Can You Use A Wye For Venting?

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 horizontally running drain line.

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

If you're wondering about the application of the wye fitting in plumbing systems, wonder no more. We'll discuss how wye is used in toilet and sink plumbing installation and 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 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 for better airflow. The extended passage from the wye restricts the airflow resulting in poor wastewater movement.

The following 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 must consider the type of vented system and the local building codes and regulations.

To ensure you are not violating any code on the design and installation of plumbing systems, please look at 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; you can only use one to replace the other, but they have distinct functions. You cannot use one in reserve for the other without changing the entire plumbing design system.

This video can give you insights into their differences and uses:


A wye is used when splitting or diverting a flow in a specific direction. It has a Y-shaped 45-degree angle 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.

Different types of wye fitting exist, including traditional wyes, manifold wyes, double wyes, and accurate 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 less directional than the wye.

The tee vent's 90-degree angle diverts flow but slower. The liquid tends to drop faster with a tee vent because of the curve. 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 component 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 by one of the venting methods specified in this chapter.

There are many toilet venting methods, including standard 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, 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 wye size 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 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 wye size depends on which U.S. plumbing code you will follow.

The IPC 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 move solids and wastewater out of your drainage system properly.

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

Several signs 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 they need to exit up and out the roof or in an open area outside your home.

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 bathroom 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 multiple fixtures 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.

The fixtures are 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 for a full explanation of how a wet vent system works:

Wrapping Up

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

We hope this article has given you an idea of how to use a wye fitting for your plumbing system.

For more readings on plumbing and HVAC systems, check out these articles:

Should Air Be Coming Out Of My Condensate Drain Line?

How To Make A Plumbing Loop Vent

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