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Condensate drain trap question:

I had my AC replaced today. A very fine job. This has nothing to do with the installation.

I own in a over 55 development built in 1982 with 240 one floor units. The condenser is in the middle of the house in a closet and the drain runs 20' under the floor to the outside. When we bought the place in 2005, I noticed that there were two condensate drains coming from under the slab to the outside but only one ever shows condensate. I never thought much about it until today when the installer was talking about the drain backing up and the safety switch that would shut down the unit. Old system blows the water out, the new one does something else. Blah Blah. Being a Licensed Master plumber and having a keen understanding of traps and their function, it occurred to me that the traps were inverted and the trap dip was above the outlet. I asked the installer about it and he was clueless as to what I was talking about. I told him that if the horizontal 1" PVC pipe was pitched under the floor slab and drained to the outside, that is the ell on the end faced UP, with two other closely spaced ells like a plumbing trap, the whole line under the floor became part of the trap and would fill with water. He said it wouldn't. Every unit (all 240 of them) are drained like this. There are a lot of funny things in Florida but what the? He said that the line would drain, that it wouldn't fill up with water. Last Summer when I had it serviced, he sucked a large amount of nasty water out of the drain outside.

Any explanations?


  • TechmanTechman Member Posts: 2,144
    drain trap

    The drain line exits the AirHandler horizontally then ,1- an ell goes down (6") into the trap,then thru the trap , then back up for 1/2(3") the length of the drop. Then the drain goes down hill after that .At this point we put in an open "T" for drainage, air out water in. Also, on the horizontal of the trap we put in a "clean-out T" , unscrew the pipe plug and clean out the trap. or 2- horizontal out of the AH, then a " T" with the  "run "of the "T" being vertical. The bottom "run" goes down into the trap and the top part of the run goes up. That top "run" must be sealed or capped. After the trap all that water in the drain line just drains away, and junk/gunk/crap does accumulate in the drain line.

  • SpenceSpence Member Posts: 316
    Condensate Lines

    Is it possible you have an ill-conceived secondary drain? Code requires an independent one, yet I have seen many incorrectly tapped off the primary. Also, could the other line be your neighbor's drain?
  • RJRJ Member Posts: 483

    Over the years I have seen hundreds of poorly installed and misunderstood cond. trap installs    If the condensate pan is on the inlet side of the fan then a trap is needed or the static of the fan will not allow water to drain.  Can you post a drawing of your system.  the dimensions of the trap, especially in larger units depends on the air static of the system
  • icesailoricesailor Member Posts: 7,265
    Condensate drain:

    Someone mistook my camera and case for a Fanny Pack and decided they wanted it. I have no camera now.

    There isn't any problem with it draining. And how it is connected inside is proper. Its OUTSIDE that is the question. Every unit is piped the same way, all 240 of them. Each unit has two drains, one isn't used. It must be OK because after 30 years, there should be problems somewhere. I don't seem to have a problem and maybe it is the CAP (Commonly Accepted Practice) here. From a plumbing standpoint, a trap belongs below the drain, not flipped over and above the drain.

    You can make a "P" Trap with three ells. Two ells connected together on the same plane. The third ell, connected to a horizontal pipe and facing down. Connecting the two ells to the downward facing ells, allows the water to make the trap. The liquid level is determined by the overflow level of the last ell outlet. If you put a 12" piece of pipe, the water in the drain has to get high enough to overflow the 12" piece. The whole length of the drain will be full to a level line, 12" above the overflow. Turn the whole assembly over 180 degrees with the 12" pipe facing down, and the level in the inside pipe becomes the lever needed to rise above the inside of the two ells.

    Its not how plumbers are taught to connect or run indirect wastes.
  • unclejohnunclejohn Member Posts: 902
    Must be

    To keep critters and the like out because you are right. They would have to hold there breath for 20 feet before the could gain entry to your house because the line as you described it is full of water.
  • TechmanTechman Member Posts: 2,144

    I agree unclejohn, that has to be some nasty water!
  • icesailoricesailor Member Posts: 7,265
    Florida thing?

    Maybe its a Florida thing. They do a lot of different things down here.

    I'll have to look and ask around. Maybe this is a different place in the world where things are different.
  • icesailoricesailor Member Posts: 7,265
    Indirect waste drains:

    What I was taught and tested on is that indirect waste drains are supposed to have a free flow of air throughout the drain from the outlet to the inlet. And that where it connects from the source, there has to be a air break at both ends.
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