What is a Plumbing Air Vent and How Does It Work?


If you have a plumbing system in your home, then you likely have air vents. Air vents are an important part of the system, as they allow air to flow into the pipes and prevent vacuum pressure from building up. However, if something goes wrong with your air vents, it can cause serious problems for your plumbing. In this blog post, we’ll discuss everything you need to know about air vents, including how they work and what can go wrong.

What is a plumbing air vent?

A plumbing air vent is a necessary part of any home’s plumbing system. It allows air to enter the system, which prevents a vacuum from forming and causing water to be drawn out of the system. Without an air vent, your home’s plumbing system would not work correctly.

If you have ever seen a house that has a plumbing vent pipe sticking out of the roof, then you have seen a plumbing air vent. These vents are usually white and made of plastic or metal. The size of the vent will depend on the size of the plumbing system it is servicing. Most homes will have several of these vents, one for each plumbing fixture. Below is a plumbing vent diagram that shows a visual representation of the plumbing vent layout.

Plumbing Vent Diagram

P016C - Drainage, Waste and Vent (DWV) System_300dpi
Credit to Mr. Fix-It

Why is a plumbing air vent important?

A plumbing air vent is important because it allows air to enter the system and allows sewer gases to escape. In other words, it allows the atmospheric pressure to equalize on both sides of the p-trap. Without an air vent, your home’s plumbing system would not work correctly and your house would end up smelling like sewer gas. If you smell sewer gas in your house, you will want to have a plumber investigate the plumbing vent to ensure it’s installed and functioning properly.

How does a plumbing vent work?

As wastewater leaves your fixtures, it creates a low-pressure area in the drainpipe, which causes air pressure to push on the trapped water in the p-trap. The trap seal prevents any scent from escaping into your home while also preventing sewer gases from entering the home through the drain opening. If you have a blockage further down in your drain piping, it will create a strong siphoning action that will cause water to drain out of the lowest point in your system.

Types of Plumbing Vents

Auxiliary Vent (also called re-vent pipe) – An auxiliary vent is usually made out of PVC and comes in 8″, 10″, or 12″ sizes. Auxiliary vents are commonly used to vent washing machines and bathroom sinks, but today’s codes require a true vent for these fixtures. If it is not possible to run a true vent from the fixture, then an auxiliary vent can be used.

True Vent – A “true vent” is a pipe that runs directly from the plumbing fixture to the outside of your home, and it’s usually made out of PVC.

Loop Vent – A loop vent is often used when fixtures are located directly above each other. For example, a sink and a toilet in the same room could both be vented through a single pipe with a loop. This type of vent saves money on installation, but it’s important to remember that the plumbing system will not function properly if the loop is broken.

Common Vent – A common vent is used to vent multiple fixtures through a single pipe. For example, a bathroom and a kitchen could both be vented through a single pipe. This type of vent requires certain conditions to be met and should always be installed by a professional.

Air Admittance Valve – An air admittance valve (AAV) is used to allow air into the system so the fixture can drain but it shouldn’t be confused with a vent. An AAV allows extra air into the plumbing system, which causes negative pressure and pulls odors up through floor drains. An AAV should not be used in place of an actual vent because it cannot handle the same volume of air.

Common plumbing vent problems

1. Slow Draining Sinks and/or Toilets – If you notice either of these issues happening at your home, it could signify a blockage is occurring somewhere in your drainage system. The blockage may not necessarily be at the fixture itself, but somewhere further along in your piping. This is why it’s important to have your venting system examined by a professional.

2. Water Heater Issues – A clogged vent can cause pressure buildup on your water heater which leads to water leakage and possibly cracking on the tank itself. You may notice that your hot water only lasts a few seconds, or will go cold if you flush the toilet while waiting for hot water.

3. Musty Smell – If your plumbing vent is blocked, it can cause sewer gas odors to rise into your home and pool in low areas such as bathrooms and laundry rooms – particularly if they’re on a lower level of your home. If you notice a musty or earthy smell coming from your drains, chances are that you might have sewer gas building up in the system and need to call a professional for help.

Why do I need to test my plumbing vent?

Your home’s plumbing vents should be tested at least once every two years, and as needed following any renovations or new fixture installations. Blocked vents can lead to sewer gas odors inside the home, as well as water damage to your home and its contents.

How do I know if my plumbing vent is clogged?

There are a few signs that can indicate your plumbing vent is clogged. If you notice any of the following, you should call a plumber to have them check your vent:

– Your plumbing fixtures are making strange gurgling noises.

– You can smell sewer gas in your home.

– Your toilets are constantly overflowing.

– Your drains are backed up.

– You have water in your basement or crawl space.

If you notice any of these signs, it’s important to call a plumber right away. A clogged plumbing vent can cause serious problems for your home’s plumbing system.

How do I know if my plumbing system has an air vent?

The easiest way to determine if your plumbing system has an air vent is to look for a vent stack on the roof of your home. If you don’t see a vent stack, your plumbing system may not have an air vent. You can also check the plumbing fixtures in your home for an air vent. Most plumbing fixtures will have a small hole on the top of them that allows air to enter. If you don’t see any holes, your plumbing fixture may not have an air vent.

If you are not sure whether your plumbing system has an air vent, you can call a plumber.

How to prevent plumbing vent issues?

It is said that “prevention is better than cure” and that applies to your plumbing vent also. If you take good care of it, chances are you won’t end up in an emergency situation. Besides, this is easy to do.

  • You should always ensure that you don’t dump any unflushable material in the commode else it will create unnecessary clogging issues.
  • You should attend to clogging issues immediately before they become big.
  • Always keep the contact details of a professional handy.

The Final Word

Plumbing vents are crucial in ensuring the smooth running of your home or workplace’s plumbing system. It ensures the drains flow smoothly in your home and bad odors never enter the home. It is important to keep the plumbing vents functional to prevent issues such as clogging.

Leave a Comment