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Bob F

wrote:
Going through the quote process for my new furnace and AC and came up
with two questions:

2 - The new furnace will be direct vent, so it leaves the gas water
heater orphaned on the existing chimney that was shared with the gas
furnace. Is a chimney liner required or recommended? Chimney is
clay flue lined, most of chimney is entirely within the house, except
the last 5 ft or so which is in a wood siding chase above the roof
line. Don't have the exact measurements of the flue without going on
the roof, but guessing it's about 9 X 6 or so. Again, one company
says must do, the other says not needed.

My understanding is that a chimney built for a furnace will be too big for just
a water heater. Moisture will condense out onto the liner and, over time, break
it down. I installed a b-vent when I did this.