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  1. #1
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    Default excessive moisture on duct system.

    I looked at a 5yr old house for my neighbor yesterday. The crawlspace is well ventilated with a vaporbarrier covering 85-90% of the ground. The issue is that the duct system insulated wrap is competely saturated and condensating thru the wrap and dripping on to the vapor. The system appears to be neatly installed with no evidence of cut insulation or loose tape. I cut several 1/2" slits in the wrap, in which water trickled out a steady rate. It appears that the insulation is completely saturated thru out the entire duct system. Any ideas on what could be causing the entire duct system to do this and any advise on a corrective action? I have told the HO to contact the installer and get them to look at it. But the house being 5 years old, i dont know if the installer can be held liable or not.

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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    I looked at a 5yr old house for my neighbor yesterday. The crawlspace is well ventilated with a vaporbarrier covering 85-90% of the ground. The issue is that the duct system insulated wrap is competely saturated and condensating thru the wrap and dripping on to the vapor. The system appears to be neatly installed with no evidence of cut insulation or loose tape. I cut several 1/2" slits in the wrap, in which water trickled out a steady rate. It appears that the insulation is completely saturated thru out the entire duct system. Any ideas on what could be causing the entire duct system to do this and any advise on a corrective action? I have told the HO to contact the installer and get them to look at it. But the house being 5 years old, i dont know if the installer can be held liable or not.
    It is being caused by the cold duct work and the warmer air in the crawlspace.
    It is very common in many areas and I think it has been worse this year in my area of middle TN with all of the excessive heat and humidity we have had.

    It does not take long for the moisture to occur and saturate the insulation. Once it becomes wet, it takes forever to dry.

    Is the crawlspace "sucking" air in or does it have positive air pressure? If it is sucking then this is a big part of the problem; warm humid air is being drawn into the crawlspace and it is meeting the cool air ducts.

    Scott Patterson, ACI
    Spring Hill, TN
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    Default Re: excessive moisture on duct system.

    Water is caused by condensation. Air leaking onto ducts/under insulation of the ducts wil cause this. . . I recommend the crawlspace vents be closed. A continuous vapor barrier cover installed over the entire floor (dirt), and outside walls be insulated. Cold damp or warm moist air should be kept outside. The crawlspace is treated as conditioned space. Other wise all air ducts (air sealed), water supply pipes and underside of the crawlspace ceiling should be insulated.
    By the way all crawlspaces suck!

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  4. #4
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    Default Re: excessive moisture on duct system.

    at this point, does the HO, remove the duct wrap and have the system inspected and repaired? Or is this a natural occurance and really nothing to worry about?


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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    at this point, does the HO, remove the duct wrap and have the system inspected and repaired? Or is this a natural occurance and really nothing to worry about?
    Yes IMO I'd replace the duct wrap and provide a better vapor barrier on the insulation jacket. Wet insulation is a bad thing . . .but first . . .

    Be very sure that there is not a leak from another source. A leaky pipe from a shower or even drain perhaps?


  6. #6
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    Default Re: excessive moisture on duct system.

    . . .but first . . .

    Be very sure that there is not a leak from another source. A leaky pipe from a shower or even drain perhaps?[/quote]

    no plumbing leak that i can see, just every inch of duct has condensation on the bottom of it. All of it.

    Today 02:41 PMJames RisleyQuote:

    Originally Posted by Scott Lee
    I looked at a 5yr old house for my neighbor yesterday. The crawlspace is well ventilated with a vaporbarrier covering 85-90% of the ground. The issue is that the duct system insulated wrap is competely saturated and condensating thru the wrap and dripping on to the vapor. The system appears to be neatly installed with no evidence of cut insulation or loose tape. I cut several 1/2" slits in the wrap, in which water trickled out a steady rate. It appears that the insulation is completely saturated thru out the entire duct system. Any ideas on what could be causing the entire duct system to do this and any advise on a corrective action? I have told the HO to contact the installer and get them to look at it. But the house being 5 years old, i dont know if the installer can be held liable or not.


    What is the condition of the vapor barrier covering the duct insulation wrap? How did they handle the places where the duct insulation ended? Is the duct insulation covered with tape or covered with vapor barrier at those ends? Are the register boxes completly covered with vapor barrier?

    James this is probably just my ignorance. I assumed (yes i know) that the foil backer on the insulation was the vapor barrier for the duct. It appears to be in great shape, taped really well and does cover the bottom of the register boots. I didnt look closely at the boots but i think they are insulated also.

    Im not an HVAC guy at all, i just didnt know if this was a common occurance in the deep south (south GA). i know its humid, but i would think that the duct system shouldn't sweat this bad.


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    Default Re: excessive moisture on duct system.

    Were all the duct connections sealed with some type of mastic?

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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    .
    Im not an HVAC guy at all, i just didnt know if this was a common occurance in the deep south (south GA). i know its humid, but i would think that the duct system shouldn't sweat this bad.
    Yes, it can be a common occurrence. Most likely the crawlspace is drawing in the warmer more humid air. It might be best to close off the crawlspace vents, and it might not make any difference. It just needs to be tried to see what happens. Every single home is differant and what works with one might not work with the other.

    Wet insulation does not insulate very well, so if the insulation is as wet as you say it should be replaced once the problem is solved.

    The beauty of being a home inspector is that we do not and should not design the repair or correction for a problem. We should point the client toward the proper professional that can take care of the issue. More inspectors get into trouble by trying to be helpful and designing the repair or correction.

    An unscientific test on condensation:
    Get your favorite already cold bottled beverage, wrap two sheets of paper towels around it. Then cover it with a wrap of aluminum foil and place it in the refrigerator for about an hour or so. Then take it out and place it outside in the shade. Does the bottle sweat? I bet it does... This is basically what is happening to the air duct.

    Last edited by Scott Patterson; 08-30-2010 at 02:42 PM.
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    Default Re: excessive moisture on duct system.

    The conditions in the crawlspace should be corrected along with the insulation on the duct work.

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    Default Re: excessive moisture on duct system.

    "we do not and should not design the repair or correction for a problem. We should point the client toward the proper professional that can take care of the issue. More inspectors get into trouble by trying to be helpful and designing the repair or correction."

    That bears repeating
    I've added bold to the most important sections

    "we do not and should not design the repair or correction for a problem. We should point the client toward the proper professional that can take care of the issue. More inspectors get into trouble by trying to be helpful and designing the repair or correction."

    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

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    Default Re: excessive moisture on duct system.

    Maybe I'm reading this wrong but it sounds like there is water INSIDE the vapor barrier and pours out when cut, in which case either the vapor barrier has massive leaks or the water is from a different source, maybe the evaporator coil.
    The whole purpose of a vapor barrier on ducts is to keep water vapor away from the insulation... something is not right. Report what you saw in detail and defer to an a/c guy.

    Jim Luttrall
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  12. #12
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    Default Re: excessive moisture on duct system.

    The insulation once saturated no longer provides required R -value. Saturation of insulation could be caused by many issues, not the least of which is condensation. Once the insulation has been comprimised it should be removed, the reason for compromise discovered and, the situation remediated. Crawlspace duct should be insulated with R-8 minimum.


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    Default Re: excessive moisture on duct system.

    Unsealed ductwork will send conditioned air traveling between the duct surface and insulation that is well below the dewpoint temperature of any crawlspace.

    I have never seen a wrap insulation job that had a completely sealed vapor barrier; too much work and attention to detail required to accomplish it.

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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Jim Luttrall View Post
    Maybe I'm reading this wrong but it sounds like there is water INSIDE the vapor barrier and pours out when cut, in which case either the vapor barrier has massive leaks or the water is from a different source, maybe the evaporator coil.
    The whole purpose of a vapor barrier on ducts is to keep water vapor away from the insulation... something is not right. Report what you saw in detail and defer to an a/c guy.
    That's the way I read it too, as did:

    Quote Originally Posted by David Bell View Post
    The insulation once saturated no longer provides required R -value. Saturation of insulation could be caused by many issues, not the least of which is condensation. Once the insulation has been comprimised it should be removed, the reason for compromise discovered and, the situation remediated. Crawlspace duct should be insulated with R-8 minimum.
    Quote Originally Posted by DavidR View Post
    Unsealed ductwork will send conditioned air traveling between the duct surface and insulation that is well below the dewpoint temperature of any crawlspace.

    I have never seen a wrap insulation job that had a completely sealed vapor barrier; too much work and attention to detail required to accomplish it.
    My stumbling block is this wording "the duct system insulated wrap" ... are the duct metal, then insulated and wrapped in the field? Or is that referring to insulated flexible duct which are 'wrapped' at the factory?

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  15. #15
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    Default Re: excessive moisture on duct system.

    About the only time I see an entire duct system wet like the OP described is when the house is already cool and the discharge air temperature gets extremely low. If the air in the ductwork gets in the 40's the extreme temp difference in the duct and the crawl space temp can cause excessive condensation on the outside of the inner duct. This seems to only happen when the A/C is not functioning properly and is over cooling.


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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by James Duffin View Post
    About the only time I see an entire duct system wet like the OP described is when the house is already cool and the discharge air temperature gets extremely low. If the air in the ductwork gets in the 40's the extreme temp difference in the duct and the crawl space temp can cause excessive condensation on the outside of the inner duct. This seems to only happen when the A/C is not functioning properly and is over cooling.
    If the air in the duct is below 50 there are other issues. I am still wagering on water other than duct condensation.


  17. #17
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    Default Re: excessive moisture on duct system.

    This is a hard round duct system wrapped with with duct wrap (silver shiney foil backed insulation), not factory made flex duct. I'm guessing along with others that the end joints are not sealed properly aswell as the long joints. I havent inspected a large enough area to determine if mastic was used. The air handler is also really sweating pretty bad. It actually has mold growth on it and on the wires around it. Im gonna suggest to close off the vents to try to limit the humid air getting into the crawl space. I really appreciate all the replies. Thanks again


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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    This is a hard round duct system wrapped with with duct wrap (silver shiney foil backed insulation), not factory made flex duct. I'm guessing along with others that the end joints are not sealed properly aswell as the long joints. I havent inspected a large enough area to determine if mastic was used. The air handler is also really sweating pretty bad. It actually has mold growth on it and on the wires around it. Im gonna suggest to close off the vents to try to limit the humid air getting into the crawl space. I really appreciate all the replies. Thanks again
    I don't know if I would make that recommendation at this time.

    I think that it would be prudent to advise the owners to seek the help of a mechanical contractor or a person who specializes in residental air ducts and systems. I see just too many variables to not call in a specialist.

    Scott Patterson, ACI
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Patterson View Post
    I don't know if I would make that recommendation at this time.

    I think that it would be prudent to advise the owners to seek the help of a mechanical contractor or a person who specializes in residental air ducts and systems. I see just too many variables to not call in a specialist.
    Bingo! As a home inspector you have to know your limits. Trying to "best-guess" a solution could come back to bite you.

    Bottom line is you see a problem, advise that a specialist look at it.


  20. #20
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Rod Butler View Post
    Bingo! As a home inspector you have to know your limits. Trying to "best-guess" a solution could come back to bite you.

    Bottom line is you see a problem, advise that a specialist look at it.
    They have contacted the HVAC contractor who installed it 5 years ago. I will update with their opinon as soon as i hear. Thanks again for the help


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    Default Re: excessive moisture on duct system.

    I just had one of these yesterday. The house had about 5 return filters and all were clogged. This causes very cold air in the ducts under the house and excess condensation dripping everywhere. The crawlspace also had some areas with poor ventilation and some missing vapor barrier on the ground.

    The other comment above about closing up the crawlspace would be a disaster in this part of the country. The only way you can close one up is to have a professsionally installed sealed/conditioned crawlspace installed. If this is not done and the vents just closed up you will have $15k- $25k in damages within a few years on the majority of the homes. Some HVAC guy had been telling people to close their vents and caused massive destruction to the houses where the owners followed the bad advice.

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  22. #22
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Bruce King View Post
    I just had one of these yesterday. The house had about 5 return filters and all were clogged. This causes very cold air in the ducts under the house and excess condensation dripping everywhere. The crawlspace also had some areas with poor ventilation and some missing vapor barrier on the ground.

    The other comment above about closing up the crawlspace would be a disaster in this part of the country. The only way you can close one up is to have a professsionally installed sealed/conditioned crawlspace installed. If this is not done and the vents just closed up you will have $15k- $25k in damages within a few years on the majority of the homes. Some HVAC guy had been telling people to close their vents and caused massive destruction to the houses where the owners followed the bad advice.

    guess were back to square one. Well in my opinon the HVAC guy did a poor install and should be liable. Now whether the home owner wants to persue legal action, i cant say. But i do know that i would remove all insulation and check the entire system closely. But utilmately its the HO decision.


  23. #23
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    Default Re: excessive moisture on duct system.

    By chance did you take a temp reading on the air leaving the registers?


  24. #24
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by James Duffin View Post
    By chance did you take a temp reading on the air leaving the registers?
    No i didnt, but can this afternoon. I spoke with the HO, he said the contractor had been out and looked at everything and told him it was fine. He just needed to add a fan.

    Sounds like a ine of BS to me. time for a second opinon...


  25. #25
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    Default Re: excessive moisture on duct system.

    If you can be sure and let it run as long as you can before taking your reading and also check to see if the AHU and duct work is still sweating like it was before. The HVAC guy may have done something and just not advertised what he did....especialilty if he did the original installation. I'm thinking along the lines of what Bruce said...it could have been an easy fix but that does not help the problem with the saturated insulation so the HVAC guy is just trying to avoid a problem with the idea the less said the better. That works some of the time.


  26. #26
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    No i didnt, but can this afternoon. I spoke with the HO, he said the contractor had been out and looked at everything and told him it was fine. He just needed to add a fan.

    Sounds like a ine of BS to me. time for a second opinon...
    Tell them to not put a fan in the crawlspace! The fan will only suck in more hot/humid air into the crawlspace. This is the wrong thing to do.

    Scott Patterson, ACI
    Spring Hill, TN
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  27. #27
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    Default Re: excessive moisture on duct system.

    Get rid of the metal leaky duct work and install flex duct. Make sure the ends are seals properly and it should take care of the problem..

    As far as closes the vents off ?????????????????? Why on earth would you want to do that. Sealing up exiting structures is not as easy as it sounds. The home itself was more than likely not built for such a move. How much moisture in the soil in the crawl. Probably quite a bit.

    As far as a fan in the crawl it is a wide idea. Set it up on a humidistat so it only comes on when X amount of moisture it detected. The theory of why draw humid air in from the outside does not hold water. There is obviously already a lot of moisture in the crawl to begin with. A smooth flow of air thru the crawl until the moisture in the air drops (what they are all about) to a reasonable amount.....pretty smart idea. I have seen and installed fans in crawl in extremely humid areas. They work just fine. They only come on when the limit you set kicks it on. When lowered they shut off.


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    Default Re: excessive moisture on duct system.


  29. #29
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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Raymond Wand View Post
    Pretty much

    I have looked at that and countless other articles. The ground and ground water below, how well the drainage of the property is, is the home set up for an enclosed and sealed crawl space. how much leakage to the home. and an absolute countless amount of questions and answers and time of year etc etc etc. Weather conditions outside of course play a big roll. As far as the fan assisted ventilation this is set up on a humidistat and ONLY comes on when levels rise beyond a certain point and shut off below a certain point. It is not the answer to all but I have seen so much more harm than good come out of closing up crawls. Yes there are countless that have no adverse affect but balanced out the vast majority that get closed off just for the sake of doing so causing so much more harm than good.

    Take a crawl that is sealed off. The home owners believe that all problems are solved. A leak starts and a year down the road there is rot everywhere along with a whole lot of wonderful smelling moldy nasty stuff. Sealing a crawl is a wonderful idea.....if the property and home are conducive for such and if it is monitored as it should be. But it never is.

    If it is wet in the crawl............it has to be dried and vented properly. If one just closes off the vents they are asking for serious repercussions over time.


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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    This is a hard round duct system wrapped with with duct wrap (silver shiney foil backed insulation),

    Two guesses: 1) the insulation wrap is not the proper R-value; 2) the insulation wrap is too tight, crushing the insulation, which reduces the R-value.

    Add those to your list of "might be" items.

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  31. #31
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    Default Re: excessive moisture on duct system.

    Just wanted to let you guys know how this turned out. The orginal contractor who installed the system came out and said all crawl spaces have this issue and nothing is wrong.

    the HO hired another contractor to inspect and make recommendation and he said the same thing, but suggested that he add a fan to help ventilate the crawlspace. I dont think these are good ideas, but i'm staying out of it.


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    Default Re: excessive moisture on duct system.

    Quote Originally Posted by Scott Lee View Post
    Just wanted to let you guys know how this turned out. The orginal contractor who installed the system came out and said all crawl spaces have this issue and nothing is wrong.

    the HO hired another contractor to inspect and make recommendation and he said the same thing, but suggested that he add a fan to help ventilate the crawlspace. I dont think these are good ideas, but i'm staying out of it.
    Thanks for the update, it's always nice to hear how things turned out.




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