Recently had a level 2 inspection and cleaning done on fireplace flue and furnace flue and the inspector recommends that both be relined due to deterioration of the clay tile. House was built in 1926. Oil boiler, 99,000 BTU. I had two contractors out to give a second opinion and estimate on relining the furnace flue (FP will have to wait).
Contractor 1 will break out existing 8x8 terra cotta tiles and reline with an 8" stainless liner, insulate with light masonry fill and cap.
Contractor 2 says breaking up the existing tiles can damage the masonry and the vibrations could crack the plaster inside the house. He says to leave the existing terra cotta tiles and go with a 6" liner that will fit in the available space, then install a reducer to tie the 8" exhaust from the boiler into the 6" liner.
Contractor 1 says 8" is needed to maintain a proper draft and that not removing the old terra cotta means you either aren't willing or don't have the equipment to do the job right. Contractor 2 showed me a sizing chart that says 6" will handle almost 200,000 BTU for the 24' run that I need.
So, are these both legitimate approaches to doing this job or is one or both of these guys full of it? My main concern is I don't want to wake up dead because someone screwed this up. Thanks for any input.