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Thread: Humidifier Drain and AC Overflow Problem

  1. #1
    DIY Member SAS's Avatar
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    Default Humidifier Drain and AC Overflow Problem

    I just moved into a new (new to me, that is) house and discovered that turning on the furnace mounted humidifier floods the basement floor. Name:  2014-02-03 20.55.59.jpg
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    The first picture shows how the humidifier overflow is configured. At first I thought that one of the fittings was leaking, but in fact it's just that the water doesn't move through that "trap" quickly enough. It's a flow through humidifier and sometimes the water flow overflows the top of that open PVC pipe. I'm wondering why the traps are there anyway. Here's where the pipe connects to the drain line:Name:  2014-02-03 20.57.14.jpg
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    As you can see it is sitting in that drain pipe with plenty of air space around it. If the traps are to prevent sewer gas, they won't server any purpose here. I'm assuming that there is a trap under the floor, but I have no way to verify it except that there is no smell. (The other line that connects in is a condensate drain from an upstairs air conditioning unit.)

    Could I just cut the section above the furnace out and replace it with a 90 degree off the AC condensate pipe and an open T into which I put the plastic tubing from the humidifier?

  2. #2
    DIY Senior Member Reach4's Avatar
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    Re-thought...
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    Last edited by Reach4; 02-03-2014 at 08:49 PM.

  3. #3
    DIY Member SAS's Avatar
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    Do I really need an air gap? Isn't that to prevent backflow? If so, doesn't the airgap where the humifier tube enters the pipe suffice?

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    DIY Senior Member Smooky's Avatar
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    It may be slime that is clogging up the lines. You could construct them so they are easier to clean. If the drain line is not connected directly to the sewer line you may not need the p-trap for the humidifier but sometimes the water in the p-trap is needed to maintain positive pressure in the ac unit.


    https://www.google.com/search?q=p-tr...2F%3B882%3B525

  5. #5
    DIY Member SAS's Avatar
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    Thanks, I didn't know that about the Air Conditioner condensate line. I can leave that trap alone. I'll make sure the line is clean when I take out the other trap. I did snake the trap for the humidifier, but depending upon how quickly the water runs out, it can just overflow that tube. The trap provides too much resistance to the water flow.

    Do you know of any reason I would need the trap at the humidifier? Does the idea of just turning that T 90 degrees and dropping the plastic tubing into it sound OK?

  6. #6
    DIY Senior Member Smooky's Avatar
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    You could try it and see. I think that would be ok. I would make it taller so it doesn't overflow so easy.

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    DIY Senior Member Reach4's Avatar
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    It seems to me that I have a few times seen the line from a condenser come out to a tee. The top of the tee is open, and the bottom has a down pipe. I can't say why. That is why I was considering that a vent would be in order. Maybe it was that way to make it really easy to put a snake into. A vent sure isn't going to be good if you need positive pressure.

    The slime idea makes sense. I might consider pouring some Clorox solution in there if I were not afraid of overflowing. Maybe stop the humidifier for a bit to let that work its way through.
    Last edited by Reach4; 02-03-2014 at 08:50 PM.

  8. #8
    In the trades Dana's Avatar
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    The best solution to air-handler mounted humidifiers is to decommission them, and air seal both the ducts & house to where you don't NEED to add humidity to the indoor air. In a CT climate a house that meets IRC 2012 code-minimum for air tightness (3 air exchanges per hour at 50 pascals) will never need active humidification, and in some cases would need active ventilation to keep indoor humidity levels under 40% RH in winter.

    Humidifiers can lead to mold issues inside your walls if not used judiciously. Humidify to no more than 35% RH @ 70F in winter or you'll end up with high mold-spore counts in your indoor air come springtime. The stored up moisture in the building materials becomes the sauce on the mold-food cellulosic materials (wood, paper facers, etc.) in the exterior wall assemblies. The healthy-comfortable zone for humans is 30-50% RH, but it's healthier for the house to keep it on the low side in winter. Any wood in the walls/ceiling that averages below the dew point of the interior air takes on moisture in the form of adsorb over the winter, then when it warms up to where molds can reproduce rapidly they go nuts. The dew point of 35% RH/70F air is about 41.2F, which means even in a CT winter there will be significant numbers of drying hours, since the outdoor air will often run that high or higher. But 50% RH/70F air has a dew-point of 50.6F, which means almost no winter-time drying, and the sheathing & cool half of the studs will just keep collecting moisture from November-March, leading to a far, far greater moisture burden.

    The drain trap open to the air like that are prone to developing slime-molds, as are condensate drains. Having to clean them out every few years isn't an uncommon issue. A bleach solution alone may or may not do the trick- I've had to ream the gunk out with piece of wire to re-establish flow on a condensate drain more than once.

  9. #9
    DIY Member SAS's Avatar
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    So I decided to just replace the trap for the humidifier with a new tee. When I took the old one out, it was pretty clean. Certainly nothing was blocking the water flow. The way that trap was constructed with 3/4 inch PVC just didn't allow enough flow. Here's the new configuration.
    Name:  2014-02-04 21.39.41.jpg
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    Re-reading some comments, I decided I should add a short vertical piece of pvc just in case the water backs up a bit. I didn't think it was worth another picture.
    Last edited by SAS; 02-04-2014 at 07:18 PM.

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    DIY Junior Member 6t7gto's Avatar
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    Oh come on. We like pics.

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    DIY Senior Member Rich B's Avatar
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    I would have removed the tee entirely in that horizontal pipe run. Extend the clear plastic line down to the drain pipe. Install a tee or a santee type fitting in the vertical run if possible.....No way that would back up....Lots of plastic fittings out there to make that clear plastic line connect to the PVC and just slip on and clamp it..
    I have a similar humidifier.....I installed it....drains into a condensate pump and is pumped to a washer standpipe.......Pump is also for my nat gas furnace condensate and ac condensate.....

  12. #12
    DIY Member SAS's Avatar
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    Quote Originally Posted by Rich B View Post
    I would have removed the tee entirely in that horizontal pipe run. Extend the clear plastic line down to the drain pipe. Install a tee or a santee type fitting in the vertical run if possible.....No way that would back up....Lots of plastic fittings out there to make that clear plastic line connect to the PVC and just slip on and clamp it..
    I have a similar humidifier.....I installed it....drains into a condensate pump and is pumped to a washer standpipe.......Pump is also for my nat gas furnace condensate and ac condensate.....
    My former house had the arrangement that you have. It worked great until the day the pump float got stuck. I do like your idea about running the tubing over to the vertical section of the drain pipe and installing it there. Too bad you didn't suggest it sooner! It's working fine now, so I'm closing shop on this one.

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    DIY Senior Member Rich B's Avatar
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    I have lived in the same house for 42 years. Never had more than a puddle in the basement and in just one spot where the floor is low. No sump pump and no floor drain. I always had a condensate pump for the AC and never had a problem with it. It is actually a 2 family home and has 2 separate furnaces and AC units.....

    I replaced the furnaces with high efficiency multi stage condensing furnaces. I punched thru the concrete floor and just allowed the water to drain under the slab. Worked fine for years.

    A few years ago we had weeks of heavy rain. The ground became so saturated water came in the basement anywhere there was an opening in the floor or side walls at the bottom row of blocks. I had about 4-5 inches of water in both basements and it happened twice in one week. I pumped water out of those basements for days as did most everyone in the area.

    Since then I closed up anything that could weep water and used hydraulic cement along the lower row of blocks and drylock paint.

    New condensate pumps and all 3 drains go into them. I had to drop the pump down to the floor.

    If we ever had another period of rain like that one I am sure I would still see some water but far less hopefully.

    Once in 42 years is fine with me.....Damage was limited to just junk laying around down there....Cardboard boxes, wood....and mostly just stuff that needed to be thrown out anyway...

  14. #14
    DIY Member SAS's Avatar
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    I agree that the condensate pump is a fine solution. In my former house we had two because we had two furnaces. Only once in 27 years did I have a problem. What I discovered when it did cause some puddling in the basement was that the float became stuck because of a combination of slime and scale. My advice would be to check the pumps periodically to make sure that they're clean.

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