Hi Everyone, I just wanted to take a minute to thank everyone on this site for the great info I was able to gather before doing our install. I would have never thought of putting a block off plate in with our insert, but after reading the posts and responses I am glad I did. We made our BOP out of 20 gauge sheet steel, and used 2" thick Roxul 80 above it cut perfectly to size.The 6" liner was insulated with a 1/2" blanket wrap before dropping it down flue. I stuffed rockwool insulation around the opening of the BOP where our liner comes through. The sides, (where the flanges are), of the BOP were then siliconed using High temp silicone. We had our 1st burn this past weekend and even though it was smaller fires for break in type burns, I was pleased with the results. We have a minor issue with the face plate not lining up correctly that may be due to an inconsistency with the cast on our ash lip plate.... blah blah blah, anyway, I did not have our top face plate on when burning, therefore the insert was open to the inside of the masonry fire box. What I noticed was the large amount of heat that was inside and how hot the BOP got. That right there made the whole project worthwhile for me. knowing that that much heat would be contained within and possibly circulated back to the home rather than up the sides of the flue. In addition, the peace of mind that comes with the fact that if something did go wrong, (Chimney Fire), there would be that added protection to the house. Thanks again, Happy burning.