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Water in slab dryer vent

| Posted in General Discussion on May 16, 2002 08:10am

My three-year-old home is on a slab.  The dryer vent runs about 20 feet .  It runs from the laundry room, under the slab beneath the garage, to vent outside.  Clear water is in the line and I must wet vac to suck it out each time before I use the dryer.  I don’t know if I get all the water out each time.  (Time factor)   About a gallon of water removed each time seems to be enough to let the air blow through the vent so that I no longer  hear a “Glug, glug” from the vent or see the water lapping in the bend or create a sauna out of my dryer.  What do you thing is the problem and needs to be done?

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Replies

  1. DavidThomas | May 16, 2002 09:40pm | #1

    Almost certainly, the line was not insulated if water is building up that quickly. Whether the duct work runs through the slab itself, the sand base to the slab, or native soils; it has to be insulated.

    And this may be worsened by using the wrong size or type of ductwork. 4" is needed for any long runs. 3", any flexible lengths, and lots of bends all create backpressure and reduce air flow - giving the water more time to condense. The turbulence in bends and small ductwork also increase the heat transfer which is bad - you don't want the dryer exhaust to cool before it exits the building.

    Consider the traditional metal ductwork run through the walls. The metal is thin and the entire ductwork doesn't weigh much. So in the first few minutes (during which some water condenses), the metal comes up to temperature. Then the dryer exhaust can make it outside without more water condensing out and will, especially towards the end of the cycle, evaporate any of that water that condensed earlier.

    Contrast that with the buried ductwork. Sorrounded by such a large mass of soil, the duct work never gets hot. So water continues to condense out during the whole drying cycle. Run a few empty loads would help a bit, but not much, because the soils would continue to cool the exhaust and reduce its ability to carry water vapor.

    You can confirm this is case by checking the temperature at the exhaust vent. It should be quite warm or a little bit hot. Slightly warm doesn't cut it.

    What to do about it? If you recently moved in, go after the sellers for not disclosing a known defect. They had to know about this, right?

    If you had it built for you, it seems a long time has passed to go after the builder. But it should not have been installed this way.

    If you built it, chaulk it to one of those things you'll be better at the next time you build a house.

    Fixes? 1) Mount a shop outside the vent (it can be a pretty small one). Snake a 1"line down the duct work. Run the shop vac when the dryer runs. Sears sells a relay for $20 that is designed to turn on a shop vac when your table saw turns on. If you power your gas (!) dryer through that plug, then the shop vac will come on and off automatically. Then drain the shop vac ever few loads. Or drill a hole and run some 1/2" tubing out to the garden through a swing check valve. Then it will self-drain between loads. Elevate the mounting of the shop vac if you need the water to flow a greater distance.

    2) snake a new duct within the existing one. Not too hard to do if it is a pretty straight run but there are some limitations. A flexible duct of smaller diameter will be more restrictive to air flow. And may be more backpressure than the dryer is designed for. But if the run is short, it would one way to retrofit some insulation, in effect. Because the air gap between the old and new ductwork would help keep the air in the duct warm enough to avoid most condensation. If the duct is too long and/or too narrow then a booster fan (wiring like the shop vac, above) would help keep the air moving.

    3) I hate electric dryers for their long drying times and the higher operational costs. However, an electric dryer would condense less water in your ductwork than a gas dryer. This is because they don't add the water vapor from combusting natural gas, only the water from the clothes. Running any dryer on a low heat will also help. Using more air to dry the clothes (rather than higher heat) will reduce the condensation in the ductwork.

    4) Rent a jackhammer. Get some beer and steaks. Invite some strong friends over. . . .

    Good Luck

    David Thomas   Overlooking Cook Inlet in Kenai, Alaska
    1. alex3sons | May 16, 2002 09:46pm | #2

      Thanks so much for your time and knowledge.  We just bought the house and the builder and his plumber aren't "standing" behind their house.  Why the previous owners apparently had no problems, we don't know.  We moved in in September. We didn't notice the water until December.  We live in Northwest Arkansas. 

      Al(exandra)

      1. User avater
        BillHartmann | May 16, 2002 11:01pm | #3

        Al

        I almost posted a different view from David. But I thought that their was a good chance that he was right.

        But then I saw you other message and after you mentioned that there where springs in the area my guess is that you have a ground water problem. I have heating ducts under my slad and a problem with then filling up with water about once every 2 years.

        Use your wet dry vac and vacum out the duct. Then wait a while and see if water is filling back in the duct. If it is them you have ground water problems.

        1. alex3sons | May 16, 2002 11:16pm | #4

          Will do.  I'll let you know.  Thanks.

        2. Piffin | May 17, 2002 12:22am | #5

          It sounds like ground water problems to me, in which case you'll be installing a sump pump to drain the soil nearby or running a new perimeter drain to daylight in order to give the water somplace else to go.

          Diversion beats distraction in my book.

          Excellence is its own reward!

          1. DavidThomas | May 17, 2002 12:27am | #6

            Wow, that would be some very shallow groundwater, but I agree it is a possibility. A couple of scoops with a shovel should answer the question. If so, start with diverting downspouts well away from the building. FHB had an article on that about 1 year ago.

            David Thomas   Overlooking Cook Inlet in Kenai, Alaska

          2. Piffin | May 17, 2002 02:11am | #7

            I know, it doesn't seem right but I've seen it and, like a posteer said a week ago - "After all, this is Arkansas!"

            ;>)Excellence is its own reward!

          3. User avater
            BillHartmann | May 17, 2002 02:51am | #8

            I don't know if you saw his other thread.

            http://forums.prospero.com/tp-breaktime/messages?msg=20282.1

            When I first saw this, David condensation sounded like it might be the problem. But them I saw the other thread and it makes be think that there is something more serious going on.

          4. Piffin | May 17, 2002 03:00am | #9

            There's a water supply or waste leak here someplace it looks like.Excellence is its own reward!

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