Potentially frozen vent stack. Thoughts?

[NorthernGuy1]

So in the last few weeks I've noticed when I flush the toilet upstairs I can hear the tub drain behind me do a chugchug sound that it never did before. A few days later I started smelling sewer gas in the bathroom and had a minor worry my flange seal let go under the toilet, then I did the math. I poured some water into both the shower and tub drains in the same upstairs bathroom and the smell disappeared.

A few weeks go by and I noticed the chugchug is still happening and every few days I need to refill the traps. Again this never happened before. So my best guess is the vent stack is plugged with ice. We had a run of -40s about a month ago and then steady -20 to -30 days and nights. The issue started about the same time.

So thoughts on safely dealing with this? Temps will be below freezing until late May where i live. I've never had a frozen stack before and I can't see ice sticking out of it from my vantage looking from the road. My plan was to drop a bit of sea salt down and then a couple kettles of boiling water. I don't imagine it could hurt anything? It's ABS not clay or iron or anything weird.

Unsure what to do for prevention other than next spring go into the attic and pack/wrap the entire stack and connections in insulation?

 

[RS]

That's a pretty common problem in colder climates, I spent many winters in N Minnesota. A plumber told me about a solution once, but I don't remember what it was, maybe someone knows about it. We never has a sewer gas problem, usually it didn't stay froze very long.
You can just add some water to the traps frequently and sewer gas shouldn't leak. I wouldn't bother to go up on the roof, just pour the water into the traps where you have notices sewer gas. I suppose you could add an air admittance valve under one of the sinks, that should reduce the problem. If you google it there are pictures of how to install one.

 

[NorthernGuy1]

That's a pretty common problem in colder climates, I spent many winters in N Minnesota. A plumber told me about a solution once, but I don't remember what it was, maybe someone knows about it. We never has a sewer gas problem, usually it didn't stay froze very long.
You can just add some water to the traps frequently and sewer gas shouldn't leak. I wouldn't bother to go up on the roof, just pour the water into the traps where you have notices sewer gas. I suppose you could add an air admittance valve under one of the sinks, that should reduce the problem. If you google it there are pictures of how to install one.

I did add one downstairs after I first bought the house, mainly because tje downstairs sink was slow (trap was clear) but turned out to be a semi clog in the main. No plumbers here so i had to guess at the issue and my snake didn't reach a clog first go around. So I think that cheater is what is helping a bit right now.

I'm guessing that if the ice formed at a joint or bend in the stack it shouldn't split the abs as there would be air in front and air behind it letting it expand when/if it froze. Unlike say a pressurized water pipe with nowhere to expand to. So maybe it's not an emergency. Just very annoying.

 

[RS]

I have never heard of a vent stack breaking, it's just frosted solid and prevents airflow, it's not solid hard ice. Now, if you pour water down it and it doesn't melt through, then you might have solid ice. Wrapping the stack in the attic sounds like a good idea too. Our furnace intake and exhaust go out through the roof, and I have them wrapped with foam insulation in the winter, the intake frosted shut once and prevented the furnace from operating.

 

[havasu]

Our furnace intake and exhaust go out through the roof, and I have them wrapped with foam insulation in the winter, the intake frosted shut once and prevented the furnace from operating.

That could be very dangerous for occupants.

 

[RS]

That could be very dangerous for occupants.

No, not at all! The pipes are fully open on the end, just like they were originally. The insulation is only there to keep them warmer. And besides, the home is unoccupied in the winter months, but heated to 50F.

 

[havasu]

OK, I thought you were capping the intake/exhausts. Good to get this straightened out.

 

[NorthernGuy1]

So i went up on the roof today and had a look. There was a bit if ice lining the pipe, but the above roof section wasn't bad. I boiled a concentrated mix of water and salt and slowly poured it down the pipe. It never backed up like it was fully clogged or anything, the water went down decently and I could heard ice making tinking/crackling sounds as the water went down. Steam came up and kept coming up which at first may have been the water but after a while kept going and I figured i was just seeing humidity in the sewer gas making it through again. Went inside and flushed the toilet and no chugchug sound from the tub. Good to go it seems.

The fact it iced up inside the pipe either at the roof line or below just tells me I need to go in the attic after all this summer and insulate the pipe really well.