Frozen Vent Problem

[FMC1959]

I live in the great white north, plenty of snow and cold weather. I bought my house new construction 10 years ago and last year during a very cold spell had sewer smell in the house. When temperature got milder, smell went away.

First cold snap this year and same issue. The smell is coming from upstairs bathroom. Main floor has kitchen, second bathroom, garage drain and basement drains, none of these ever smell. When I flush upstairs toilet during these cold spells, I hear the distinct gurgling sound right after the flush, like the water being siphoned, and this sound goes away with milder weather. Quite convinced this vent is freezing up.

I checked attic last year and there are at least 2 vent pipes that go out to the roof. Because of where upstairs bathroom is located, quite sure it does not share venting with other plumbing. Attic is very big, 20 x 28 and very high pitch roof, 20 foot apex in the attic, very well ventilated.

Two options I am considering for my problem. First thought is the vent pipes run close together before exiting the roof, putting a “T” on each pipe and connecting them together, allowing the upstairs bathroom to use the other vent when it freezes, or using its own when thawed.

Option 2 is to put an AAV on the vent pipe for the upstairs bathroom, installed in the attic. Would either solution be against code, but more importantly, would either solution pose health hazards, or other plumbing issues?

In the summer I could see about having a larger diameter vent pipe, that hopefully would not freeze, put through the roof. Not an option I would like in the middle of our winters and with the high pitch roof I have.

Thanks

 

[Caduceus]

I can't imagine that a vent would freeze unless something dramatic has changed in the past ten years that you haven't noticed. A sudden change in performance of the drainage/vent system usually indicates that there is a clog in the drain and the vent stacks are not the problem.
I have seen ice clogs in drains from slowly leaking toilets with water trickling down the drain when not properly insulated. Typically a flush will clear the drain in a few seconds before getting to the sewer beneath the house and not have time to freeze. A slow flow of water could build up over days and bottleneck the drain causing a loss of trap seal and sewer odor as well as the gurgling that you described.
Quite the theory, eh?
It happens here in Pittsburgh when we get deep freezes that last a week (20 deg. F. or below).

 

[IFIXH20]

If the vent pipe has lead flashing I would also check to make sure the lead is folded proprely over the vent pipe

 

[bgreen]

On very cold days flushing the upstairs toilet causes a gurgling sound from the adjacent sink and bathtub. I think this is air being drawn into the sink and tub traps because the vent pipe is blocked somehow. In my attic all of the house vents are joined to one vent pipe going outside through the roof. These are large vent pipes with no low points where water could collect and freeze so I can't imagine what is blocking the vent.

When the weather improves I plan to go up onto the roof and look down into the vent pipe to look for anything obvious blocking it.

Any ideas or suggestions are appreciated.

Bob

 

[Caduceus]

Most problems like you have described are caused by clogs, not venting issues.
If this is happening on cold days, specifically below freezing, look into the above post a s a cause of the problem.
Check for leaking faucets or toilets that are on the same part of the drain that leak water from the tank to the bowl and cause a minor ice dam in the piping.
First choice for me would be to suspect a clog.

 

[bgreen]

Thank you for looking at my problem. The clog makes sense but perhaps you can help me understand why the sink and tub gurgle. If the drain pipe is clogged with ice, the toilet water would backup behind it and drain through slower than normal. There would be no vacuum behind the water to suck air through the sink and tub traps.

Since air is being sucked through the sink and tub traps, there must be a vacuum in the vent pipe somewhere above the toilet water.

 

[phishfood]

Caduceus is probably speaking from the perspective of someone who has chased supposed vent problems, only to find that it was a clogged drain, not a vent, that was causing the problem. I know I have, multiple times.

What is likely happening is that the horizontal drain pipe is filled with water, but there is air trapped between the main drain pipe and the traps of the sink and bathtub. When the toilet adds more water to the line, the air is put under pressure, and bubbles up through the traps.

Don't get me wrong, a clogged vent can cause problems, and your problem COULD be caused by that. But in my experience, that is very rare.

 

[Caduceus]

As Phish said, very rare for it to be a vent issue. When you have traps getting 'sucked' and imagine a vacuum as the cause, the real situation is that the trap seal is actually getting pushed from atmospheric pressure from the room, not inside the vent pipes. So no vacuum is involved. Without diagrams to explain it all it's kinda hard, but try this to see if it's a clog. Fill up a 5 gallon bucket of water. Start running a steady amount of water in the sink for about 5 minutes watching that it doesn't overflow and flush the toilet a few times, maybe three. On the fourth flush, with water still running in the sink dump the whole 5 gallon bucket full of water steadily into the toilet. This is to fill the drains with as much water as possible at once.
With most partial blockages, if you put enough water into the pipes you will see water come up at the lowest point....the tub. That's what we are looking for to confirm a block in the pipe. Water rising out of the tub drain.
In some cases this works to confirm a clog, sometimes it doesn't.
Also, with a single main vent, if the vent was clogged you would typically see problems with trap seals on lower floors as well.