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Trap or No Trap

During a discussion today, I was informed by another technician that condensate traps are not required on those systems with the drain on the discharge side of the indoor (evaporator) blower....

I was taught that condensate traps were necessary on any condensate drain to provide a liquid seal to enable proper drainage and to negate the venturi effect caused by the operation of unit's air flow.

They need to be sized properly to overcome any static pressure issue present in the system's duct work.

So....perhaps you could enlighten me and advise me of your take on the proper installation of condensate traps and why and wherefore.

I didn't feel like debating the issue with the other tech,but your opinion would help ease my own uncertainty..since I think condensate traps are needed regardless of blower air flow orientation.

Thank-you for your help.


  • don_205
    don_205 Member Posts: 66
    The tech

    The tech was right on the money.You only need a trap when you are installing a pulled thru coil.Aka,airhandler.

    Often time you will find that everything that travel with the air will end up in the trap creating clogged drain line issue.So everytime we see a trap on a discharge side of the unit like a furnace with a coil on them, they are removed.

    Your understanding of how the trap work is correct.its there to break a negative pressure.

    What trap do you guys used..P trap or running trap?
    Where do you feel is the best place to place the trap?
    And when do you know if the trap is deep enough?

  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    As Don mentioned, when the condensate drain is located on the negative pressure side, a trap is needed.

    What I tell technician is.... When in doubt, trap it!

    Installing a trap when the application does not call for it will not damage things, but not installing one when it is needed will....

    Hope this helps.

    The Professor
  • ddlong1286@yahoo.com
    [email protected] Member Posts: 139
    check your code!

    Check the Authority having Jurisdiction. Someone may make you install one on a positive coil because of the "code".

    Traps on the positive side coil just seem to cause problems!!

    Don in MO
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    Very true Don... Right or wrong, ya gotta follow 'em!
  • ddlong1286@yahoo.com
    [email protected] Member Posts: 139
    Gotta be Deep


    according to Carrier's new air handlers of a year or two ago they need to be deep!! I believe 4 inches. A running trap won't do and is a thing of the past. I noticed at a couple of wholesalers that the running trap isn't stocked or the bin is low and hasn't been reordered.

    I beleive everones's air handlers are going to need deeper traps or "real" traps to work right. Everyone is going to extremes to prevent air infiltration.

    I always liked the clear trap with the cleanouts and brush, can't remember their name thought.

    Don in MO
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    I always steer techs away from running traps. They always seemed like a short piece of PVC that got run over by a car to me...Hence I digress.

    At any rate, you are referring to the EZ-TRAP, which is a great product. The website is here:

  • don_201
    don_201 Member Posts: 19
    Hi Don

    You would be surpise of how many running trap I change out in my area during the summer.

    Many moons ago I work with a old man that would have us measure the static pressure across the system.And anything over .4 iwc he would have us add 2 inches to the depth of the traps.

    It was also of the times when all they carry were hogs hair
    filter material that he also had us install the trap outside the envelope with a cleanout T.We would then take the customer out and explain to them how to flush out the trap once a month.

    I was so lucky to start out in the trade with this guy as my teacher.He could be a butthead most days to work with and lots of time it was very diffcult to hold my tongue.
    I'm so glad I did.

    You are correct Don.When it come to trap one size does not fit all.

This discussion has been closed.