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Is this correct?

I posted a picture below of a condensate P-trap and condensate drain. ... The coil is on the suction side of blower. ... is the trap piped correctly? And should there be a air vent after it like in plumbing? Thanks Paul Stessler
ASM Mechanical Company
Located in Staten Island NY
Servicing all 5 boroughs of NYC.
[email protected]


  • icesailoricesailor Member Posts: 7,265

    I looked at this again. The below seem to apply.However: Plumbers don't pipe those things so most plumbers wouldn't understand about the fan/drain issue.

    Maybe that's why you're asking about if the vent belongs between the drain and the P-Trap. That would break any syphon on the trap. As far as plumbing systems are concerned, it doesn't need a trap. The trap is in the indirect waste receptor where it enters the plumbing system.  

    I can't see anything wrong with that. From a plumbing standpoint, it is correct. Assuming that the drain opening (inlet) inside the unit is open, and the water can flow out without disruption, there is a P-Trap with a vent on the down stream side, between the trap weir and where drain ends. If there is any sort of internal trap inside the unit, the drain is now "double trapped" and won't drain. You would need the vertical vent pipe moved to

    Technically, it isn't plumbing until or unless the indirect waste from the appliance goes into the sanitary plumbing, into a properly wasted, trapped and vented indirect waste receptor with a air break.

    I don't have a code book, but I seem to remember that whatever the size of the drain leaving the appliance, the drain is supposed to be one pipe size larger. IE: If the drain tapping is 3/4" IPS, the drain needs to be 1". So there is more air flowing through the drain pipe. The inspectors I dealt with didn't care unless it was for an icemaker or some other device. If that drains out on the ground outside through a outside wall, they didn't much care.
  • TechmanTechman Member Posts: 2,144

    how do you clean out the trap on the yearly routine
  • icesailoricesailor Member Posts: 7,265
    edited April 2014
    How To:

    If you're asking me, I live in a 240 unit old carts place in Florida. They do things differently down here. Each and every unit has the AC unit inside and a 1" PVC drain run 25', under the concrete floor, that came out so low, that the "Trap" is upside down on the outside so the bugs can't crawl in (I guess). I had someone come and service the unit. I had them replaced the 1996 Ruud unit. The guy just came with his small Ridgid Home Depot shop vac, connected it outside and sucked the many gallons of water in the 25' trap, out. It was right nasty. I was told that a 25' length of 1" horizontal pipe with one end rising up 3 or more feet for a condensate drain, and an ellbow turning UP with another Ell turning Horizontally and another turning another turning down (an upside down P-Trap), on the other end, isn't a trap. It must be common because you can always tell when someone is comfortable with something you think is odd, it must not be to them. They want to extend the line away from the units after 30+ years. They bought 1" PVC running traps so the could have traps on the lines to keep insects from crawling in to the AC units up through the drain. I didn't score any points by pointing out that the only living creature that was going to crawl 25+ feet up that pipe was a fish. And that adding that running trap would make it double trapped. And not drain. Unless the head pressure of the water could overcome the trapped air between traps.

    Any of you out there ever inadvertently double trapped a plumbing fixture? It didn't drain, did it.

    So, if the question needs an answer, take the proper sized PVC cap and put it in that vent riser and suck away on the outside. It will work just like one of those Bouse House suck trucks that comes around and sucks up the honey from the job site Porta-Potty. Ma Nature hates a vacuum.

  • TechmanTechman Member Posts: 2,144
    edited April 2014

    How deep of a vac do you need to pull, in order to suck the mud out of the unit trap and up the riser? and then horizontal how far? In attic installed AC's, the main drain and the auxillary drain's lines usually have several bellys that retrap that used to be dust, now mud.
  • icesailoricesailor Member Posts: 7,265

    Usually, not a lot.

    In the above example, if you cap the vent riser, and connected the shop vac to the drain at the bottom, it will suck it out as easily as it does from the top. And you don't have the cart the vacuum to the top floor.

  • TechmanTechman Member Posts: 2,144
    edited April 2014

    From experience , the drain pan would have to be full, drain backed up, air break opening capped, shop vac running and that mud plug will be sucked thru as you said. Using an alarm trap is cool , putting a water proof pan in that hole would be nice, with a water alarm, and for a yearly flush out ,I would replace that 1st downward facing 90* ell with a T, an upward piece of 3/4 pvc( 2-3 in.) w/ a cap or plug;pour water down the 1st T ,flush that mud away, put cap back on. From new/cleaned ,a trap  can take 2-3-5 years before the trap plugs. Some customers "swear" the unit hasn't plugged in 20 years, and nobody has ever looked at the system, ever!
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