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Thread: Trapping an air handler

  1. #1
    DIY Member Lightwave's Avatar
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    Default Trapping an air handler

    What's the appropriate way to trap a (residential) air handler condensate drain so it doesn't pull sewer gases into the house during heating season? This is a pull-through air handler: the condensate line is under negative pressure when the fan is running.

    The 'professionals' who installed my AH installed a P-trap on the air handler, which is directly plumbed into the drain for a seldom-used laundry room sink, upstream of the sink trap. Needless to say, during heating season I have to run the sink every few days to prevent the trap from drying out and allowing sewer gas into the house.

    Is there a more permanent solution here?

  2. #2
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    don't pipe it to the sewer, pipe it outside.

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    Plumbing Designer FloridaOrange's Avatar
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    Quote Originally Posted by Peter Griffin View Post
    don't pipe it to the sewer, pipe it outside.
    I agree. Under all codes thar I am aware of condensate can NOT be directly attached to sanitary.
    Matt
    Semi-professional plumbing designer
    Enjoying life in SW Florida

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    Plumber jimbo's Avatar
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    Quote Originally Posted by FloridaOrange View Post
    I agree. Under all codes thar I am aware of condensate can NOT be directly attached to sanitary.
    It is quite comnon around here to connect it to a wye connector ABOVE the trap under a lav sink. This is an indirect drain. It seems the problem the poster has is with the vacuum on the drain line, which I am confused about, and that vacuum may be drying out his trap. In this situation, I do agree that it needs to be removed from the sanitary drain, and pumped outside.

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    Moderator & Master Plumber hj's Avatar
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    Default trap

    The proper way to trap it is to NOT connect it to the sewer system directly. It MUST either drain to the exterior or the drain line is connected AHEAD of the trap in some fixture that has frequent use. There is NO way to trap the discharge and NOT pull sewer gases, because there is little, if any, condensation in the wintertime to keep it sealed. AND if the trap is not designed for the amount of negative pressure the gases would be pulled through the trap even if it did have water in it.

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    DIY Member Lightwave's Avatar
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    The condensate line is under negative pressure because it's coming from an air handler rather than an AC coil mounted over a furnace. Air handlers mount the AC coil before the fan. In this case, there is about .3" WC of vacuum on the condensate line.

    The heating contractor who installed the AH tied the condensate line into the sewer via a laundry room sink. The condensate line It's piped in ahead of the trap but the trap dries out because the sink is very rarely used.

    To add insult to injury, the connection on the AH for the condensate line is below the flood level of the sink....

    I don't have a good place to dump condensate outside as there's a patio in the way. The best idea so far seems to be to pump the condensate into the laundry standpipe via an indirect connection. Good idea/bad idea?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    A condensate pump is a very common way to run it...mine is that way as well as most of my neighbors. Mine is actually on my boiler...I run my a/c condensate drain outside, but the boiler can't because it would freeze up and create a bad safety hazard.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member Lightwave's Avatar
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    Thanks for everybody's input so far.

    I've been thinking about how to rework the condensate drain to use a condensate pump. Unfortunately, I haven't found enough data on condensate pumps to figure out which (if any) can pump against 1" of vacuum, nor have I found a condensate pump that accepts side input.

    Will the plan below work to prevent the air handler's suction from interfering with the pump and direct condensate to a top-input pump without being an S trap?


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    Moderator & Master Plumber hj's Avatar
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    Default pump

    The pump does NOT pump against a negative pressure. The water drains into the pump and then the pump discharges the water to the drain. As a matter of information, the connection being below the flood rim of the sink would ONLY be a factor if the connection to the air conditioner were also below it, so that a backflow from the sink could overflow into the air conditioner.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    Default air handler

    The negative pressure in the air handler is usually expressed in "inches of water column". IF your "trap, the measurement shown as 1" minimum, is not GREATER than that number, the air handler will still draw air past the trap. But with the pump it will just draw room air through your "vent/antisiphon" tee.

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    Architect Spaceman Spiff's Avatar
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    I'd install a condensate pump and then run a vinyl tube to drop into the basin of your laundry tub or a floor drain. That will help keep the drain or laundry tub trap primed and gives you the air gap required. Also the pump will pump up to 8' of vertical head in most cases or 30' runs. With that kind of run you could pump it outside somewhere convienient.
    Spaceman Spiff aka Mike

  12. #12
    DIY Member Lightwave's Avatar
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    Quote Originally Posted by hj View Post
    As a matter of information, the connection being below the flood rim of the sink would ONLY be a factor if the connection to the air conditioner were also below it, so that a backflow from the sink could overflow into the air conditioner.
    That's what I'm saying. The connection on the AHU is below the flood rim of the sink.

    The negative pressure in the air handler is usually expressed in "inches of water column". IF your "trap, the measurement shown as 1" minimum, is not GREATER than that number, the air handler will still draw air past the trap.
    Maximum negative pressure on this AHU is 0.7" wc. In our application we get about .3" wc.

    I designed the trap depth based on data I found at http://hpac.com/mag/condensate_traps_brusha/

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