Toilets are simple systems with two purposes. They flush to remove waste and prevent sewer smell in a bathroom.
Toilet venting helps with both because it controls air pressure in drain pipes. Heavier waste and liquids occupy the lower part of the outlet drain, while air stays in the upper parts. That way, air can flow out through the vent that goes up to the roof.
On the other hand, hard waste stays down and escapes through the drain line. This is how the standard air vent works, but there are alternatives.
Let’s see the basic ways to vent your toilet.
Why Does Your Toilet Need a Vent?
A toilet is a simple fixture — flush it, and it will send a waterjet to clean the toilet bowl. The air vent steps in when the waste enters the toilet drain pipe. The vent is just a pipe guiding awful odors out of your home, so you don’t feel the sewer smell in the bathroom.
It’s a critical function because your toilet would be a closed plumbing system without the vent.
The pool of water in your toilet bowl prevents sewer gases from returning to the bathroom, but they can’t stay in the pipes forever. The air vent is the solution because it sends gases out of your home through the roof.
But this is not the only thing air vents do. They play three roles in the plumbing system.
It Enables Proper Flushing
First of all, the vent pipe allows you to flush the toilet properly. Wastewater flows through the trapway after flushing, sucking smelly air down the pipes.
The air can’t go out without a vent, which means it would stay in the outlet drain to collide with the next round of waste.
Your toilet could still work, but it would deliver a noisy and dirty air bubble to the bowl every time you flush. That’s why your toilet needs a vent — to release air through the pipe and restore pressure in the system.
The Vent Keeps the Water Level in the Toilet Bowl
Your toilet bowl needs a consistent water level to remove waste and stop sewer gasses from returning to the bathroom. That’s why you always see a small pool of water on the bottom of the bowl. But this wouldn’t be possible without the vent and its ability to regulate air pressure.
The pressure under the trapway would be too strong without a vent. It would do one of these two things:
- Suck water from the bowl, leaving it to the minimum. In that case, you would keep noticing a sewer smell in the bathroom
- Push excess water into the bowl, making it look like overflowing
The average pool in the toilet bowl is the sign that your vent works well. You will know that something’s wrong with the vent as soon as you see the water level in the bowl dropping or rising.
It Prevents Water From Gurgling
A functional toilet doesn’t make strange noises. You can only hear the water running through the toilet drain pipe, but the sounds end in a few seconds. It’s another thing that the vent does — it prevents water from making unusual sounds.
Without toilet venting, you would keep hearing water gurgling in the toilet bowl. The reason is clear — air wouldn’t find a different way to escape. It would return to the bowl, causing funny air bubbles after flushing.
Basic Toilet Venting Options
Now that you know the purpose of the vent, it is time to check out the basic venting options. We recognize four types:
1. Straight Vent Connection
Most toilets have a drain pipe that stretches horizontally. The toilet drain pipe goes down at one point because it delivers the waste to the sewer. In this case, the vent pipe takes the opposite turn and goes up to the roof to release air.
This structure needs a wye fitting with a tee sanitary connection pipe. Together, these two components help the drains go in opposite directions — one line to the sewer and the other to the roof.
2. Venting Connection Under the Toilet
Another popular choice is to establish a vent connection under the toilet. In this case, you can place the vent on the vertical waste pipe before it reaches the elbow’s turning point.
You’ll need a reducing wye to make this work because it’s the only way to attach the vent adequately. The wye allows you to change the vent’s angle, so it can part ways with the toilet drain pipe when needed.
3. A Street Elbow and a Wye
You can create a toilet vent by connecting a street elbow to the wye. The first task is to place the wye horizontally against the outlet pipe. After that, you can add a street elbow with a 45-degree angle to the wye.
The two parts can hold the vent pipe in a vertical position, allowing it to stand still behind the bathroom wall. This vent often resides in the rear wall behind the toilet, but you can also install it in the sidewall when close enough.
4. Wet Venting
The international plumbing code recognizes wet venting as another way to vent a toilet. This model uses only one pipe to transfer waste and air. However, installing a wide pipe (at least two inches) is essential to help both elements pass through.
Wet venting connects multiple fixtures in the bathroom, creating a common venting point. Most homeowners use a sink drain as the connection point for their toilets. They do it because it’s easy to attach it to the toilet via the sanitary tee pipe.
The pipe’s entrance elbow is facing the water flow, while its outlet goes up to oppose the waste line. The benefit of wet venting is its ability to preserve space, making it ideal for all bathroom sizes.
How to Vent a Toilet Without a Vent
Air admittance valves serve as a popular alternative to traditional toilet venting systems. This way to vent a toilet is somewhat controversial, but it remains a widespread option with many benefits.
What Is an Air Admittance Valve?
An air admittance valve is a tool that reduces negative pressure in the waste disposal system. Air admittance valves operate by releasing pressure in the pipes. They rinse water entering the system rather than relying solely on gravity.
Some people call it the cheater valve because it’s not legal in all countries, but there is no uniform plumbing code. However, the truth is that cheater vents have practical value in homes where installing standard vents is impossible.
The air admittance valve relies on a simple venting mechanism that doesn’t require as much space as traditional vents.
How Do Air Admittance Valves Work?
Air admittance valves control pressure in plumbing systems. As the name suggests, this valve admits air into the plumbing lines. It recognizes a low-pressure zone in the pipes and reacts by opening a seal. It’s just a mechanical device that lets the air enter the toilet drain line.
The pressure restores, and the mechanical seal closes due to the power of gravity. In this case, gases can’t go in or out of the air admittance valve. The pressure keeps the balance, so your toilet can flush as usual.
The air admittance valve remains in its original position until it feels the pressure is dropping again.
Are Air Admittance Valves Legal?
While there is no uniform plumbing code to answer this question, we can note that many regulatory bodies approve of cheater valves. That’s because cheater valves have several benefits:
- They reduce drainage system installation costs
- They minimize the risk of roof leakages
- They make roofs eye-pleasing by eliminating unnecessary holes and vents
On the other hand, this mechanism cannot guarantee relief of positive pressures. It’s the downside that makes air admittance valves illegal in some countries.
The solution comes from the International Residential Code. This document says that “at least one vent pipe shall extend to the outdoors to relieve the system’s positive pressure.”
How to Vent a Toilet? Choose the Right Mechanism
You can install the air admittance valve, but there are other alternatives. Before you decide how to vent a toilet, you must think about the following features:
- The length of the drainage system and waste pipes
- The height of the air vent
- The distance between the toilet and the sink drain
- The availability of the air admittance valve
If you want to vent a toilet properly, consider all these features and decide accordingly.
The Bottom Line
Your bathroom can’t work without toilet venting, so it’s important to consider all options. There are four standard mechanisms to vent a toilet, but air admittance valves are becoming a widespread alternative.
What you choose depends on the structure of your plumbing system, so make sure to give it a thorough check before picking the right venting option.
What happens if the toilet is not vented?
If your toilet is not vented, it cannot flush and dispose of waste as usual. Besides that, it will create strange gurgling sounds and allow bad odors to go back to the bathroom. Finally, your toilet bowl is losing water without proper ventilation.
Does every toilet need the vent pipe?
Yes, every toilet needs a vent pipe to work well. Without it, your toilet could not get rid of waste and debris. The toilet needs venting to balance the atmospheric pressure, enable the flush system, and prevent awkward smells.
How to vent a toilet without going through the roof?
Some buildings can’t vent through roofs, but they can use alternatives. Building codes in some countries allow you to install the main stack in the wall, but you’ll need to double-check with your plumber.
Air admittance valves are the most popular alternative to roof-based vents. The cheater valve serves the same purpose as the air vent, but it has a slightly different mechanism. It doesn’t rely on gravity but rather creates pressure to balance liquids and gases.