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4 min read

Everything About Plumbing Vents


4 min read

Everything About Plumbing Vents

RoofEverything About Plumbing Vents

The sheer size of a home's plumbing system can make plumbing issues seem rather complex. There are pipes in the basement, drains outside, bits of pipe coming out on the roof, valves, and elbow joints under the sinks...

So, how does one tackle the mysterious rotten smell, the slow-draining sink, the empty toilet tank, and the gurgling monster living in the pipes? Well, there's no need to get poetic about it; a damaged, improperly installed, or clogged plumbing vent could account for all of the above.

What’s a Plumbing Vent?

Also known as an air admittance valve (AAV) or drain-waste-vent system (DWV), a plumbing vent is an integral part of the drainage system that disposes of household wastewater. Specifically, it's the portion of the system that vents the pipes to ensure that the sewer fumes stay, well…in the sewer.

Plumbing vents ensure that there's a proper water flow without so much as creating a void in the p-trap (the part of the pipe under your sink that forms a U shape). When the p-trap lacks a minimum amount of water, noxious odours and fumes, including methane, are released.

Basically, a plumbing vent levels out the pressure in the pipes, forcing air behind the draining water, thus preventing gases from entering the home and keeping the pipes in good condition.

Normally, the drain pipes are routed through the walls, towards an exterior-leading vertical ventilation system. However, in some cases, this simple configuration is more difficult to achieve. Consider, for example, a sink embedded in a kitchen island. In such cases, small automatic discharge vents, which are commonly found in hardware stores and only used as a last resort, come into play. They're affixed directly to the drain pipe, opened while the air pressurizes the water, and closed when the flow is complete, keeping the trap well drained.

ceiling pipes_Everything About Plumbing Vents

Source: Flickr

Problems Related to a Faulty Vent 

Numerous issues can arise if:

  • The vent is incorrectly positioned;

  • The model installed is too small;

  • The exterior cap isn’t sealed properly;

  • Something is obstructing the vent (branches, leaves, nests, ice).

Keep an eye out for the early warning signs of such problems before the repercussions take over your home and completely clog your pipes.

  1. If you notice moisture build-up on your ceilings, check your vents before becoming overwhelmed by repair costs associated with a suspected cracked roof.

  2. If your home is developing a foul odour, then your plumbing vents may be clogged.

  3. If you notice that the water is draining slowly after bathing or washing dishes, it could be something more than hair or food scraps clogging the drain. If using drain cleaners fails to clear the clogged drain, consider inspecting your vents.

  4. If abnormal, gurgle-like or muffled noises are emanating from your pipes as water flows through, poor airflow might be to blame.

  5. A lack of air pressure caused by clogged vents affects the water level in the trap, therefore, when flushing, your toilet tank doesn't properly refill.

When in doubt, call in an expert.

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Automatic Drain Vent: Price & Installation

In most hardware stores, like Canac, Canadian Tire, Rona, and Réno-Dépôt, one can find the necessary tools and devices. Prices vary depending on size and use. A 1- to 2-inch ABS automatic drain vent meant to fit under a sink, if a conventional vent can't be used, costs between $4 and $20. On the other hand, an outdoor steel wall vent with a cap and gasket can run around $30.

wall vent_Everything About Plumbing Vents

Source: Flickr

Hire an expert to install an exterior or a roof-mounted vent. Assuming that you need to change the vent below the sinks or the ones accessed during renovations, here’s a run-down of all the materials required and the steps to follow. 


  • Vent;

  • A container/bucket to collect water;

  • A pipe cutter or metal saw, depending on the plumbing system’s materials;

  • Locking pliers;

  • Measuring tape;

  • Cement and sealant tape (silicon or Teflon);

  • PVC primer;

  • Joints, traps, and pipes to complete the work depending on the extent of the project.

First off, place a bucket or container under the sink to avoid creating a mess, unscrew the nuts and bolts holding the drain trap in place, and remove the elbow joint. 

Get a hold of a sanitary tee (T) and pipes. Depending on the configuration of your installation, you may have to trim the pipe a bit. Note that the bottom part of the vent should be about 4 inches from the top of the trap (maximum 30 inches), so measure your pipe extension accordingly.

Connect all the components without glueing them to make sure everything fits as it should, and if necessary, make any adjustments. When everything looks as it should, with a marker, label where everything lines up (pipes with joints).

Take the pieces apart, apply the glue, then hook up the pieces before linking the whole thing to the existing piping under the sink.

Install the vent at the top of the vertical pipe as per the manufacturer's instructions and apply sealant tape before screwing on the nuts and bolts.

Next, secure the trap by sliding the elbow joint onto the drain fitting and inserting the pipe arm into the T-joint. Screw on all the nuts.

Lastly, test it out by filling up the sink with water and removing the stopper to see if there are any leaks in the wastewater flow.

vent under sink_Everything About Plumbing Vents

Source: Sketch made in Paint 

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Last modified 2023-11-07

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