This is what your plumbing vent pipe does and how to identify a problem with it

I’ve been a master plumber since 1981 and, as crazy as this sounds, I love installing plumbing pipes of all types, including traditional black-iron piping for gas lines. It’s my hope that one day you get to spin a cutting die around the end of an iron pipe to create threads. When you experience the deep satisfaction of seeing spiral threads produced on a pipe that was smooth just minutes before, you might understand why I gravitated to this profession.

Steve discovered that I do over-the-phone plumbing coaching. Just six months ago, Zoe in New Mexico got me on the phone twice to help her install the plumbing drain and vent pipes in a house she was building herself. A month before I had drawn the necessary plumbing plans, she needed to obtain her permit. It made me so happy when she let me know her inspection passed with flying colors. Good for you, Zoe!

Years ago, the plumber who installed Steve’s platform tub took a logical shortcut and installed the required vent pipe for the tub drain line on top of the subfloor. There was plenty of space to do this under the platform, and it met the code requirements.

It’s important for you to understand the importance of plumbing vent pipes. They are the pathway air must follow when you decide to flush a toilet, use a washing machine or brush your teeth.

Before you turn on a faucet, the only water in the plumbing pipes in your home is sitting still in a p-trap under a fixture or floor drain. This water in the p-trap provides a barrier that prevents vermin and sewer gas from entering your home. When no water is flowing, both the drain pipes and the vent pipes are simply filled with either air or a mixture of air and sewer gas.

As soon as you flush a toilet or run water in a fixture, you introduce water into the drain pipes. This water displaces the air and sometimes pushes it down the drain pipes like a snowplow pushes snow. The air must be replaced immediately — and this happens by air being sucked down into the pipe that sticks up out of your roof. All this time you thought that pipe worked like a smokestack just letting gas out, didn’t you?

If enough water travels fast enough through the plumbing drains and the vent pipes are clogged or nonexistent, a vacuum will form and the needed air will enter the system via one of the plumbing p-traps.

Perhaps at some point in your life, you may have heard a slurping noise from a tub or sink when you flushed a nearby toilet or a washing machine started to pump water into the system. This gurgling or slurping noise is air making its way into the system. This is not a good thing, as the p-traps then lose their ability to stop sewer gas and vermin from entering your home. You want vent pipes to be installed correctly and to be free of debris. There must always be an open pathway up from each fixture to the roof.

Steve supplied me with excellent photos of his situation, so I understood how to solve his problem. I described how he could relocate the vent pipe so it was no longer above the floor and yet would meet code and function properly for decades using Mother Nature’s tool set.

I really prefer venting plumbing fixtures with pipes that interconnect with one another and eventually exit the roof of a house. I recorded a video showing this in the last house I plumbed for a friend. You can see it at AsktheBuilder.com.

You can have multiple vent pipes poking up through the roof to save on pipe material. It’s so very easy to flash the vent pipes so you never have a roof leak. I prefer to use a flashing boot made by Lifetime Tool that has a powder-coated metal base and a special silicon-rubber boot that’s far better than the flimsy plain rubber boot flashings used by most plumbers.

Every few years, assuming you can get up on your roof safely, you should put a garden hose down the roof vent pipe and run water down the pipe for a few minutes to wash out any accumulated dust, tree debris, or even bird poop.

If you do this, be sure you put sentries within the house to spot any leaks. Although it’s very rare, it’s possible a vent pipe in an attic or in a wall might have a crack or a fitting was never properly sealed. This might not be a problem for air, but it becomes a big issue when you’re putting gallons of water into the vent pipes!

You need to have someone by the hose faucet handle who can turn off the water immediately if a leak is spotted. You’ll benefit from discovering this leak as it could be the reason you’re noticing a slight sewer gas smell every now and then!

https://www.washingtonpost.com/business/2022/02/22/this-is-what-your-plumbing-vent-pipe-does-how-identify-problem-with-it/