In article ,
Bob F wrote:

"Brian V" wrote in message news:PoGdnfg-

The flue gases don't touch the brick. There's a clay type liner in there
then surrounded by brick. The brick is structural only.

My chimney has no liner. Are you sure?

Bob



He probably is sure, but he is not correct. Flue liners are required
by many current building codes but go back a few decades or so and
this was not the case. Older houses often had brick chimneys with no
liner, and deterioration was/is a problem. High efficiency furnaces,
which have lower flue temperatures, do tend to make it worse because
of condensation, as some other psoters mentioned. The condensation is
worse than plain water for masonry, because it is slightly acidic,
which is generally harmful to mortar, and possibly the bricks
themselves.
--
No dumb questions, just dumb answers.
Larry Wasserman - Baltimore, Maryland -