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  #1  
Old 7/1/09, 4:30 PM
Buck Hartley, CMI's Avatar
Buck Hartley, CMI Buck Hartley, CMI is offline
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Default Condensation on Furnace flue

What do you say about condensation from the furnace, that leaks from the flue.

Thanks!



Mid America Property Inspections, Inc.
Shawnee, KS 66216
www.mapii.com
NACHI # 05110992
KS-Radon Cert.# KS-MS-0035
KS-Termite Cert. # 18933
M0-Termite Cert. # N 5033


Last edited by bhartley; 10/28/13 at 1:29 PM..
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  #2  
Old 7/1/09, 4:42 PM
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Default Re: Condensation on Furnace flue

Buck,

When a flue wall has condensation dripping down (as in your image) it's usually from the flue being too long or it may consist of too many elbows.

What happens is....the exhaust gases are hot when they leave the combustion chamber and vent up through the vent connectors. If the vent piping is too long, the gases tend to cool down at the top portion of the piping (before they actually leave the long pipe) and this cooling down effect will condensate on the inside walls of the piping. This is when the built-up condensation simply drips down from the inner walls of the piping and seeps right out of the seams.

How long is the exhaust piping?
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  #3  
Old 7/1/09, 6:44 PM
Buck Hartley, CMI's Avatar
Buck Hartley, CMI Buck Hartley, CMI is offline
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Default Re: Condensation on Furnace flue

Furnace is located in the basement. Maybe 25 ft. ?

Thanks!



Mid America Property Inspections, Inc.
Shawnee, KS 66216
www.mapii.com
NACHI # 05110992
KS-Radon Cert.# KS-MS-0035
KS-Termite Cert. # 18933
M0-Termite Cert. # N 5033

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  #4  
Old 7/1/09, 7:24 PM
David P. Valley's Avatar
David P. Valley David P. Valley is offline
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Default Re: Condensation on Furnace flue

Quote:
Originally Posted by bhartley View Post
Furnace is located in the basement. Maybe 25 ft. ?

Thanks!
25 feet is quite normal.
I'm willing to bet that the vent connectors have excessive elbows....
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  #5  
Old 7/1/09, 10:17 PM
Buck Hartley, CMI's Avatar
Buck Hartley, CMI Buck Hartley, CMI is offline
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Default Re: Condensation on Furnace flue

Dave,

Thanks! Here is a photo of flue in attic.



Mid America Property Inspections, Inc.
Shawnee, KS 66216
www.mapii.com
NACHI # 05110992
KS-Radon Cert.# KS-MS-0035
KS-Termite Cert. # 18933
M0-Termite Cert. # N 5033


Last edited by bhartley; 10/28/13 at 1:29 PM..
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  #6  
Old 7/2/09, 12:45 AM
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Default Re: Condensation on Furnace flue

Is that step flashing installed behind the sheathing on the rake wall behind the flue? If so, I have never seen that type of installation!
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  #7  
Old 7/2/09, 7:06 AM
David P. Valley's Avatar
David P. Valley David P. Valley is offline
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Default Re: Condensation on Furnace flue

Quote:
Originally Posted by bhartley View Post
Dave,

Thanks! Here is a photo of flue in attic.

Buck,

This flue has a rain cap, right?

It sounds like a stupid question because they come equipped, but ya just never know with today's homeowners.
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