What is the best way to install 12 feet of double insulated stovepipe in a fireplace chimney yourself?

Sorry but your question doesn't really make sense to me. Double insulated stove pipe IS a chimney. If you are LINING an existing masonry chimney these days, you would use a flexible stainless stell liner with an insulation blanket around it (or a special light filler material between the pipe and the chimney) so that condensation and creasote build up does not occur.

If you actually have a straight shot you can purchase lenghts of straight pipe. The damper and lentel(?) shelf need to be removed in most applications. I would highly suggest you have a professional install the liner or at least guide you through the proccess.

If you are wanting to install a double wall stovepipe in a chimney chase (wood framing), then you are looking at another situation. Usually the drywall and exterior siding is not installed until you have set the fireplace and run the pipe. The pipe has to be kept 1 to 2 inches from combustibles.

The clearances can very from different manufacturers. A fire stop is required at each floor level. Once again a professional that knows codes and common practices should perform the installation or guide you through the proccess.

GOOD LUCK, Mike V.

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