The insert is 28" wide x 32" tall x 12" deep. The viewable area is 28" x 22"; the top 10" holds the projection hardware and is meant to be framed or trimmed over. If your opening is wider or taller, frame around the insert with wood, stone or tile so it looks built in. If your opening is too short, check the height behind the front lip: most fireplaces get taller inside, so the insert can often sit a few inches back, like logs in a real fireplace. Do not build anything custom until you have the insert in hand.