Choose between the small and large black faceplate to close the gap between the insert and the fireplace so you do not have to see inside the actual fireplace. The faceplate is used when there is a smaller gap between the insert and the fireplace. The small faceplate will cover a fireplace opening less than 35 7/8" Wide x 24 3/8" Tall and the large faceplate will cover a fireplace opening size less than 40 7/8" Wide x 26 7/8" Tall.