Last year I installed a 6'' liner to my fireplace, sealed off the fireplace in two spots, at the shelf and just above the stove with 1'' ridge fiberglass insulation. Removed the shield on my insert and looked at sooty fire brick all winter. Last week I pulled my stove out and cleaned them up a little, they were black big time, also added a damper to the pipe. This stove has been in use for 21 years in this fire place, bought it new in 86, $1400. It was made primarily to burn wood but with a little work it will do coal, I put 4 ton through it last year.