Q&A / 

Water in Heating Ducts

DEAR TIM: My husband and I live in a one-story home built on a slab. The home was built 30 years ago and we are the fourth owners. A few days ago I heard a bubbling noise coming from one of the floor heating vents. I looked inside the vent and there was standing water! We pumped out water for two hours but the vents filled back up. Where is the water coming from? How can we stop it? Do you think this problem was known by the previous owner and if so, do we have any recourse? Lynn F., Norcross, GA

DEAR LYNN: Oh my goodness. You have got a serious problem or two. This sub-surface water can not only cause enormous problems for people who own slabs, but those who have houses on crawlspaces and those built with full basements. Many people who own a slab house think they are immune to problems caused by subsurface water. But I can't begin to tell you how many emails I receive from people who have your identical problem: flooded buried heating and cooling ducts.

Use a wet-dry vacuum to suck out water from the ducts under a concrete slab. PHOTO BY: Tim Carter

Use a wet-dry vacuum to suck out water from the ducts under a concrete slab. PHOTO BY: Tim Carter

The problem is happening because water often moves sideways through soil instead of straight down. If you lived in parts of Florida or other parts of the USA where the soil is extremely sandy and drains like water passing through a cooking colander, we would not be having this conversation. But my guess is that your home is built on soil that has a certain percentage of clay.

When rainwater falls onto the ground it readily passes through the topsoil as this upper level of the soil frequently contains lots of air voids. But as you go deeper into clay soils, the soil becomes extremely dense and often water is blocked from going down. The water then starts to move sideways through the soil always flowing downhill and often pops to the surface as a spring. This water is the fuel that creates creeks, streams and rivers.

If you look outside your home and imagine the vast amount of soil that might be higher in elevation than your house, you might be amazed to learn that there are hundreds of thousands of gallons of water in the soil much of which is moving directly towards your home. This water can easily find its way under the slab and into the ductwork beneath the slab. It is no wonder the vents filled back up after you pumped them out.

Anyone who suffers from subsurface water that is invading any part of a house can stop it in almost all cases by capturing the water outdoors and then redirecting this water to the lowest part of the lot. Think of how gutters work on the roof of a house. Gutters capture the vast amount of water on a roof, channel it to various outlet holes within the gutter and then this water is piped away from the roof. Ideally rainwater from a roof should be piped far away from a house and not be allowed to drop out of downspouts onto simple splash blocks adjacent to a foundation.

You can capture the subsurface water by digging a trench around the outside of your home. This trench should be placed about 6 to 8-feet away from the edge of your home. Dig this trench 6 inches wide and between 18 to 24 inches deep. The bottom of the trench should be parallel with the soil as it goes around your home. The trench should be extended away from the house and needs to end up at or near the lowest point of elevation on your building lot.

As the trench starts away from the house, make the bottom of the trench nearly level. As the ground falls away from the house, the trench will become shallower and eventually the bottom of the trench will be level with the top of the soil.

You place a 1 or 2-inch layer of washed 1-inch diameter gravel in the bottom of the trench and then place a 4-inch diameter perforated pipe in the trench. Fill the trench with more 1-inch washed gravel until you are within 1 or 2 inches of the top of the trench. You can place pieces of sod over the gravel.

The subsurface water will now pass through the soil and enter the trench. Because it is easier to pass through gravel instead of soil, the water will drop down to the pipe. There it will enter the pipe and be transported rapidly away from your home to the lowest part of your lot. The underside of your slab will never be saturated with water again.

If your state has a property disclosure law and the previous owners knew of this serious defect, they may have been obligated to bring this flaw to your attention. You should call the Realtor you used in the transaction to see if there was a property disclosure form that was not given to you.

You can also call your local fire department. Just about every fire department in the nation keeps very good records of each time they leave the station and are asked to put out a fire or help in a situation. If they were ever called to the house to help pump out the vents, you know the previous owner knew there was a problem. Well there is always the possibility your local fire department has mystic extra-sensory-perception powers!

Water in buried heating and cooling ducts can cause serious health problems. The water in the ducts can initiate the growth of mold. Each time the heating or cooling system operates, the air moving through the ducts can blast millions of mold spores throughout the house.

Although expensive to do, it might be a good idea to investigate the feasibility of moving the ducts into the attic space. The one-time expense may be a great way to protect the health of you and your family.

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10 Responses to Water in Heating Ducts

  1. I am having a serious problem with this same issue. We have pumped over 2300 gallons out of our floor vents. How will this trench prevent water from draining down to the weeping tile which is higher then vents. Our house is the lowest point of our yard and we don't have a way to flow water away since it travels back to the foundation. We have a bungalow style home with a walkout basement and the whole yard is 4 feet above That??? Please we are desperate

  2. Tim, I had this problem too. A combo of foundation sealer (ThoroSeal, their best stuff in a green bag applied 2x, and I used their liquid chemical additive for best results) and replacing the drain tile outside the house (gravel surrounding it was nearly 100% plugged up is what I found out) seems to have finally fixed it. I knew where the water was coming in (roughly) so that helped a bit. There is a company that will seal the duct work from the inside, they may just be local to me but FWIW there may be others out there, and they may be cheaper than relocating the duct work to the attic if their process actually works. The before and after picture on their site look pretty good.

    http://www.ductwhip.com/airductrestoration_process.htm

    On to my current problem: Not only is my duct work in the slab, but the builders routed the heat from the duct work to where the water lines enter near the bathtub to keep the lines from freezing, since the bathroom is along an outside wall. The problem is that heat rises up and melts the winter snow on the roof for the recess / wall cavity the bathtub is in at the very front of the house (more in a bit). The condensation that forms on the interior of the roof then drips down the inside front of the exterior clapboard. It is not a huge problem, but if we have a heavy snow winter, it can lead to water damage because it has been doing this for 20 years now (I never really understood the problem until about a year or 2 ago, and initially thought it was simply a roof leak (new roof done 7 years ago), and for the first 5 years didn't know I even had a problem).

    Can you think of any way to keep that heat from rising up ? I have a few ideas but won't bounce those off of you as to not bias you. I do need much more attic insulation, but the heat itself travel up the uninsulated stud spaces along the exterior wall.

    thx ... Ron

  3. Hi, our pipes were almost frozen this morning so I turned on the bathtub at a trickle placed a bucket in there to catch the water for toilets. We went to church. Hours later the bathtub was over flown and water was running down my heater vent. Ever since the other side of the house the vents are blowing cold air instead of warm. It's below 20s out side. How do we get rid of the water? Do you think it's frozen? There is a crawl space. Who do we call or can we do this ourselves. It's a manufactured home we are renting.

    • Ann, you call the owner first. Then you call a heating serviceman to get heat going again. You tell the owner he's got to do what's necessary so that the pipes don't freeze. NEVER leave a house with water running. What a mistake that was, but I'm sure you realize that now.

  4. Hi, our plumbing was backed up and water ran over from toilets and filled heat ducts in both bathrooms in mobile home. No heat comes out from either vent now? What should we do? Thanks

  5. I closed on my home november 2012. Recently I began noticing my home smelled like stale water and that several of the walls has substantial condensation, and just about all the windows in my home are heavily condensated.
    I am in the process of having the roof replaced even though my provate home inspector said the roof was oaky and should last me about 5+ years......the roofing company went around the enitre house and the city inspector yesterday they told me they believe that there may be water in the ducts of my home, which is on a slab. where do I begin with this....who do I call to verify this? By the way I live in Michigan.

  6. My friend has a serious water issue in her rented home. I walk in and it feels damp. She knows she's had a problem with water problems in her vents before but I think the owner just sweet talks them too much and she thinks its ok. I was In her room tonight and heard water bubbling and making a lot of noise in her floor vents. What do I do or tell her?!

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