We will be building a new home this spring and will have a high efficiency wood burning sealed unit fireplace with a blower. On the blueprints the back of the fireplace on the outside wall sticks out in a box a couple of feet, I'm assuming that is where the pipe goes to the roof. Does that box need anything else inside of it or will it just be framing and the pipe with siding on the outside wall? My friend was wondering if we would put some fireproof drywall inside that box or insulation? I am under the assumption that it's just the pipe, framing and siding. Am I correct or am I greatly missing something important?