# Why is water leaking from the furnace pipe in my attic?



## watai0102

I have a gas furnace that is approx 10 years old. There is a 5 inch galvanized furnace vent pipe in the attic that goes out the roof. Water is leaking from the seams of this pipe when the furnace runs. Roof has been checked and sealed, it isn't the issue. Is this condensation, what can be done to fix it?


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## cda

When the heater runs

Or the air conditioner runs??


What does your a/c heater company say?

And I guess it happens rain, sun or snow??

Any certain time of the year?


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## steveray

Probably condensation....properly size the flue and seal the joints....


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## classicT

Most likely you have the furnace running (heating), which in turn releases some heat via the vent. The warm vent which is in contact with cool and humid Fall air is producing condensate. The condensate then runs down the vent stack and pools at the joints, thus appearing to be the joints leaking.

If you are worried, Fall is a good time to have you unit serviced - have a local HVAC company come do a preventative maintenance inspection.


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## mtlogcabin

Propane undergoes combustion reactions in a similar fashion to other alkanes. In the presence of excess oxygen, propane burns to form water and carbon dioxide.

If it is a propane furnace your problem may be with in the unit itself. Have it serviced since it could be a dirty orifice or other issues.


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## conarb

The new high efficiency furnaces expel all kinds of water, but the vents are usually PVC and they have a separate ½" PVC condensate drain that has to go somewhere, the the OP says he has a galvanized vent, there is a possibility that a conventional furnace was replaced with a high efficiency furnace and the galvanized vent wasn't changed.


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## classicT

mtlogcabin said:


> Propane undergoes combustion reactions in a similar fashion to other alkanes. In the presence of excess oxygen, propane burns to form water and carbon dioxide.
> 
> If it is a propane furnace your problem may be with in the unit itself. Have it serviced since it could be a dirty orifice or other issues.



All combustion produces water


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## tmurray

conarb said:


> The new high efficiency furnaces expel all kinds of water, but the vents are usually PVC and they have a separate ½" PVC condensate drain that has to go somewhere, the the OP says he has a galvanized vent, there is a possibility that a conventional furnace was replaced with a high efficiency furnace and the galvanized vent wasn't changed.



If this is the case, the duct should be properly sized for the newer equipment. Old equipment lost a lot of heat through the flue, which allowed for the use of larger flues, when replacing with more efficient units, the draw up the flue may not be enough to pull all the combustion gases out, causing them to remain in the flue. Once it cools down the water condenses. This could be a life safety hazard as the gases could be drawn back into the home if the flue or furnace is not sealed properly


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## classicT

conarb said:


> The new high efficiency furnaces...



10yo furnace, see the initial post


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## cda

Where is Wata our early morning poster


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## conarb

Ty J. said:


> 10yo furnace, see the initial post


I remember getting high efficiency furnaces 15 years  ago, so the are older than that.


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## Paul Sweet

Is it a single-wall pipe or a B-vent (double wall)?  Is the furnace atmospheric combustion, induced-draft, or condensing?

I remember specifying pulse furnaces in the late 70s, and induced-draft furnaces in the 80s.


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## Gregg Harris

CFM on furnace could also be too high causing flue temperature to be to low and condensing before exiting flue, same scenario as over sized flue or burners under fired. Set with combustion analyzer to eliminate


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## Heath hosick

watai0102 said:


> I have a gas furnace that is approx 10 years old. There is a 5 inch galvanized furnace vent pipe in the attic that goes out the roof. Water is leaking from the seams of this pipe when the furnace runs. Roof has been checked and sealed, it isn't the issue. Is this condensation, what can be done to fix it?


I have a 5 years hvac unit and it starting to leak at the PVC (the elbow joint)going out to the roof. The roof is 2 years old. So I'm wandering if its condensation as well


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## John Callaghan

According to me, your leak could be a result of the condensation tubing becoming blocked or from breaks in the line. It could also be a result of the floor drainage becoming outflow.


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