Abstract: A trim assembly comprising an integral trim member having a generally L-shaped cross-section, in which one leg of the L is adapted for attachment to a wall to serve as the casement, while the other leg (flange section) projecting towards the window is adapted for attachment to the jamb surface of the window opening. The interior surface of the flange section is provided with closely-spaced, longitudinal grooves extending the length of the trim member. These grooves, preferably spaced at a distance of about 1/8 to 1/2 inch, are easily cut or broken off whereby the width can readily be modified to properly fit a wide variety of jamb-widths. The instant trim member, featuring a flange projecting towards the window, permits for the design of a hollow enclosure which can serve as a housing for a small blower to provide a source of flowing, preferably heated, air.