My wife and I just bought an older farm house (circa 1901) and we've
been enjoying nightly fires. About a week ago we noticed smoke
starting to accumulate in the living room and got nervous. I had
installed a roof top damper weeks earlier, but we had many fires
without incident after I installed it.

With the lights off and using a flashlight, I realized smoke was
belching out from behind the mantel and along the brick trim all the
way down to floor level. I realize this is a potentially deadly
problem. My theory is that smoke is escaping through the old mortar
joints in the flue tiles, leaking down around the flue inside the
brick chimney above the firebox, and ultimately into the house (and
who knows where else).

Given that we definitely want to enjoy the open fireplace (we just
bought 7 cord of mixed hardwood!), is relining the chimney with a
flexible liner an option? I have read some warnings about the danger
of using a round liner and the resulting impact on flue diameter
reduction. We are on a tight budget, but the fireplace is one of the
few luxuries we allow ourselves! The existing flue is in the
neighborhood of 12" x 12" and is not a straight shot (one bend).
Looking down the chimney from the top I can see a number of misaligned
tiles. I have researched "squarized" liners (their grammar...not
mine) and the cost is steep.

Is there any economical way for me to attack this problem? I have a
fair amount of construction experience, but I don't know one wit about
flue sizing, etc. My concerns are that I will put in a flue, only to
find that (a) it's undersized, or (b) smoke is escaping the smoke
chamber below the flue itself and I'm no further ahead.

We have guests arriving in three weeks and I would really like to have
this taken care of so we can enjoy our new home with family.

Any advice would be greatly appreciated.

Thank you,
Greg