Furnace vent flue condensation

Question by Craig

In the last mo I have replaced a 30 y/o furnace w/a 80% furnace. Everything seems to be perfect except I am now getting water puddles at the base of my flue in my basement which I never had before. I have talked to 2 chimney cont.

Both told me the added efficiency in the old flue is creating a condensate problem for my old flue. I am told I need a insert for my flue from top to bottom. Nothing else is vented in flue, electrical water heater. Can I just vent directly from furnace through sill plate like clothes dryer, and what material to use?

1 Answers
Dariusz Rudnicki Staff answered 1 year ago

Hi Craig,
The chimney guys are correct, you need a new, proper size liner for the chimney. It appears that your current flue is oversized, and cooler exhaust gases from the new 80% furnace condensate on the chimney interior walls.
No – you can not vent through the sill plate unless it’s a direct vent type furnace, or 90+ condensing type.

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