I recently went through the process of having my 2 flue chimney rebuilt from
the roofline up. I then lined one of the flues with a SS liner for a
woodburning fireplace insert.
The 2nd flue is currently being used by my gas furnace and HWH. I noticed in
the attic that some of the mortar is crumbing on that flue. (This is the
original part of the chimney, not the new part, which is just from the roof
up.) I plan to repoint these sections this spring. After reading some
articles online & in magazines, I think the problem is that my boiler is
causing too much condensation in the cold part of the chimney (in the
attic). This is causing the deterioration of the mortar.
This said, I am thinking of either a) purchasing a power vent and
redirecting the gas exhaust out the side of the house OR b) lining the 2nd
flue with a gas-compatible liner.
The cost seems about comparable ($1000-$1500 if I do it myself).
Any pros/cons to consider?