How handle condensate drain trap in conditioned attic?
jameshowison
| Posted in General Questions on
Is there guidance for plumbing air-con condensate lines in conditioned attics?
The guidance here in the south includes an open “anti-syphon” stand pipe after the trap, then with that draining directly outside (new construction may drain into main plumbing). I attached a pic (from inspectors site).
But that creates an open pathway for air from outside to travel up the drain and into the conditioned space.
What are people doing for condensate in conditioned space that has its own drain to outside? Does any code or high performance building instructions give better guidance?
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Code will require an air gap after your trap and before the water enters the sanitary system and part of the air gap is a second trap keeping sewer gas out of the condition space.
https://www.carotek.com/userfiles/_images-pdfs-general/blog/Grundfos-HVAC-Commercial-Design-Guide-Summer2020.pdf
Walta
jameshowinson,
Use the detail they provide, but put an AAV on the air vent. All vents should either exit the building envelope (usually though the roof), or have an AAV.
@ Malcolm Taylor - I think your advice applies to sanitary drains. He is talking about a condensate drain.
User...022,
His worry is the drain being a source of air-infiltration, so the same solutions apply. Is there a situation where a plumbing vent of any sort should be open to the house? Maybe if it had a check-valve?
I agree with Akos though, the easiest way to eliminate the problem is to not drain directly to outdoors, however it seems from James' post that they require the drain to go outside.
The best possible system would have a drain pan under the AC unit with a separate emergency drain system draining to someplace you will notices like onto the sidewalk by the from door and a failsafe float switch that would shut down the AC should both drains get clogged before the pan overflowed.
A drain pan under the unit with a float switch costs much less that than drywall repair and repainting.
Note many local codes will require more than a primary drain.
Walta
Thanks Walta. All great points.
Yes, we have two float switches, one on the secondary (this is a mitsu multi-position airhandler on its side), and a separate one on the pan underneath. Either can shut the unit off.
See post below, these worked in the sense that we had a blockage in the trap and no water leakage or damage. Hurray.
But I did wake up at 4am very hot and try to figure out what was going on. Boo.
Didn't get it sorted until 10am when I stuck a $2 "hair remover" backwards through the vent and thus through the trap, releasing whatever the blockage was.
Got me thinking about how the condensate was figured. Three problems with mine:
1) no cleanout (just a "Jones" valve that was unusable for me)
2) trap was a dinky "bent 3/4" that creates an unnecessary constriction
3) trap not visually inspectable (blockage spot would have been obvious)
4) vent terminating in conditioned space and direct open pathway from there to the outside (through the drain), an unexpected air sealing issue.
Oh, and the Mitsu wireless thermostat doesn't really have an alarm. Just a really easy to miss alert in a triangle. Could it at least flash on and off so I can know if it isn't working? Audible alarm? Nope, just a subtle silent code (although at least this time "5701 float switch" was accurate and understandable :)
I think what you are looking for is this:
https://rectorseal.com/ez-trap-180-for-minisplits/
A better option is to drain to somewhere indoors, the tail stock of a bathroom sink, overflow of a tub or the riser for a washing machine are all great spots and much more accessible if they ever get clogged.
Thanks Akos.
This sent me in an interesting direction. These materials are from a vendor but interesting about traps drying out:
https://www.deschampstechnologies.com/ewExternalFiles/HVAC%20Air%20Trap-Whitepaper%20V2_0322.pdf
Apparently some movement on codes towards waterless traps, maybe primarily commercial?
https://waterless-trap.com/pages/hvac-condensate-trap-code-change
This seems like the one I would use (positive pressure, I don’t have 6” of drop available near the drain at the unit)
https://www.deschampstechnologies.com/products-mobile/plp-series-mobile-1.html#PLP-Mobile-Start
Anyway, but otherwise this is definitely a vent, so it should go outside conditioned space. I did think about an AAV.
Btw, thing that precipitated this for me was waking up to a hit house because the float switch in the secondary drain turned things off. Lots of water in the unit (not leaking into the pan) but I could look down this vent and see no water in the main drain.
There is a “Jones” valve cleanout but no other cleanout. The Jones valve is interesting, has a a header valve that you can send either way, but the fitting is for either CO2 or Nitrogen. No homeowner in the middle of the night friendly! Also doesn’t seem sensible to blast high pressure back towards the unit (and vent was between the Jones valve and the trap anyway).
$2 hair remover from Home Depot down the little vent and through the trap cleared it. HVAC guys not needed (can help so many others with failing units in this heat!)
But it got me thinking. Definitely these should have cleanout to go both ways through the trap, but why is the trap filling up anyway, and why is it not visually inspectable? Oh and now I’m thinking about this, won’t air pull from outside through from outside to this vent if the house is under negative pressure? What about bugs?
But as is often the case there is a better way and all y’all pointed me in great directions!
One alternative solution is to use a properly designed and installed mechanical trap seal, such as a check valve or a trap seal primer, which can prevent air from entering the conditioned space while allowing the condensate to drain efficiently. These options maintain the integrity of your conditioned space's air barrier.
Consulting local codes, high-performance building guidelines, and experienced HVAC professionals can provide you with the most suitable and code-compliant solution for your specific situation. Keep in mind that local climate conditions and regulations may influence the best approach.
Thanks. First paragraph is spot on.
Sadly, second paragraph doesn’t ring true, in my experience, because very little experience in doing units in conditioned space. They just do them like this and hope the water stays in the trap :)
That said, there is a float switch in the secondary drain port and in the pan under the unit. The secondary drain connection elbow for the float switch (SS2) is not glued, so air comes out of that. Which is no problem in conditioned space, but they do those in unconditioned space like that too.
Listen to Walta and post #4.
My house in FLA had one gravity drain in the attic above the garage. No emergency overflow drain. It got clogged one summer with mold while we were home in the Northeast. God knows how long the pan overflowed until we caught it. The sheetrock ceiling had collapsed by then causing a big, $11K mess. Thank God the insurance company covered it.
We put in an overflow drain as part of the repair.
It's a good idea to use a liquid level alarm on remote condensate pans too, so that you get a warning of pending overflow before disaster strikes. Make sure to use an alarm that is hard wired, so that a low battery doesn't defeat your safety system! Anytime you have a condensate pan in difficult to access location, a level alarm is a good idea to alert you to a potential problem that you wouldn't otherwise be aware of. This alarm is still a good idea with an emergency drain, since the emergency drain otherwise just buys you time -- it will eventually clog too, and then you're right back where you started with water problems.
Bill