Well, you do make some points, but I think clay is not that porous when in good condition. I don't know how long a stainless liner will last but I would expect clay liners to last a good 50 years. Replacing clay liners in an existing chimney though, is an expensive proposition....probably ten times as expensive as the stainless expandible sleeve.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.