Trap and Vent – A Drain Debacle

This picture is from a recent call I ran that clearly had an interesting past. It had a condensate pump to pump the water just a few feet up to a drain that went to a common drain. The “cleanout” after the trap is supposed to be a vent, not a cleanout, which means it needs to be uncapped and vented higher than the indoor drain pan so that if the drain backs up, the water goes back into the system and trips the condensate switch.  We could not raise the vent with the current position because it would come right up in front of the filter.

My best guess is that when the installing contractor installed a new, larger air handler, it no longer had the fall they needed to get the existing drain, so they capped the vent (seen in the photo above before it goes into the wall).

I'm using this system as an example because it has every possible drain “don't” you could come up with:

  • No cleanout
  • No float switch (condensate switch) to prevent pan overflow
  • Vent improperly placed or causing filter obstruction
  • Using a pump when one wasn't originally needed
  • Using a common drain with no vent
  • No insulation on the condensate drain horizontal runs

We rectified as much of it as we could, which included:

  • Adding a condensate switch
  • Repiping with a proper cleanout and vent before the pump
  • Insulating the horizontal portions

Unfortunately, we couldn't eliminate the pump, and I forgot to take “after” photos.

This is an example of a drain properly pitched, insulated, trapped, and vented with a system and secondary pan switch installed. Two things I do notice on this one is that the pan doesn't look like it overlaps 3″ at the top of the unit, The cleanout would be better right above the trap, and I can't tell what's supporting this drain to ensure the pitch stays correct.

It's amazing how much there is to the simple, humble condensate drain.



4/1/20 at 09:56 PM

I never understood why FL does this. Up north we all just put a drain in the floor and drain it that way. Only one place in FL that I every went to drained it by going into the drain for the washer in the floor below.
It’s got to be the most annoying and problematic way to do condensate drains. And if you do any places in Baldwin park those are the worst – running drains from the 2nd floor down, then out back behind the garage, which has got to be over 100ft of drain.

4/4/20 at 09:54 PM

Drains being a substantial amount of my calls during the A/C season in the northeast, I do have to say that sticking to the old 3/4″ solid PVC traps is a pain when rectorseal makes a cleanable drain trap that can be installed just as easy (yes and one that comes with a float switch). Other than cost, is there a particular reason why people still choose not to use these types?

4/16/21 at 06:38 PM

So basically the vent in condensate lines is to help the water go down the drain line?

6/9/21 at 05:29 PM

Yes. When AC Coil precedes the Air Handler/blower, you have “negative” pressure (causing vacuum preventing water from draining); a P-trap negates that pressure differential allowing water to drain properly. All fittings of EZ-Trap allows easy cleaning, venting, and quick visual if trap has debris (also has a brush to clean ANY direction of the drain line).

7/30/22 at 09:10 PM

Florida like arizona has slab floors/foundations vs basement or crawlspace homes and the air handler is often in the attic. If you are lucky and its in a closet or the garage– and they thought to put a floor drain in when plumbing the underground before pouring the slab- then there are many options- I see so many ceilings ruined from overflowing pans —its just incredibly frustrating. I wish they would get rid of the gravity drains and require a real drain and or a pump- to avoid all these problems. during the summer the condensate flows regularly . In the winter- it evaporates and leaves hard water deposits. After a few summer/winter cycles- the 3/4″ pvc gets clogged up and the fun begins. Pan overflows, ceiling stained. I have seen installs where both drain pan and coil drain pipes as is pan, because both are blocked where they come out of the side of the house and take a 90 degree turn. Its an archaic system that when everything works—its great- but when it doesn’t, very extensive damage can occur.


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