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What Are Plumbing Vents & Why Do You Need Them?

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We all depend highly on our plumbing systems working to avoid disruptions to everyday life.

If you don’t know what a plumbing vent is or why you need one in your home, this post is for you. Plumbing vents are an integral part of any plumbing system.

What Are Plumbing Vents & Why Do You Need Them? Photo

They allow fresh air in as well as letting smells and sewer gasses out of your plumbing. This stops your home from smelling bad due to everything flowing through your pipes. With a vent, these smells have a place to escape.

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What is A Plumbing Vent?

Plumbing vents are also referred to as vent stacks. They help to regulate the air pressure in any plumbing system. In addition to allowing sewer gases to escape, they provide an entry point for fresh and clean air into your system.

Having fresh air in a plumbing system helps water flow easily through the pipes. However, a plumbing vent does not deal with water even though it is part of a plumbing system.

It is a vertical pipe that generally goes through the roof of your home. This is where it provides an entry point for air and an exit for odours and gas.


P-Traps are a modern invention that has helped manage fumes in plumbing systems. They are the curved part of the pipe appearing in the majority of drains nowadays. This curve helps fumes go through the plumbing and leech back into the house.

Previously, trapped water was released when the water went down the drain. Having an additional pipe in the system gives air into the drain which prevents this inefficiency.

Vent Pipe System Specifications

The vent stack refers to the main pipe which leads to outside on your roof. It is the main way gasses get through your plumbing and up out to outside. This helps maintain the optimal atmosphere inside your system for it to function effectively.

The vent stack should lead from the main bathroom to the outside and extend between 1 – 2 feet above your home.

The diameter of this vent pipe should not be smaller than 2.5 inches if it feeds to at least two drainage fixtures. Generally, in a home for a small family, the pipe needs to be at least 3 – 4 inches to serve the whole home effectively.

The vent stack is the main vent and other attached vents can be smaller. This is much in the same way that you have a tree trunk and then branches coming off it.

For the smaller vents to reach the fixtures they serve, they can be installed horizontally. However, many are sloped as this helps airflow work better in the system. Plumbing codes usually define how sloped these must be.

Many plumbing codes will also define where a vent should connect to a fixture. A common example would be more than 6 inches above flood level for the fixture.

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Special Venting Systems

There are a few times when you may need a special type of vent for your specific system. Here are a few examples.

Circuit Vents

Places that have many fixtures, such as apartment buildings, may benefit from using a circuit vent system. This means that they can minimise the number of points of exit required for the many vent stacks of regular vent systems.

Each horizontal vent in a circuit system can be connected to as many as eight fixtures. You can connect multiple circuit vents, which works well in large buildings.

Chicago Loop

Because some fixtures have specific configurations, they may not be compatible with standard vent systems. As an example, some kitchen islands feature a drain line that cannot run horizontally above floor level. What do you do in this situation? Using a Chicago loop can be the answer.

A Chicago loop sees a vent pipe connected under the sink to create a loop above the sink’s floor rim. This leads right down into the floor of the kitchen. Then, the pipe can extend out horizontally to connect with the main venting pipe.

Studor Valves/Air Admittance

Rather than using a standard vent for your sink drain, you can use a studor valve. Check your local regulations about these types of valves as they are not able to be used everywhere. When water drains down the pipe, the valves open. This allows air in and releases pressure building up in the pipes. The downside of these is that they can get stuck closed and they do wear out rather quickly.

What Are the Signs Your Plumbing Vent Pipe Is Blocked?

You may not have even realised that you had a venting system in your plumbing. So, how will you know if the vents get blocked? When vents become blocked, this causes negative pressure to build up in the system. This will interrupt water flow.

Here are some signs to watch out for:

  • Water is draining very slowly.
  • Clearing the drain is ineffective.
  • Potent smells like sewage are coming up through the drain. If this happens your P-trap has likely emptied due to negative pressure.
  • Gurgling sounds are coming from your drains and pipes, with water coming out of another drain. The sound happens when air gets sucked out of your P-trap.
  • Stagnant water is sitting in your bathtub, sink or other drains.

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Unblocking Vents

The way you clear your vents will depend on the reason it is blocked. The best method for finding out what is blocking it is using a CCTV drains camera. This must be used by a highly-trained technician, such as one of our plumbers at Fixed Today.

We snake this high-tech camera down your drain pipes. It feeds back to us live images of the drain line so we can clearly see what’s going on. This helps us to come up with a solution specific to your problem.

It will also confirm whether there is something wrong with your vents or if the issue is related to something else. 

It is not recommended that you deal with vent issues yourself. If you suspect that you are having vent problems in your plumbing system, give us a call ASAP. We’ll be right over to check if your vents are blocked and fix the issue.

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