole in the wall, the frame flange extends around the entire perimeter of the hole to seal the perimeter of the hole. The louver section is selectively mountable within the central channel so that it is prevented from passing through the exterior opening. When the louver section is in a desired position within the central channel, the frame is sealed so that air is prevented from passing between the frame and an outer surface of the louver section.