Purpose of Toilet Vent Pipes

Maybe you’re in the middle of a DIY bathroom remodel, or maybe you’ve asked a professional to evaluate the plumbing of your new home – regardless, we bet toilet vents have come up in conversation.

These vents are easy to spot because they are exactly what they sound like; ventilation channels that run from your residence’s plumbing appliances, such as sinks, bathtubs, and, of course, toilets, up and out of the roof of your home.

Toilet vents are crucial to the painless performance of your plumbing and to a homeowner’s peace of mind.

Key Takeaways

  • Toilet vents are imperative to keeping sewage odors out of your home.
  • Plumbing ventilation systems keep your drains running smoothly.
  • P-traps catch debris and solids, as well as odors.
  • Vent caps and covers are recommended to keep your vents clear.

Toilet Vent Working or Not?

three images showing if the vent pipe does not work There are several ways to know if your toilet vents are not correctly installed or, even worse, if there is no ventilation at all.

  1. If you hear awful gurgling sounds when you flush
  2. If you have sluggish drainage with your fixtures
  3. Start to smell unpleasant odors

You may need to take a second look. Both could be caused by the lack of ventilation.

Operation of Plumbing Vents

Toilet vents allow air to enter behind the liquid moving through your drains, which create smooth flow throughout your home. The same air that helps your waste and water flow smoothly, also alleviates negative pressures and keeps your traps sealed.

image showing the pipe on the root and side of building, 4 circles with info The negative pressure is called siphonage and positive pressure is called back pressure. The balance of negative and positive air pressures in your drainage systems is imperative to an effortless and quiet plumbing system.

More importantly, a correctly installed toilet vent gives escape to sewage fumes that come from the horizontal sewage drains that run beneath your home.

These vents take the odors up and out of your roof, instead of giving them the chance to seep into your rooms.

Scenario of a Clogged Vent Pipe (My Story)

Let me share a story with you – when I was staying at my parents’ house for the holidays, I was smelling an awful odor in my bedroom. I thought to myself, whoa… that can’t be me, right?

Then, one day, as I was getting ready to wrap some Christmas gifts, I opened the storage closet adjacent to my childhood bedroom. It was like I was punched in the face with this nasty odor. This storage space, where my folks’ keep the holiday decorations and wrapping paper, had an open drain at the very back corner.

We realized during my parents’ recent bathroom remodel, the ventilation system had not been correctly installed, and therefore, unpleasant fumes were entering through that open drain and into my childhood bedroom.

Because nobody else stays in that room except when I come to visit, they hadn’t been aware of the issue.

As waste moves through the main sewage lines, vents draw air up and out. Without well installed toilet vents, you might have troublesome experiences like ours’.

Toilet Vent Connection to Main Plumbing

Toilet vents connect to the main drain, also called the stack, which should be about 4” in size and run vertically down your wall, to better aid in keeping drains unclogged.

Next you will see a secondary stack and branch drain pipes that carry water to your fixtures, and are often 1.5” to 2” in size. Vent pipes should be around 2” in size, and connect off of the main stack.

Different Types and Names

There are all sorts of vent types and names. Be sure to check the building codes in your locality to understand what venting systems are allowed and appropriate for your city.image showing six different types of vent pipes

True Vents

A true vent attaches to the main stack through the roof and has no water running through it.

Auxiliary Vents

An auxiliary vent attaches from your plumbing fixtures that may not be conveniently located to your true vent.

Common Vents

A common vent is used when two fixtures are on either side of a shared wall.


AAV or Air Admittance Valves allow air into your system when siphonage increases, then close with the help of gravity.

Wet Vents

Wet vents are drain pipes that can double as a vent, but can only be used vertically.

Loop Vents

Loop vents are ventilation tactics separate from all other stacks, and go up to the roof singularly from a fixture.

Types of Toilet Drain Traps

three images showing different drain traps For the vents to work properly, there should be 6 feet of distance between the vents and traps.

Traps, also called P-traps or S-traps, are the small round section of your drainage pipes just before the horizontal wall tube. They sort of look like the letters P or S, hence the name, or like a J, and can also be called the J-bend.

  • These traps hold water, which creates a kind of seal or dam, and acts as the barrier between odors entering your home.
  • It also collects debris, solids, and anything else that might accidentally fall down your drain.

That’s how engagement rings are found after falling down the sink; they can (luckily!) be caught in the P-trap before they wash into the main lines, never to be seen again.

But, each usage of your plumbing fixtures flushes that old water out and replaces it with fresh water in the J-bend. So, if that engagement ring does fall into the drainage depths, don’t run the water!

Vent Caps and Covers

Your vent pipes open out onto your roof and into the elements, so we suggest investing in a vent cap or cover, to keep debris and even small animals out of your drainage systems.image showing two different vent covers

Vent Caps

Vent caps are often larger and more prominent metal covering to your vent. They allow air to move freely and odors to leave your home.

Vent Covers

Vent covers, also called vent boots, can be found in rubber materials, and are installed more flush to your rooftop, providing less of a potential eye-sore.

However, rubber vent boots will contract and expand as temperatures rise and fall outside, and will more quickly deteriorate in the elements.

Detect Vent Cover Damage

You can tell if your vent cap or boot is damaged if you see water marks on your walls and ceilings in your bathrooms and kitchen, as well as shingle damage around your vent.

Outcomes of a Well Installed Toilet Vent

So, next time a plumber asks you about your toilet ventilation system, remember the following…

  • Vents pipes should be installed as a 2” PVC
  • The distance to traps should be about 6 feet
  • Your P-traps cannot be dry.

Well installed vents will give you…

  • Smooth drain flow
  • Vented odors from the main city line and septic tank
  • Lower drain noise

So if you have gurgling or clogging when you flush your toilet, or if you smell unpleasant odors, take some time to have a plumber check the vents.

The ventilation goes up and out of the roof of your home, so look into some vent covers or caps to keep your drains clear from outside debris.

If you take the time to have your toilet vents installed well, your plumbing systems will run perfectly.