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QUESTION:My mom is having her forced air gas furnace replaced. The current
furnace (~17 yrs old)vents through a masonry chimney. The guy
installing the furnace says that because the furnace is more energy
efficient (~80%), the temperature of the flue gases is considerably
lower - causing the moisture in the flue gases to condensate inside the
chimney. He says that the moisture is acidic and will damage the
chimney liner. The proposed solution to the problem is a $400 stainless
steel liner.
Does this make sense to anyone else? The old furnace was probably
65-70% efficient, I doubt that the exhaust gases are that much cooler in
the 80% furnace. The house was built in the 1950's and has always used
gas heat - there does not seem to be any damage to the chimney so far...
ANSWER: I can only comment on some very recent experience. I just bought my first
gas, forced hot air heated house. It has a new high efficiency furnace
that vents directly out through a pvc drain pipe. The condensation goes to
a pump near the base of the unit that then goes to a water drain. The
thing that I had to address the first weekend was a messed up pump. I was
correctly warned that the water is acidic so I used gloves when I took the
pump apart and cleaned it. The house also has a "wood-style" gas stove and
when I had the chimney inspected I asked about the condensation. The
chimney for that is not lined but that unit burns hotter than many
furnaces.
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