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Old 12-03-2011, 10:41 AM   #1
Cobra64
 
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Lining 6" metal flue with 4" Class B vent


I have an 80% gas furnace with a 4" exhaust attached to a 40 year old 6" double wall gas flue approximately 15 feet straight from basement to cap. It runs in a chase up the center of the house. A 4 " pipe runs approx. 5 feet from the furnace to the bottom of the flue. I have condensation running down the flue interior and from the reducer joint. The flue is clear. I could seal the joint, but then the water just ends up in the heat exchanger I would assume.
I am guessing the velocity of the gasses slows enough entering the 6" pipe to allow the condensation to form + interior surface area is too large to get warm enough to prevent it.
Can I ("within code") slide a 4" class b pipe inside the existing pipe? It will fit, just don't know if it is legal AND should that resolve the issue? OR is the only solution a condensation drain?
Thank you!!

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Old 12-03-2011, 12:39 PM   #2
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Lining 6" metal flue with 4" Class B vent


It is legal. Our Pro chimney company slides smaller liners into 6 inch single wall liners all the time. Should have 4 inch B vent from the furnace to the chimney also. Loses a LOT of its heat on the way to the chimney. without it the moisture will run back into your furnace and SERIOUSLY damage it.

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Old 12-04-2011, 01:14 AM   #3
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Lining 6" metal flue with 4" Class B vent


Using the old chimney as a chase is perfectly allright unless your hot water heater uses that old chimney.
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Old 12-04-2011, 08:16 AM   #4
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Lining 6" metal flue with 4" Class B vent


depending on the combined BTUs of furnace and H2o heater 4" may be big enough to do both and be OK
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Old 12-05-2011, 09:15 PM   #5
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Lining 6" metal flue with 4" Class B vent


Appreciate the input very much. Looks like a project for a weekend.

Cobra
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