Refresh my memory

[cehs]

What factors affect moisture (sweating) inside the flue of an 80% furnace installed in a basement?
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[RIGUY]

below 130degree flue gasses that wont happen at 80% tho check the flue gas

[wogpa67]

short run times = the answer

[DirkRoper]

Not enough heat. Did you downsize the furnace? I've seen moisture run down the flue and fry a circuit board.

[smooth_operator]

Flue gas temp, flue type, flue size, draft.

[Kenoo8]

Are you running the flue into a chimney or other concrete or brick flue?

[cehs]

5" flue, double wall from basement through the middle of the house all the way to the roof (2 story).
Furnace has a 4" going into the 5" along with a 3" from the gas water heater.
I have NOT measured the flue temp.
.

[Kenoo8]

I would measure the flue temp, the furnace is induced draft correct, since the main flue is 5" I am not sure if the standing pilot in the water heater will produce enought heat to keep it from condensating. In a cold climate area I had to insulate the doulble wall flue to stop this problem . Mainly in the basement.