Hot Topics: How Can You Tell if a Vent Pipe Is Working Properly?

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Original Post: How to tell if vent pipe is working properly?

GroundCurrent Member

If the vent pipes (that go out of the roof) are blocked or partially blocked, what would be the symptoms? Is there a way to test the vent pipes without climbing onto the roof? I'm concerned because there is nothing covering the pipe outlets (2-inch diameter, I think) and a lot of pine needles fall from fir trees around the house. Wouldn't the vent pipes get clogged by the pine needles eventually?

Norm201 Member

Yes! You should install a goose neck cap on it. I put a wire mesh over all my openings coming through the roof, but I have no trees to worry about, only the fear of birds or rodents getting in.

Bud9051 Member

Not a plumber, but as I understand it all the horizontal runs of any vent are sloped towards the departing drain line. For most of what might get in there (other than a larger critter) it should be washed down the drain by any rain. If you're concerned, when you go up there in warmer weather you could use a hose to wash anything down.

Overhanging trees are a problem in other ways such as cleaning gutters, roof debris, squirrels and, heaven forbid, a fire.

Vermont Member

Is there something about this home's drainage system that is clogged or not currently working, or is this just a curiosity issue?

core Member

Depending on the height of your roof, you could take a garden hose and carefully arc the stream of water so that it goes into the vent pipe in question. Have a helper open a clean-out in the basement/outside and watch for the water flow. Be sure to remind family members not to flush the toilets or this is liable to get messy.

Zorfdt Forum Topic Moderator

Another trick is to watch the water in a toilet bowl on a windy day. You'll probably see the water rise and fall a little with the gusts of wind over the vent pipe. As Bud mentioned, other than animals (or sometimes a squirrel using it for acorn storage) it's rare for vents to get clogged.

Paulypfunk Member

Vent clogs are very rare. If it does happen, I usually see it just upstream of where the drain connects to the vent. Schmutz sometimes collects and clogs it. Does the fixture bubble and burble when draining? If you remove the p-trap and drain a bunch of water into a bucket, does it behave the same? Can you sneak a snake upstream from the wall outlet? We might want more info from you to solve your problem.

GroundCurrent Member

I did this test and see no differences, so there is no issue with the vent. The problem I have is an odor coming from somewhere in the bathroom. I guess I have to look elsewhere. Thanks for the suggestions.

Paulypfunk Member

Smells are a tricky issue as they can have multiple causes. Does the sink drain normally when connected to the wall? Connect the trap, run water, get it back to normal, and then try this test.

If you can do it safely, go up on the roof and pour some extract of peppermint down the nearest vent. Then see if the room that you suspect has a leak smells like peppermint. If it does, you have a breach somewhere in the DWV system—a rusted pipe, a rat chewed a hole in something, a bad wax seal under the toilet. If there's no peppermint smell, the issue lies somewhere else.

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