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Central Air Conditioning drain…

JDLee | Posted in Energy, Heating & Insulation on December 21, 2007 10:47am

My furnace (and a/c coil) is in the attic of my single-story home in San Diego.

The condensate drain is 3/4″ PVC with a “P” trap piece.  It is connected a few feet away to the ABS vent pipe from one of my bathroom drains (a tub/shower drain).  There is no seal or fitting where the PVC connects to the ABS; the installer just drilled a hole that is just big enough to insert the 3/4″ PVC into.

Is this the proper way of draining the water from the coil?  Should there be some fitting to connect the PVC to the ABS vent more securely?

I have my walls open now, so I’m able to do this whatever way is best.

Thanks for any info/advice!

…

 

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Replies

  1. User avater
    CapnMac | Dec 22, 2007 01:16am | #1

    Peachy, ain't it?

    That's called "wet venting."  It's mandated practice, here in my town.  A-coil drain must connect to sanitary system through the nearest stack vent.  The condensate drip pan under the A-coil must be drained to daylight.

    (This is fun, too--not so much yellowjackets in the attic, as mud daubers plugging the drain line; or, after the a/c unit gets old enough, raising colonies of mosquitos in the attic . . . )

    If you want to (and your AHJ allows) you can get a better fitting to make up the wet vent.  Just double-check to see if you are required to leave it accessible for service (mine have to be in plain sight).

    Occupational hazard of my occupation not being around (sorry Bubba)
    1. JDLee | Dec 22, 2007 02:54am | #2

      Hi CapnMac,

      Thanks for the answer.  I don't think I know enough to follow what you're saying, though.  You said:

      "A-coil drain must connect to sanitary system through the nearest stack vent.  The condensate drip pan under the A-coil must be drained to daylight."

      What's the difference between the two things you mention?  I mean, you say one must be connect to the sanitary system, but the other must drain to daylight. 

      Are you saying mine is right?  What is it that I need to have draining to daylight?

      Thanks,Lee

      (also, what is an "AHJ?")

      1. User avater
        CapnMac | Dec 22, 2007 04:03am | #4

        A/C coil is supposed to have a drain inside the box with the coild, to catch the condensed moisture as warm humid air passes over it.  Then, most a/c units have a pan drain under that box with the coil in it.  That's because, in a ventialted attic or crawlspace, the box can get cold enough to condense water vapor out of that air onto the coil box.  The drip pan catches that condensation.

        You have to have some way to cope with both kinds of water once they collect.

        For me, the AHJ (Authority Having Jurisdiction) would be the Planing & Development Department of the City of Bryan, Texas.  Under their rules, the A-coil (internal) drain is routed to the nearest stack, where it drains into the sanitary sewer system.  The pan drian, drains to daylight--in my case, by was of some ABS piping poked through a gable wall.

        As a matter of design, I'd prefer to let the coil drain to daylight rather than add water to the sanitary sewer system to be treated (which is middling dumb, as it's practically distilled, from the condensation process).  Mostly, I think it's bad muni code as it "teaches" the havac guys to drin to a stack, and out in the county, on a septic system, where it's not ideal practice at all.  Having an ope catch pan, with an open line to the outside of the house is also on my list, we have plenty of habitat to raise mosquitos in as is (and not every one does as I have and pokes glass wool into the pan drain outlet).

        Is your's correct?  I don't know.  I mayhave one more drain than you are seeing.  It might not (I've seen catchpans with e plastic plug still in the drain mouinting hole).  You can generally get on the website of your AHJ and find out, though.Occupational hazard of my occupation not being around (sorry Bubba)

        1. JDLee | Dec 22, 2007 04:29am | #6

          Thanks for all the responses.

          Maybe things are different here in San Diego.  My coil is inside a box.  The box is a sealed, well-insulated, so if you touch the outside of it, it is always about the same temperature as the surrounding attic.  It never feels cold to the touch.

          The box has two drains.  One is the main drain (the one I'm talking about), the other is the emergency drain.  The emergency drain must be a bit higher or something, because it only drains if the main drain backs up.  The emergency drain terminates in an obvious place so that if you see water coming out of it, you know the main drain is backed up and must be cleared.

          I agree with the advisability of a P trap.  I may add one to the ABS where the A/C drain will enter.  It's a single-story home, and the ABS vent goes straight down and connects directly to the shower drain pipe (just ahead of the actual shower "P" trap and drain).

          1. User avater
            BillHartmann | Dec 22, 2007 07:41am | #7

            You all ready said that you had a P trap on the drain.Don't need or want another one.The setup is fine, just not done correctly.There are saddle T's. I don't think that they meet code or maybe it is just not approved for for all jurisdictions.Now here is one that type. These are too big for your application, but I think that there are smaller ones.http://www.missionrubber.com/Products/TFlexSewer.phpAnd there are these type. But you can't solvent weld PVC to ABS, so they won't work.Your other choice would be to cut the vent and put in a T. If you use an ABS T then you will need a rubber coupling to the PVC. Or a PVC T and 2 rubber coupling back to the ABS.This main condensate drain is from the internal pan under the evaporator coil.There is a separate pan under the whole unit . It is designed to catch any water if the coil pan drain becomes clogged.Often a float switch is up in the overflow pan so that if it's drain is also clogged then it shut off the AC before water comes through the ceiling..
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          2. User avater
            BillHartmann | Dec 22, 2007 07:48am | #8

            I could not find the saddle t that I was thingking about.But here are 2 all rubber T's that would work and solve the ABS PVC problem in one step.http://fernco.buyplumbing.net/store.php?category=620112
            http://www.missionrubber.com/Products/HomePlumbProducts.php
            .
            .
            A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          3. DanH | Dec 22, 2007 08:57pm | #11

            Your "emergency drain" is the "drain pan" described elsewhere. Often it's just a metal pan below the air handler box.
            If your view never changes you're following the wrong leader

  2. MSA1 | Dec 22, 2007 04:00am | #3

    I dont have anything to back this up with except logic. It would seems to me that an unsealed opening into you DWV in your attic would allow sewer gases into your attic (and potentially into your HVAC ductwork). I would think it should be either a sealed connection or at least a p-trap.

  3. User avater
    popawheelie | Dec 22, 2007 04:18am | #5

    I like to have mine go to a P trap. But I don't have the line glued into the P trap. Just have it inserted into the top of a pipe that goes down to the P trap. Like the hose that comes out of your washing machine.

    I'm not a plumber and don't know code. A P trap is good to keep sewer gasses in the sewer. And sometimes your line from the air conditioner will clog up so you need to be able to pull it out and clean the whole line. So having it not glued into the P trap alows you to do that.

    1. DanH | Dec 22, 2007 08:54pm | #10

      The problem with a P trap is there's nothing to keep it wet in the off-season.
      If your view never changes you're following the wrong leader

      1. User avater
        popawheelie | Dec 22, 2007 10:22pm | #12

        That's true. I'm not sure what the answer is to that. Pull the condensation tube out and plug it in the off season?

        1. User avater
          BillHartmann | Dec 22, 2007 10:29pm | #13

          In most cases in a colder climate there would also be a furance.And if it is a modern high eff gas or oil furnace then it will produce conbustion condensate that will keep the trap filed..
          .
          A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.

          1. User avater
            popawheelie | Dec 22, 2007 10:34pm | #14

            Now why didn't I think of that. I have a high eff furnace that drains into and little lift pump. I've heard it pumping several time this winter. You'd think I'd remeber that if I've triped over it several times.

          2. JDLee | Dec 23, 2007 05:19am | #15

            I appreciate all the input.  It's great to be able to get info from several sources.

            I guess we do kind of run A/C all year here.  We haven't had a need for it since late October/early November.  And we might not for another month or two, I suppose.  But I always run my air conditioners, in my house or cars, at least once a month.  I was told that doing so helps prevent the seals from shrinking.

            Jeff--You are right about things being much different here.  I watch a lot of home improvement shows, and I'm always surprised by how different things are elsewhere. 

            I never see vapor barriers here.  A friend of mine bought a house in 2003 that was at least 80 years old, and it did not have and had never had any insulation.  None in the attic, none in the walls.  That did make the house noticeably less comfortable, but it was obviously livable.  There's also no concern about frost, snow, frozen pipes, etc.

            Most houses don't have rain gutters.  It can easily go months and sometimes years without any appreciable rainfall.  In fact, rain is often so rare that you're tempted to just stop working when it occurs.

            I recently replaced the siding and windows on a 20 year-old addition to my house.  There was felt under the cedar lap siding, but no flashing or caulking around the windows, much less any sort of drain pans.  And after 20 years there was virtually no evidence of water incursion.  I wanted to do significantly more weatherproofing when I installed the new windows, but I couldn't find anyone who sold or knew anything about window drain pans.

            The foremost building concerns here are earthquakes, and, more recently, fires.

          3. User avater
            popawheelie | Dec 23, 2007 06:34am | #16

            Are you in So Cal? I grew up there. I understand about different building practices. Still energy prices aren't what they used to be and wiil continue to rise. Also people expect houses to be tighter and more energy efficient these days.

          4. JDLee | Dec 23, 2007 07:50am | #17

            Yes, San Diego.  And newer houses are, of course, built with insulation.  It's just that this is one of the few places that you could live relatively comfortably without insulation.

          5. User avater
            popawheelie | Dec 23, 2007 08:09am | #18

            I know. I've found that I'm primarily building for two people. Myself and the future owner. I know what I want but have to settle for what I can afford. But I'm also building for the next owner. I have to think, what would they expect?

  4. JeffinPA | Dec 22, 2007 08:23pm | #9

    Interesting.  I guess AC runs all year out there?  If we were to do that in the northeast, the 3/4" trap would dry out in winter (no water unless there is a condensing furnace) and sewer gasses would get into the house.  To hell with jurisdiction, sometimes I have to tell clients that is what the law requires, but to have to smell toxic and noxious fumes is out of bounds. 

    I recon you are in a different world out there, but regardless, I would want a tight seal on the connection to the sewer vent and completely sealed to the trap.

    BTW, the drain pan that is under the unit that CapnMac mentions is great when the 3/4" trap clogs and the system overflows.  Saves you from the drywall repairs.

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