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  1. #1
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    Default How to Seal Existing Ducts In Crawl Space

    I noticed that my ducts in my crawl space are dripping moisture. What is the best way to seal existing duck work?
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  2. #2
    Elite Member CurlyDave's Avatar
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    Default Re: How to Seal Existing Ducts In Crawl Space

    If you are using air conditioning at this time of year it may just be condensation. You might need insulation more than sealing.

    I can't think of any time when the air inside the ducts should have liquid water it it.
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  3. #3
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Duct sealant try you local A/C or sheet metal shop it comes in tube's or cans.

  4. #4
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Quote Originally Posted by CurlyDave View Post
    If you are using air conditioning at this time of year it may just be condensation. You might need insulation more than sealing.

    I can't think of any time when the air inside the ducts should have liquid water it it.

    I'm voting with Dave on this one insulate them

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  5. #5
    Super Star Member Thomas's Avatar
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    Default Re: How to Seal Existing Ducts In Crawl Space

    There insulate spray and tape you could purchase,most good insulaters will say least one inch fiber glass/black foam seal w/contact cement.

  6. #6
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    Default Re: How to Seal Existing Ducts In Crawl Space

    I was thinking that the cool air (AC'd) was leaking out the duct's seams and joints and causing the condensation.

    The ducts are insulated although it is torn in places.
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  7. #7
    Platinum Member rjkobbeman's Avatar
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Quote Originally Posted by dieselscout80 View Post
    I was thinking that the cool air (AC'd) was leaking out the duct's seams and joints and causing the condensation.

    The ducts are insulated although it is torn in places.
    That could be the case, however condensation does not require warm air to contact the "cold air". Warmer, humid air contacting "cold" period causes condensation.

    The cold air inside the ducts cause the ducts themselves to cool down. The relatively warmer humid air surrounding the relatively colder metal ducts cause the condensation.

    Obviously it is best to seal any leaks, however if your cold ducts traverse through warmer humid air spaces, they will cause condensation if they are not insulated.

    Remember, condensation is the extraction of moisture from the air. Cooling down relatively warmer, humid air extracts the moisture from that air.
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  8. #8
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Quote Originally Posted by rjkobbeman View Post
    That could be the case, however condensation does not require warm air to contact the "cold air". Warmer, humid air contacting "cold" period causes condensation.

    The cold air inside the ducts cause the ducts themselves to cool down. The relatively warmer humid air surrounding the relatively colder metal ducts cause the condensation.

    Obviously it is best to seal any leaks, however if your cold ducts traverse through warmer humid air spaces, they will cause condensation if they are not insulated.

    Remember, condensation is the extraction of moisture from the air. Cooling down relatively warmer, humid air extracts the moisture from that air.

    IC said the blind man!

    So fixing the insulation may cure the whole issue...
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  9. #9
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Mastic is what it is called. A air conditioning distributor place (wholesaler) will have it. That sort of stuff they will sell over the counter to anyone.

    Seal up your connections wearing your worst clothes as it gets all over everywhere.

    The hot attic air is mixing with the cold air and causing condensation; often evidenced by water droplets or spots on your register vents. Try and seal around the boots as they are called; thats the things mounted on the ceiling that you screw the grills onto. Cheap stuff and does a lot of good. It can be put on with the cheapest paint brush you can find and wait 2 or 3 hours to firm up. Turn the blower back on and back in business.

    Yes also put some good unfaced insulation around the ducts and anything else related to the ac ductwork.

    Been doing this at my house and really works. I used to have water spots on my registers and dirty streams on the ceiling from pulling in dirty attic air.


    Matt

  10. #10
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    Default Re: How to Seal Existing Ducts In Crawl Space

    Quote Originally Posted by mattcage View Post
    Mastic is what it is called. A air conditioning distributor place (wholesaler) will have it. That sort of stuff they will sell over the counter to anyone.

    Seal up your connections wearing your worst clothes as it gets all over everywhere.

    The hot attic air is mixing with the cold air and causing condensation; often evidenced by water droplets or spots on your register vents. Try and seal around the boots as they are called; thats the things mounted on the ceiling that you screw the grills onto. Cheap stuff and does a lot of good. It can be put on with the cheapest paint brush you can find and wait 2 or 3 hours to firm up. Turn the blower back on and back in business.

    Yes also put some good unfaced insulation around the ducts and anything else related to the ac ductwork.

    Been doing this at my house and really works. I used to have water spots on my registers and dirty streams on the ceiling from pulling in dirty attic air.


    Matt

    Mine are all under the house in the crawl space so no ceiling issues which is a great thing.
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