I am thinking that I will res-ize the thimble back down to 6" in the spring. I'd hate to spend the loot on a 6" baro and more stove pipe but I just checked and the ash it is building up again at the elbow where it exits the stove. What about going 6" up from furnace to an increaser to the 8" thimble? I wonder if the draft would be enough to carry the fly ash through the 8" thimble for a distance of about 10-12" (foundation wall) and then drop into the chimney clean-out. Then at least I would not have to re-size the thimble back down to 6".