What Is a Plumbing Vent Stack and How Does It Work?

C.E. Larusso
Written by C.E. Larusso
Updated January 12, 2022
A beautiful big white bathroom with black floor tiling
Photo: Woning Media / iStock / Getty Images Plus / Getty Images

Highlights

  • Your vent stack is an integral part of your DMV (drain-waste-vent) system

  • It provides air so water can flow easily through your home’s pipes, and releases gases from the sewer so they don’t get inside

  • Broken collars and clogging are two major issues to look out for, though issues with vent stacks are rare

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Your home’s plumbing system is a magical labyrinth, ushering in fresh water and removing waste when called on to do so. The nucleus of this brilliant feat of engineering is the plumbing vent stack, which supports all the pipes in the home, allows water to flow with ease, and prevents dangerous and unpleasant gases from getting inside. 

Read on to learn more about this feature and why it’s imperative to your plumbing system.

What Exactly Is a Plumbing Vent Stack? 

A plumbing vent stack is essential to keeping your plumbing’s drainage pipes working properly, and is the main component of your entire drain-waste-vent (DWV) system.

Your plumbing system is more than pipes below your sink. The plumbing vent—which usually extends 2 feet out of your roof, past any potential snow lines—controls the air pressure in your plumbing system. 

All plumbing systems require at least one vent stack. It is designed to vent all the gases that accumulate inside the system through the roof into the atmosphere, and helps maintain the trap seals of each fixture. In addition, the vent stack allows fresh air into your plumbing system that helps water to flow easily through the drain pipes.

How Does a Plumbing Vent Stack Work?

Your plumbing system’s drainage pipes, responsible for removing water and waste, empty into a sewer or septic tank. The vent pipes supply fresh air to the plumbing fixtures, which allows the system to push water through the drainage pipes every time you flush the toilet or run the sink to brush your teeth. 

In addition, the vents help your plumbing system release any sewer gases built up in the pipes. From time to time, gases flow back from the sewer system into your home, and this can carry an unpleasant plumbing odor that can make you and your family experience drowsiness, headaches, and nausea.

Types of Plumbing Vents

There are different types of plumbing vents, in addition to the stack. 

Here’s how they’re connected to create a well-functioning plumbing system.

  • True vent: This is the most common vent, and the kind we described earlier in the article. It is attached to the drain line and vents through the roof. No water runs through it.

  • Common vent: Let’s say you have two sinks on opposite sides of a wall. A common vent connects the two sinks via a sanitary cross, and links up to the true vent.

  • Revent or auxiliary vent: This one attaches to the drain line, near or behind the plumbing fixture and runs up and over to the main vent.

  • Loop vent: These are used for freestanding sinks not connected to walls, such as on a kitchen island. It forms a loop under the sink, drops under the floor, and then connects horizontally to the vent stack.

  • Air admittance valve (AAV): These open to let air in when waste drains out, with the pressure from gravity closing them to prevent gases from getting into the room. Some municipalities will allow AAVs to replace vent lines, and they can vent multiple fixtures to simplify your plumbing system. Check with your local building codes to see if AAVs are allowed.

Common Issues with Plumbing Vent Pipes

A plumber repairing a bathroom sink pipe
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Vent stack repairs are rarely necessary, but there are some common issues to look out for.

Broken Collars

The collar around the base of your vent stack, on your roof, is usually made of aluminum, with a rubber boot on the top of the collar. Over time, the rubber can deteriorate from harsh UV rays and other extreme weather. 

This can create a leak in your roof and allow water to get into your walls, causing water damage or mold. If you notice water pooling around the base of your vent stack, look into hiring a quality plumber. Or, if it has been a few years since you’ve had your entire system looked at, consider a full home plumbing inspection.

Clogging

A blockage in your vent stack can create a buildup of negative pressure in your drainage system, which means water won’t be able to flow out of your home well (if at all). You might have a blocked vent if you notice standing water in your sink or bathtub, extremely slow drainage, or hear gurgling sounds in your pipes. 

Hire a plumber to assess the situation. Items that might cause a vent clog include leaves, dead animals, and toys or other random objects that found their way to the roof.

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