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Thread: HVAC Condensate Drain Line Question

  1. #1
    DIY Junior Member philwgreen's Avatar
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    Default HVAC Condensate Drain Line Question

    In my continuing effort to inspect (and fix where necessary) the work of the previous homeowner's plumbing - I came across this in the crawl space.

    The HVAC unit is in the attic and the primary condensation line runs through the wall and end up in the crawl space. As you can see in the attached picture, there is a trap coming off of the main stack and the condensation line runs directly into it.

    So, the questions are:

    1. From what I've read, I would think at a minimum there needs to be an air gap between the two right? How big of a gap should there be? Shouldn't there be a flared end (not sure of the technical term) on the top of the pipe running vertically from the trap?

    2. Is the trap and the way it connects to the stack done correctly?

    Thanks for any help in advance!

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  2. #2
    In the Trades Gary Swart's Avatar
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    I'm not a pro, but it looks to me like you have an S trap. Now pros may disagree, but it is my understanding that there must be a vent between the P trap and prior to the line making a downward turn. The 45 you have between the P trap and the main drain makes the S trap. I think the air gap is OK, again keep posted for pros to comment.

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    Moderator & Master Plumber hj's Avatar
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    Your system does NOT put condensation into the trap 365 days a year. THEREFORE, when it is not doing it, the trap seal dries out and your blower draws sewer gas odors into the system and blows them throughout the house. The condensate should either dump on to the ground outside the residence or connect to the sewer system through a trap which DOES have water usage, such as a sink or laundry drain. In the event of a sewer stoppage, ALL the drainage will overflow that trap and flood the crawlspace, but you will not know it has happened until the odor gets overpowering.
    Licensed residential and commercial plumber

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    DIY Junior Member philwgreen's Avatar
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    Just above that trap in the pictures is where the kitchen sink ties into the stack. It wouldn't be a problem to cut into that drain line as it's easily accessible.

    Question is: what kind of fitting do I use? A combo wye with a bushing for the 3/4 drain line?

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    FWIW, the two (maybe more not visible) banded couplers are not allowed above ground, either. They should be reinforced hubless connectors - i.e., a thinner rubber sleeve with a full metal reinforcement band around it. This is to ensure the ends stay aligned and to provide proper support. Also, if the CI isn't well supported above, over time, it could damage the pvc inserted in there - the CI is very heavy, and PVC can't take the weight; it needs to be properly supported. If you were going to dump it into the kitchen sink, you may want to treat it like a garbage disposal - just ensure it has proper slope so stuff doesn't get forced back into it and plug it up since it only has gravity to run the condensate, not a pump like a DW.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    In the Trades Tom Sawyer's Avatar
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    Can you point me to where the code says banded couplings are not allowed above ground.

    705.2.1 Mechanical joints. Mechanical joints on drainage
    pipes shall be made with an elastomeric seal conforming to
    ASTM C 1 173, ASTM D 3212 or CSA CANICSA-B602. Mechanical
    joints shall only be installed in underground systems
    unless otherwise approved. Joints shall be installed in accordance
    with the manufacturer's instructions.


    The most popular elastomeric seal would be made by Fernco and Fernco's stuff is approved for above ground installation.

    Some local code authorities and districts may well have ammended their code but overall, Fernco's are just fine. I do agree that the stack should be properly supported but then again, it should be whether there's PVC and Fernco's or not.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  7. #7
    Moderator & Master Plumber hj's Avatar
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    He is using the term "banded" improperly. No-hub and transition couplings ARE banded. The unapproved ones are the hoses with clamps on either end, commonly referred to as "ferncos". Here, "fernco" couplings can only be used underground OUTSIDE the building. Your condensate line would have to connect in the sink cabinet between the sink and the trap to eliminate the possibility of odors. Connecting it to the sink drain line would be exactly the same as what you have now.
    Licensed residential and commercial plumber

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    DIY Junior Member philwgreen's Avatar
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    So, it looks like I have two things to do. Connect the condensation line into the sink drain before the trap and replace those banded couplings.

    Thanks again for the help everyone.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    At least while you are replacing those "UNBANDED" couplings, (they are NOT "banded" ones), you can also eliminate "P" trap connection.
    Licensed residential and commercial plumber

  10. #10
    DIY Junior Member philwgreen's Avatar
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    Very true - just knock it all out at once.

    And yes, 'unbanded.' Looks like I forgot to type the 'un' in unbanded couplings in my last post.

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by philwgreen View Post
    Very true - just knock it all out at once.

    And yes, 'unbanded.' Looks like I forgot to type the 'un' in unbanded couplings in my last post.
    And, I got sloppy with the names as well, but the picture says it all...that type should not be used above ground!
    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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