I have a regency medium insert that I have been using for about 6 years now. It currently does not have a block off plate above it right now but am going to install one but would like to ask some questions first. First off is 26 gauge steel ok and how much rock wool insulation should I stuff in the damper area. My chimney is in the middle of the house so its an interior chimney. Also how much of a difference will me doing this make as far as the amount of heat I will get after I do this. In your opinion is it really worth doing this on an interior chimney. I can tell you I do feel the walls get warm above the insert on the second floor. So I must be loosing some heat but is this really worth the work and material. Also does anyone have any rock wool they dont need. I am in North Jersey. Thanks All.