sounds like a metal chimney has served you well, Oliver. The one i picked up has a nice coating of creosote in it, so maybe it will take a few years for the flyash to even get to the metal
this garage/ coal boiler project has exceeded my intended budget so far (my wife makes it a point to remind me often) ... it is metal for me for now. I have a long way ( and a lot of parts) to go ... thanks everyone.
Let me tell you what happens when you don't take care of a metal chimney. I bought a used metal-bestos chimney at an auction. It was going to be temporary for the shop, as I knew I was going to install a masonry chimney down the road. Because of the slippery metal roof on the shop, I never cleaned the chimney. Like I said, it was temporary. Last year, when inspected from below, I noticed the inner lining was eaten away enough that one side leaned across, touching the opposite side. I used it that way last winter. It kind of acted like a manual damper. I took down the metal chimney this fall. All that remained was the dense filler material. The inner stainless pipe was GONE. How is that for getting use out of a metal chimney???