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  1. #1

    Confused Under Slab Duct Question

    My son is buying a house in Oklahoma City. The ductwork is under the slab. During the inspection, the inspector cited that there is rust on the vent boots and some sand at the bottom of the boot. I really dont know anything about this type of duct work. Can anyone comment on the reliability of the duct work and what conditions may have caused the rust on the boots? The seller is paying for a scope tomorrow to demonstrate that the ducts are ok, but I would like to be smart enough to ask the right questions.

  2. #2
    Join Date
    Jun 2006
    Posts
    491
    typically, the condition that you described is just what it appears to be - the ductwork rusted thru and is now exposed to the earth below the house.

    that can create other problems such as groundwater entering the ductwork (being exposed to moisture on either side of the duct could have rusted it thru meaning groundwater could be the cause and not the effect). possible infiltration of pest into your ductwork. indoor air quality problems. possibly/probably other reasons.

    how old is the equipment (the furnace or air handler and the evaporator coil) in the house? how much space is in the attic?

    i ask these things as it is common when replacing downflow equipment to install upflow equipment in its place and install new ductwork in the attic doing away with the previous layout.

    sometimes what originally was the supply ductwork is used with an upflow unit when it is installed but functioning instead as the return ductwork. this can work well but it's important the ducts are in good shape or can be put into good shape.

    there is a process that is available that coats your ductwork and is supposed seal it up and put it back into good shape and keep it that way but i don't have any direct experience with that to say one way or the other.

    its important that the person doing the duct inspection be a neutral party and i would think it would be correct for a camera to be ran thru the ducts and displayed on a moniter so everyone gets to see what problems either do or don't exist.

    get back with us tomorrow and let us know what the inspector says after looking at the ductwork closer if you have any questions about the findings and/or recommendations being made.

    .

  3. #3

    Update

    ok. here is what was found. All of the vent boots are rusted out. The recommendation was to resleeve the boots. Also 3 t-fittings under the slab with extreme rust and small holes. Two vent connections where the vent connects to the plenum were rusted out. The report says that the damage was likely from ground water due to lack of gutters or sudden large amount of water from a plumbing leak entering the ducts.

    There is room in the attic to redirect to an upflow duct system. The report is going to be used by the homeowner to determine whether to fix? the ductwork or redo the duct work.

    Can you really fix the ducts? and if you do, isn't there a likelihood that the same thing may happen again, even if the gutter issue was resolved?? It also seems that even if you could get into the slab to fix the tee's and connections, that you would have to do some major excavation and repair of the slab ??wouldnt that be a huge cost in comparison to altering the system to an upflow system?

  4. #4
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,348
    I have seen a lot of these issues and having the existing boots sealed off and new equipment and ductwork installed is the only logical solution.

    The sealeant mentioned can work if damage is minimal but there is a water problem to be dealt with i.e. french drain.


    edit: don't ever bust up the slab and risk loosing structural stability. Especially knowing you have water buildup.
    Last edited by captube; 08-13-2008 at 09:59 PM.

  5. #5
    Join Date
    Jul 2008
    Location
    Poestenkill, NY
    Posts
    769
    I think the gutter thing is a red harring. Gutters on a roof are not going to stop the forces of nature - be it manifested as heavy rains, hydrostatic pressure, poor drainage, etc, etc, etc. I think people put too much faith in what gutters really do - which is to say they have a rather insignificant effect on water movement below grade.

    I'm in a northern climate, so in-slab ductwork is very foriegn to me - but I would think it's very problomatic(!), and often abandoned for an upflow system sometime down the road as mentioned?! I don't want to scare you though - maybe it can work for many years if installed or fixed correctly, but I'm skeptical...

    Of course, I don't care for ducting in attics either - but that's a very common practice. If I were a bird on your son's shoulder, I'd whisper, "get a house with a basement". But they're not too common in your area?

  6. #6

    Thanks

    Thank you both for your comments and advice. Based on your thoughts and my paranoia over these problems, my advice to my son is to demand that the ductwork be redirected to the attic or walk from the deal. I'm no expert on any of this stuff, but jackhammerring the slab to get to the t's seems to ripe for creating other problems. (and I agree that it sure seems as though it could cause potential structural issues).

    I have heard mention of this coating inside the ducts, but everyone that has mentioned it says they don't know much about it. I did the google thing and there is minimal information on the process and it all seems to be relatively new. That worries me.

    Soooo. Unless anyone here tells me I'm off base, this decision by the existing homeowner will be a make or break for the deal. I don't want my son walking into something that is going to cost him alot of $$ downstream when it can be fixed for good now. Thanks again for the advice. Im glad I found this forum.

  7. #7
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,348
    Here is a link on coating info. http://pezsondemo.com/coating_process.html

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