Do I need to glue/epoxy this PVC pipe on my furnace/AC?
December 30, 2021 7:55 AM   Subscribe

I just discovered some water on the floor of my basement, and it looks like a PVC pipe on my furnace/AC came loose. Pics here. I put the pipe back together and it feels pretty snug but should I glue, epoxy, or in some other way bond them together?
posted by Tehhund to Home & Garden (15 answers total)
Best answer: On my two air handlers, there are condensation drains with clean-out access caps which are not glued. Perhaps this section is not glued to serve as a clean-out access point?
posted by tomierna at 8:13 AM on December 30, 2021 [1 favorite]

Best answer: Ideally, you want to be able to unplug these pipes if they get gunked up (which could be the reason they came apart). Keeping this joint unglued may help make that more feasible in the future, but it depends on your set up. If you decide not to glue it, you might want to jam a piece of wood or something under there to support it.
posted by ssg at 8:15 AM on December 30, 2021 [2 favorites]

Run a piece of rope, bungee cord or a tiedown strap around the lower pipe where it disappears under the unit, then around the horizontal part of the pipe.
posted by Stoneshop at 8:26 AM on December 30, 2021 [1 favorite]

The specific connection shown separated in your pics probably isn’t the one it’s leaking from, since it would have to fill up everything below the top of that elbow first, and that shouldn’t happen. It could be leaking from the horizontal leg of the same elbow, or running down from a leak somewhere higher up. Besides tightening other unglued connections, I’d check that the path to the floor drain or condensate pump isn’t obstructed.
posted by jon1270 at 8:30 AM on December 30, 2021

tl;dr: This is a question that should be asked of whoever does your furnace maintenance, due to the potential risk of carbon monoxide poisoning if it's not handled properly.

My gas furnace has two PVC pipes attached to it, one of which is the air intake (to the combustion chamber) and the other of which is the exhaust. The fact that there's water would imply to me that it's the exhaust [methane (CH4) burns to carbon dioxide (CO2) and water (H2O), and some of the water condenses out as the exhaust gases cool]. The bottom leg of the pipe probably leads to a drain under your furnace. You can check whether the upper portion of the pipe leads to an opening in the wall and thus outside.

Any gap in the exhaust pipe that's not part of the furnace design could lead to exhaust fumes entering your basement, potentially killing the occupants of the house via carbon monoxide poisoning. This is something that I'd want a professional to check out. Also there may be other damage or exhaust blockage that caused the pipes to separate in the first place that you'd want to know about and have fixed.
posted by heatherlogan at 8:30 AM on December 30, 2021

heatherlogan: This is the condensate drain, which carries water to a drain in the floor, not the exhaust, so no need to worry about exhaust fumes.
posted by ssg at 8:53 AM on December 30, 2021 [3 favorites]

Response by poster: jon1270, I fiddled with the pipes before I took the picture. Before I fiddled with them they were much more separated so the top pipe could drip directly onto the floor without filling up the bottom. But you are right that I am not certain so I'm going to dry out the water and monitor the situation for a few days to see if more water ends up on the floor.

heatherlogan, ssg is right — this is for condensation. We have carbon monoxide detectors in every bedroom and a carbon monoxide detector in the same room as the furnace so if there were a carbon monoxide leak we would know. With that said we are due for maintenance soon so I will ask them to take a look.
posted by Tehhund at 9:02 AM on December 30, 2021 [2 favorites]

Non-professional here, but I believe code says there's supposed to be an air-gap there, so if the line backs up it overflows out the air gap and not back into the furnace. I think the top pipe is supposed to just be lined up with the bottom pipe so it drips directly into it, not tightly inserted.

Edit: although I can't see it because the top of the photo cuts it off -- is the "upper" pipe open to the air? That could be your air gap / cleanout, and then you would use PVC glue to glue the bottom part into the elbow (or just gently insert it, that pipe isn't under pressure and just 'guides' water out).
posted by AzraelBrown at 9:28 AM on December 30, 2021 [1 favorite]

Response by poster: AzraelBrown, the pipe is open at the top. But that opening is above where the pipe enters the furnace. So if water were backing up it would back up into the furnace. But I can't see inside that part of the furnace so maybe inside the furnace it opens higher up than the open top so it's okay to back up just a little bit into the furnace and it would spill out the top before it spills into the furnace. Anyway that's a good question next time we get it serviced.
posted by Tehhund at 10:13 AM on December 30, 2021

IaaArchitect, IanyArchitect.
The air gap needs to happen at the bottom end of that pipe where it terminates and goes into the floor drain. This keeps the pipe from sucking up dirty water if a vacuum should develop.
But since the water in this pipe is not for drinking/bathing/brushing teeth, and is not connected to any pipe that does carry that water, it's a bit less critical.
Condensate drains commonly just drip onto the ground with no trap, though a trap will help keep bugs from crawling up the pipe. Also gives crud a nice place to accumulate.
I'd be a bit surprised to find this as a "cleanout". Usually there is a vertical leg on the pipe close to the unit as Tomierna describes. The tech carries a compressed air bottle, and just blows the pipe clear if it gets plugged. This is a good PM thing to do about once a year. I have my HVAC guy come out once a year to check freon levels, blow the drain pipe, and just check for any issues.
You can also use a shop vac on the bottom end of the pipe to suck out any crud.
posted by rudd135 at 11:14 AM on December 30, 2021

If you wanted to be fancy, you could glue in a slip-join union, which will securely hold the pipes together but also allow for disassembly.
posted by jpeacock at 11:19 AM on December 30, 2021

Tehund, if that's the case it's exactly like my furnace's condensation pipe, and the PVC pipe is solid all the way to the floor drain where it discharges.
posted by AzraelBrown at 12:43 PM on December 30, 2021 [1 favorite]

Response by poster:
Condensate drains commonly just drip onto the ground with no trap, though a trap will help keep bugs from crawling up the pipe.
You can't see it in the pictures but this pipe ends on the floor drain in our basement. It just sits on the grate so it can't miss. I believe that drain has a trap. It's kind of convenient that this drains into that drain because in our last house we had problems with the basement floor drain trap drying out.
posted by Tehhund at 1:07 PM on December 30, 2021

Open at the top ---> definitely not the exhaust! You're safe. :)
posted by heatherlogan at 3:45 PM on December 30, 2021 [1 favorite]

Response by poster: Update: our furnace guy just did our annual inspection and said nothing is wrong with that pipe (and everything else looked good other than a small clog inside the furnace that has nothing to do with that particular pipe). I asked if it needs to be glued and he said he prefers if it's not glued so it's easier to open up and clean any clogs.
posted by Tehhund at 7:53 AM on January 24

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