Can You Use A Wye For Venting?

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If you are in the process of installing a plumbing system, you may be wondering about your venting options. Can you use a wye fitting for venting? We did some research and here's what we learned.

You can use a wye fitting for venting when installing a drain line that runs horizontally.

A wye can be used as long as it meets the appropriate building code and regulations.

If you're wondering about the actual applications of the wye fitting in plumbing systems, read on below. We'll discuss how wye is used in toilet and sink plumbing installation and discuss the importance of vents in your home.

Y shape of pvc plastic pipe fitting and plastic corrugated flexible hose, Can You Use A Wye For Venting?

Wye Fittings For Venting

Laying down a plumbing system is like a puzzle. You need to be able to come up with an effective pipe system arrangement that ensures proper water and air pressure flow.

In many plumbing systems, a wye is often an essential connection to divert the flow of fluids or gases.

Can you use a wye for venting? Yes, you can use it in venting horizontal drain lines, but take note that it is not always the appropriate choice.

There are instances when the venting system arrangement is not working because it restricts the airflow into the pipes.

Take the picture below as an example. It shows the correct and incorrect placement of the wyes, tees, and 1/8 bends in a horizontal plumbing drain line.

The first picture shows the need to switch to a sanitary tee to allow better airflow. The longer passage from the wye restricts the airflow resulting in poor wastewater movement. 

The next picture shows the sanitary tee causing a backflow. Therefore, switching the pipes to a different angle and using a wye and 1/8 bend improves the flow of both wastewater and air.

When Should You Use A Wye?

A draining wye pipe

Using a wye will depend on the specific requirements for venting. You will need to consider the type of system being vented and the local building codes and regulations.

To ensure you are not violating any code on the design and installation of plumbing systems, you can refer to the 2021 version of the International Plumbing Code (IPC).

When reviewing the IPC, you can go straight to Chapter 9 which discusses regulations on various venting system arrangements.

What Is The Difference Between A Wye And A Tee Vent?

A wye and a tee may seem alike but they have very distinct functions. You cannot use one in replacement for the other without changing the entire plumbing design system.

The video below can give you insights into their differences and uses.


A wye is used when you need to split or divert a flow in a specific direction. It has a Y-shaped 45-degree angle that connects a horizontal drain line to a vertical vent stack.

A wye transfers the flow from vertical to horizontal, or horizontal to vertical.

Check out this wye white PVC 1.5 inch on Amazon.

Why is it called a wye? It is called such because of its characteristic "Y" shape. It has a single inlet called a "run" pipe and a two-outlet "branch" pipe.

There are different types of wye fitting, including traditional wyes, manifold wyes, double wyes, and true wye fittings.

Tee Vent

Similar to the wye, a tee vent or a sanitary tee is also used to divert flow, but the movement of the water in a tee is not as directional as the wye.

The tee vent's 90-degree angle diverts flow but not as smoothly. With a tee vent, the liquid tends to drop faster because of the angle. Consequently, this allows better airflow compared to the wye.

A tee vent has a horizontal branch that connects to the drain line and a vertical branch that connects to the vent pipe.

Check out this 2-inch sanitary tee white PVC on Amazon.

Can You Install A Wye Vertically?

Installing a wye vertically is often frowned upon because it can create a siphon effect.

If you put together a 45-degree elbow and connect a wye to a vertical drain, pressure can suck the water out of the trap and create a siphoning effect.

This type of vertical setup is only often applied in Y strainers when installed in a pressurized gas, liquid, or steam pipeline.

How Do You Vent A Toilet?

Plumbing building contractor installing plastic drain pipe in the floor section for a luxury custom house

Every toilet requires a vent pipe and there's usually a size requirement depending on your local code and regulations.

IPC 901.2.1 regulation reads:

"Traps and trapped fixtures shall be vented in accordance with one of the venting methods specified in this chapter."

There are many methods to vent a toilet, including common venting, circuit venting, and wet venting.

To help you out, we found this very detailed guide on how to do a simple conventional vent.

Here's a video on how to vent and plumb a toilet using a wye with 45 sized to the local code.

Vertical Vent On A Toilet Using A Wye With 45

Here is the overview of the design:

  • A 4-inch closet flange connects to a short 4-inch PVC pipe
  • The pipe drops to a 4 x 3-inch closet bend, which is 4 inches on the inlet and 3 inches on the outlet
  • The outlet connects to a long PVC that eventually meets up with a wye (the size of the wye should follow local code)
  • The wye's position is directly under a wall to allow you to connect it to a vertical vent
  • The vertical vent can either connect to the home's venting system (if there is any) or through independent installation, which means the vent will go right through the roof

The size of the wye to use depends on which U.S. plumbing code you will follow.

There is the IPC, which was mentioned earlier in the article, and the Uniform Plumbing Code (UPC).

If you're following the IPC, the size of the individual vent should be 1.5 inches so you will need to use a 3 x 3 x 1.5 wye with a 45.

The UPC requires a minimum of a 2-inch individual vent, so you will need to use a 3 x 3 x 2 wye with a 45.

What Happens If A Toilet Is Not Vented?

A vent allows air pressure to escape from your plumbing system. This means that without it, you will have problems with how wastewater moves through your plumbing system.

A toilet that's not vented or poorly vented won't be able to properly move out solids and wastewater out of your drainage system.

This means your flush will not work properly or you will experience frequent clogging. This also means that smelly and harmful sewer gases can get inside your home.

There are several signs that show your toilet is not properly vented:

  • Bubbles are showing in your toilet bowl even if you did not flush
  • There are changes in the water level of the toilet bowl even if you're not using it

Vents safely carry sewer gases out of your house, that's why it needs to exit up and out the roof or in an open area outside your house.

Your toilet and sink can share one vent so with proper plumbing design, you can have a wet vent with the sink connected first and then the toilet last.

Other fixtures in your home that require vents include the bathtub, washing machines, and kitchen sink.

What Is A Wet Vent?

A wet vent system installation is used if you have more than one fixture that you need to connect to the vent. The most common fixtures for wet vents are the sink and the toilet.

This type of vent is filled with water and is constantly under pressure.

When installing the fixtures, it's usually arranged in a specific order to ensure that the wastewater and other materials can flow freely and efficiently.

Wet venting is often used in commercial establishments or small residential areas with limited plumbing spaces. With careful planning, it can be cost-effective, safe, and effective.

Check out this video below for a full explanation of how a wet vent system works.

Wrapping Up

To wrap up, you can definitely use a wye for venting as long as you follow your local IPC and UPC regulations.

Thank you very much for reading through. We hope this article gave you an idea of how to use a wye fitting for your plumbing system.

For more readings on plumbing and HVAC systems, you can read further with these articles below.

Should Air Be Coming Out Of My Condensate Drain Line?

How To Make A Plumbing Loop Vent

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