Long Winded Post
My place has a "manufactured" fireplace from the ?70's or 80's ? which had a wood stove insert in it. I fired the heck out of this thing for years. Retired it in 2007 and gave the stove away when I installed the owb. This outfit has the low clearance 8" i.d. flu which is ? triple? wall, which runs thru the attic into a metal chimney that's supposed to look like red brick,,and does, kind of look like a masonry chimney.
Anywho, for experimental purposes I ran 16' of 6' black stove pipe down this thing. Using a black "pie plate" trim ring at the top and bottom of the 6" black pipe to keep it centered in the 8" pipe..follow me? Yeah, right!
Then I hooked up a small wood stove which sat inside the "fireplace" and fired it with a small fire. I began checking the whole flu set up from inside the attic to out on the roof. I fired the stove to wide open and ran the heck out of it for a couple/few hours, all the while checking things out from the stove, into the attic and out on the roof. The flu/black pipe was reading 475-500 degrees just above the stove. The outside of the original flu, inside the attic never got hot.
I could lay my hand on it and it was "warm".
I only did this as an experiment, in the event of a prolonged power failure, to see if it would work. I had fire extinguishers, big ones, in the house, attic and on the roof. I would not count on this for a prolonged heat source. I took the little wood stove and 6" pipe out of the fireplace/flu and it's no longer used for anything but stashing the kids toy box. If I should ever go back to an indoor wood stove, I will completely demo this old "fireplace" and install the appropriate s.s. flu, for insurance/peace of mind.
Spend yer doe on a new s.s. liner as has been suggested, install it to code, your insurance guy will be happy and you should sleep better at nite, and your stove will/should run better. peace!