When I moved into my old cabin, it had a small coal stove. It was connected to ordinary 4" galvanized stovepipe (necked down from the 5" outlet on the stove). The stovepipe passed through a wall thimble to the outside where it extended straight out past the eaves, then an elbow and it went up a bit past the roof. At one point I replaced the pipe because it was rusted out (to be expected when you're burning coal). The inside of the thimble had some kind of insulating material, I'm guessing asbestos. It actually worked quite well, drafted OK, but my question (strictly curiosity as this installation is now history) is, was this once considered an OK installation? Were asbestos wall thimbles the way it was done? I know ventilated wall thimbles are used for interior walls nowadays. The stove and cabin were both 1920s vintage, but I don't know when the stove was installed in the cabin... it was likely a later installation of a used stove, and considering the way these places tended to get remodeled (amateur renovations with no thoughts of code) , somebody may have stuck the stove into the pipe left over from a hot water heater installation. Not to worry, when I moved to a new cabin, I took the stove with me as the buyer didn't want it, and did a proper install with 6" insulated chimney.