Ice/Condensation Around Aluminum Chimney HVAC Exhaust
Ice/Condensation Around Aluminum Chimney HVAC Exhaust
(OP)
Here is the situation, moved into this house about 1 year ago in the winter. About 6 months later we replaced the roof, the roofer also replaced the aluminum chimney that wraps the exhaust vent for a high-efficiency gas furnace. The duct/vent is 8" and it runs thru an unheater attic area before exiting the roof via the false chimney wrap. The duct work is insulated in the attic, except for the last few feet beyond the roof line.
Prior to having the roof replaced I never saw any ice form around the chimney like we have now. When the furnace is running you can watch the water drip down from the top of the chimney, some of it drips back into attic.
Thoughts on what is causing this? Please see the attached pic.
Thanks
Prior to having the roof replaced I never saw any ice form around the chimney like we have now. When the furnace is running you can watch the water drip down from the top of the chimney, some of it drips back into attic.
Thoughts on what is causing this? Please see the attached pic.
Thanks





RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
Thanks!
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
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RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
Covering it with some spare shingles might be enough. You might also want to overhang the edges, to delay mixing with cooler ambient air until the smoke leaves the chimney.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
I would suspect standard if the vent is 8-inch metal.
The cap that you have has too much surface area. You might be able to raise it - allowing flue gas to more fully mix with ambient air before it hits the cold cap surface.
Otherwise, you should get a more appropriate cap designed for an 8" gas vent.
If your furnace is a standard one you need to address this quickly. The condensed products of gas combustion are acidic.
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
The fact that its an 8" vent might just be the byproduct of an earlier heating system, since the house was built in the 50's...
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
Go find the manufacturer's web site and look at their recommended vent materials, diameter and termination.
Do you have a gas-fired water heater feeding the same stack?
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
From reading the manual, it seems like the exhaust vent should be 4" not 8", but its pretty technical about all of the different ventilation configurations...
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust
That's not a condensing furnace. It's not even a high-efficiency furnace. In fact, it's a pretty crappy efficiency furnace.
If you have central cooling the PVC drains are probably condensate.
Just get a standard cap for a 8" diameter flue and you should be fine.
RE: Ice/Condensation Around Aluminum Chimney HVAC Exhaust