Installed the insert about 1.5 months ago. Figured I would do the first sweep today and see what came out. About 2 cups of fluffy brown soot. I took it out to the back yard and tried to light it off with a torch. Held the torch there for a few minutes and there was nothing that would burn so I'm guessing thats good. The part that I wonder about is the underside of the chimney cap. Does anyone worry about scrubing those clean? That was the only area where there was some glazing and looked like true cresote. The 6" liner is insulated and is 18' high.