I personally wouldn't install a SS liner yet. You may not ever need to install a liner. As long as the chimney is sound, I would go ahead and use it.
Is your chimney in an interior wall or exterior?
You said it has the original brick lining?? Not a square or rectangular terracotta or clay tube?? As long as the mortor in the brick is sound, it should work fine. If you have concerns about the mortor joints then maybe a liner should be considered.
A coal chimney burning anthracite doesn't need much of a clean out. The chimney will only have a very thin layer of dust that will adhere to the rough brick or flue liner joints. Only the horizontal pipe sections need an ocassional cleaning.
Does the pipe exit your Mark I from the top or rear of the stove?? If from the rear, you can put an elbow or a tee to direct the air up. If you use a tee you can cap the bottom and use it as an ash collector. I doubt that you will get much ash in the collector.
Does your chimney have a cleanout door at base, near the floor?? Most do have a small 6"x6" door. this is all that is needed. Antharcite burns so clean that with a Mark I size stove you probably won't see more than a quart can of ashes all year in the cleanout.
If you do install a liner, There are several connectors made to make the corner. One type is a tee with the leg that comes in from the side attached with a clamp [like a long hose clamp] around the verticle section. the horizontal piece is held in place, with the long hose clamp opened to as large a diameter as possible, the vertical pipe is fed down the chimney through the open loop of hose clamp, then the clamp is tightened.
I'd just cut the hole for the thimble, fit a nice adapter, and put two elbows and a verticle section of pipe in and fire it up.
By the way, galvanized pipe is usually thinner [26 or 28 ga.] and the galvanizing gives off noxious fumes when heated. I'd use heavier black pipe, it usually is 22ga..
I think I covered all the questions. I'm sitting in a hotel room with time on my hands, so ask away with any other questions.
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