Condensation on outside of exhaust vent


  #1  
Old 01-23-10, 08:52 AM
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Condensation on outside of exhaust vent

Hi

I have a Lennox pulse furnace that has a exhaust PVC pipe running up through the walls (interior wall) to the roof. Recently noticed some mould near the baseboard and today after taking off some drywall found the exhaust vent surrounded by soaking wet fibreglass insulation. There is no exhaust leak as far as i can tell and this is on the main level (furnace in basement) and there is one more floor before the exhaust enters the attic. I removed as much of the wet insulation as i could but will have to remove the whole wall to get the rest of it.

Any ideas where this might be coming from or is this simply a question of hot exhaust air meeting cooler room air in the wall?
Thanks

Samer
 

Last edited by samer; 01-23-10 at 11:43 AM. Reason: Sentence
  #2  
Old 01-23-10, 01:26 PM
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Condensation

I seriously doubt it is condensation. Either you have an exhaust leak or rain water is coming down the outside of the pipe (most likely).
 
  #3  
Old 01-23-10, 03:41 PM
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Hot exhaust air meeting cool air or surface will cause condensation, but I would expect that to be contained inside the vent pipe. If exhaust gas is getting inside your wall, that is alother problem. If it is water leaking from above you may see it now that the wall is open.

Can you see this pipe from the attic, check the insulation up there.

Now, I'm thinking as I write, is the hole where the vent pipe comes up through the wall open to the basement. Possibility is warm basement air being drawn into that cold space and there is your condensation. So maybe not hot exhaust, but just moist inside air, which is very common. If so, use some fire rated can foam and seal at will. While you are at it, all penetrations into the basement and attic suffer the same potential. In a way you are lucky you noticed the issue as most go undetected and slowly cause rot or mold.

Let us know what you find. Added a link on air sealing:
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
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Old 01-23-10, 04:22 PM
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Thanks for the replies so far.

Taking another look at the exhaust pipe, i figured out that there is a bend in the pipe in the ceiling as there is no wall above the wall that i opened. So i opened the wall up close to the ceiling and again found soaked insulation and studs with some mould .

The problem seems to be coming from the area of the bend which i cannot see from the main level. So the next step will be either to take down the ceiling (loud protests from the woman who runs my life) or remove the subfloor from the area above (hardwood) (similar loud protests!!).

Since the ceiling itself appears dry and no signs of water, i think it may be the lower end of the elbow joint which is leaking and the water running down the pipe. The problem is that there is no way to see or feel the elbow without one of the options mentioned above.

Will update later as to next step.

PS Is this a significant carbon monoxide risk right now? I might have to turn the furnace off until i figure out the next step and its a bit cold right now here in canada!!
 

Last edited by samer; 01-23-10 at 04:23 PM. Reason: spell
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Old 01-23-10, 05:17 PM
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I take is either inside the wall the installer did not seal the PVC pipe or maybe the insulation is not that great and the HOT vent and cool air..BAM water.

In my last house I got this on the bath fan...Water all over and drove me nuts. I insulated the bath fan hose 3" and no more water.
 
  #6  
Old 01-23-10, 05:26 PM
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I would not anticipate a CO problem as it is still venting and the hole would be very small. Condensate does form inside the pipe, that is one of the side effects of a high efficiency furnace. The water is usually drained off in the basement to a sump.

Sheetrock is a lot easier to repair as opposed to hardwood. Does she need a new dish washer, or car?

Bud
 
  #7  
Old 01-24-10, 04:06 AM
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Run the pipes horizontal to side wall. completely eliminate the problem
 
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Old 01-24-10, 09:52 AM
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Hi
Well i took off part of the ceiling and now can see the elbow joint. The leak is from the bottom part of the elbow, about a drop per 2 minute and runs down the pipe.

So the next question is should i replace the elbow with some coupling and pipe or call the company that put in the furnace in the first place (the house is about 16 years old) and ask them to fix it.

If i do it myself there might be some other problems. The current pipe is grey and labelled as Lennox Pulse Vent 2" Scepter PVC 1120. The gas vent pipe available at my HD is a white pipe (i think type 636). Are the two compatible and what cement would i use for these two pipes?

As for the side running idea; i don't know why it was not done when the house was built. Now it may be very difficult as the furnce is in the middle of the house with rooms on all sides. Would probably have been simpler than this run with its bends and risk of a nail going into it by hanging a painting etc.

Samer
 
  #9  
Old 01-24-10, 10:00 AM
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Worth a call IMO. Worst they are going to say is a big number. They might actually feel responsible, even after 16 years, good dealers are like that.

Bud
 
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Old 01-26-10, 09:07 AM
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Update 2

Well i called in the previous company, someone came in and cut out the elbow joint and replaced with black ABS pipe elbow cemented at the elbow but used rubber couplings with steel bands to tie the old and new together. I was a bit surprised that they used regular ABS and rubber but the tech said that this was acceptable and gave a bill for $175.


So the leak is hopefully gone, next step is drywall this weekend.

Samer
 
  #11  
Old 01-26-10, 09:14 AM
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Well, I guess now you at least don't have to worry about something going wrong and you being responsible. In today's times, that is probably worth the 175. D@rn, (while kicking backside) I have to increase my prices.

Bud
 
 

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