S-trap on condesation line-Wrong?

**Donald Stauffer** · 07-07-2018, 10:15 AM

Discovered this on an Amana HVAC. I thought all drain pipes should be gravity descending. Is this wrong?

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**Jerry Peck** · 07-07-2018, 10:50 AM

S-traps are not permitted on any drain line.

A photo would help with what you were looking at (while it wouldn't change the above answer, it would clarify whether or not it was an s-trap).

**Jim Robinson** · 07-07-2018, 02:15 PM

Way better than what I usually see in my hood.

**Jerry Peck** · 07-07-2018, 03:10 PM

Were the photos there at first and I just missed them? Me bad (looking on my phone then, as I am now).

That not an "s-trap", that's a "running trap", and they aren't allowed either.

**Jerry Peck** · 07-07-2018, 03:19 PM

Originally Posted by BARRY ADAIR

the gas supply does not appear to have a proper sediment trap that i can see...maybe behind the elbow?
https://buyersask.com/wp-content/upl...ing-ok-101.gif

Looks like the appliance connector goes up, then makes a 'U'-turn down, to a tee, with the side of the tee going to the appliance, and the bottom of the tee is a short piece which collects any sediment.

Which is a proper sediment trap ... the bottom piece should be a 3" nipple (minimum) and looks like it might be 3"?

What is not shown is the radius of the 'U-turn' bend - too tight of a 'U'?

**Donald Stauffer** · 07-07-2018, 08:36 PM

Originally Posted by Jerry Peck

Were the photos there at first and I just missed them? Me bad (looking on my phone then, as I am now).

That not an "s-trap", that's a "running trap", and they aren't allowed either.

Thanks, Jerry. "Running trap", okay. I didn't know what to call it. Anyway, I'm going to note it. Appears to me that it could back up into the pan.

Don Stauffer

**Elizabeth Chambers** · 07-07-2018, 11:13 PM

Absolutely. Also, that gas piping looks a bit hinkey to me.

**Jerry Peck** · 07-08-2018, 07:06 AM

Don,

It's not that it will clog and back up, that could be a result of a trap actually doing something - a running trap does nothing (nothing that a trap is supposed to do) as water runs right through it ... no trap seal ... it's essentially just a dip in a run of pipe.

If that was a pipe with solid waste (sewer pipe), sure waste could collect in the dip and lead to blockage.

For an AHU, it let's air through, which could lead to condensate backup and/or condensate being sucked up into the air stream, etc.

I'm on my phone so I can't upload it now, put I've uploaded it before if you search for it - it's a Trane document on the proper trapping of AHUs.

**Gunnar Alquist** · 07-09-2018, 09:25 AM

Originally Posted by Jerry Peck

I'm on my phone so I can't upload it now, put I've uploaded it before if you search for it - it's a Trane document on the proper trapping of AHUs.

Attached might be the document Jerry mentioned. Certainly, it includes two diagrams of traps.

Regarding the one in your pic: I have seen that type myself and asked a plumbing/heating contractor about it. He stated that running traps have problems with large volumes of water (draining a sink or tub, for instance) and that since the A/C dribbles the water continuously during operation, the running trap worked just fine. However, California has low humidity, so the condensate drain does not flow as heavily as it would in areas with high humidity.

Of course, it is still a running trap and not allowed, and doesn't match either design in the included instructions.

Also, I should probably mention that I have never seen a residential A/C unit here where the coil was under negative pressure (before the blower). So far, they have all been positive pressure (after the blower).

One thing that I have never understood is why doesn't the secondary drain require a trap?

On an additional note, A different heating contractor mentioned to me that some coil boxes have built-in traps, and an external trap is not needed. Does anyone know how to tell the difference between the two? A lot of coil boxes around here do not have traps.

- - - Updated - - -

Originally Posted by Elizabeth Chambers

Absolutely. Also, that gas piping looks a bit hinkey to me.

"Hinkey"???

Watched "The Fugitive" recently?

**Jerry Peck** · 07-09-2018, 10:17 AM

I don't know what happened, but I thought I replied yesterday or the day before with the Trane document, but my reply is not here?

So ... I am posting ... attempting to post ... that Trane document once again - here goes:

**Gunnar Alquist** · 07-09-2018, 10:49 AM

Originally Posted by Jerry Peck

I don't know what happened, but I thought I replied yesterday or the day before with the Trane document, but my reply is not here?

So ... I am posting ... attempting to post ... that Trane document once again - here goes:

Ooo! I like that one!

**Jerry Peck** · 07-09-2018, 06:32 PM

That Trane document definitely helps in understanding AHU traps and why they need to be the way they need to be.

And, whenever you run into an obstinate HVAC contractor who insists that a trap is not needed, or that their funky trap is okay, all you need to do is sent them a copy of that Trane document and wait ... they have always (in my experience) never said a word, but, for some miraculous reason, the traps would be quietly and quickly changed out ... least the HVAC contractor be responsible for "water carry-over to ductwork, admission of potentially contaminated air, bacterial growth, potential water back-up and unit damage", etc, in the AHU and the ductwork ... oh, I forgot, and let a couple of those terms "slip out" when discussing it with the contractor, and that it takes a lot to clean up for those things, maybe even replacing the ductwork and the insulation inside the AHU ... just sayin' ... it helps the contractor with their comprehension when reading that document ...

**Gunnar Alquist** · 07-09-2018, 08:17 PM

Originally Posted by Jerry Peck

And, whenever you run into an obstinate HVAC contractor who insists that a trap is not needed, or that their funky trap is okay, all you need to do is sent them a copy of that Trane document and wait ...

I just visited HVAC-Talk.com and read a few threads on condensate drains. I found it amazing how many "professionals" did not understand trapping (much less know how to spell). It's sad.