What is a Plumbing Vent?

Mary McMahon
Mary McMahon

A plumbing vent is an area of a plumbing system which vents air from the system. Plumbing vents are an important part of a structure's plumbing, and they are required by building code in many regions of the world. An alternative to the traditional plumbing vent is an air admittance valve (AAV), which is allowed under building codes in many areas. People who are not sure about what is required or allowed can consult the building inspector in their region; it is advisable to do this before starting a new project to confirm that the project will adhere to the building code from the start.


Plumbing vents consist of pipe lines which connect to the plumbing to carry air away from the system. Commonly, multiple venting pipes join together and connect to a single pipe which pierces the roof or runs up the side of a structure to release the vented air. The width of the pipe can vary, and the top is usually covered with mesh or a cap to prevent things from falling into the plumbing vent.

The vent serves a number of important functions. One function is to maintain neutral pressure in the plumbing. This facilitates the flow of fluids through the pipes, reducing the risk that fluids will stop flowing or bubble back into fixtures such as sinks and toilets. When plumbing vents become clogged, people may notice that drainage takes a long time or that bubbles appear in the toilet. Another function of the plumbing vent is to safely vent gases into the atmosphere, rather than allowing them to build up.

When a plumbing system is laid out, the plumber who designs it determines where vents need to be placed and how they can be most efficiently organized. Venting often requires going through the roof, which requires coordination with roofing crews. If AAVs are being installed, it is not necessary to lay pipe through the roof, which can cut down on costs in addition to creating a neater aesthetic appearance by keeping the roofline free of plumbing vent pipes.

It is important to keep plumbing vents clear. If people experience problems such as slow drainage and bubbling, they may want to inspect the vents attached to the line for obvious signs of clogs. They should also make sure that the gratings and screens which cover the vents are kept clear so that air can freely escape.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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