Ok, I know the answer in a perfect world but here goes anyway. With all of the talk in my neighborhood about me lining my flues, one of the neighbors wants to do his too. I went up and took a look at his clay tile masonary chimney and it is the same as mine, 11X7 inside 12x8 outside. The chimney has a paper thin, and I do mean the thickness of a sheet of notebook paper, glaze of hard creosote. I took a pocket knife and chipped off some to the tile to see how thick. If he lines this thing is he really looking at the exploding chimney adventures that Karen Duke talks about? Or if the liner sets this stuff off is he just going to have a seven or eight hundred degree cook-off that probably won't even be noticed? And if he lines it with the crap in there should he hold off insulating the top for this season to give it a place to go if it does light off? If I was in a liability situation like a dealer I would tell him it has to be as clean as a fall morning. I actually believe it ain't gonna hurt anything.