How to Properly Vent Your Pipes

sink drain

So, you’re ready to remodel your kitchen or bathroom and realized that new plumbing is in order. If this isn’t an issue you’ve run into before, you might find it a little more difficult than most other DIY projects. Before panicking and calling a plumber, know that there are simple ways to ensure your pipes are properly ventilated.

A quick internet search for “plumbing vent diagram” will bring up multiple ways to tackle this issue, but how do you know which one will work for your home? What are the pros and cons of each system? Whether it’s a new sink, tub, or toilet, here’s how to properly vent your pipes.

Understanding the Plumbing Vent

Visualizing the pipes inside your wall is made easier if you start from where you can see. You’ve opened up the cabinets under a sink before to see the P-shaped tube directly underneath the drain, right? It’s called the P-trap, and it starts the sewage/ventilation process.

These drain pipes connect to showers, sinks, tubs, and other appliances in order to carry water away after you’re done using it. From there, the water moves into slightly larger drain pipes as they continue to connect and make their way to the stack. Soil pipes do the same for toilets.

vent diagram

The stack pipe leads the whole way out through your roof and further underground in the opposite direction to main sewer lines. Water and waste head down the pipe, while gasses are vented up and outwards. The stack also allows fresh air in to keep water running smoothly through your piping.

Without the stack to properly ventilate things, your home would reek and fill with noxious sewer gasses. To help the stack do its job, ventilation pipes are often added to fixtures so that gasses can freely move away from your home while using fresh air to move sewage freely.

It’s not something most homeowners like to think about, but it is a critical part to any household. Whenever you’re renovating, fixing your plumbing, or just adding a new fixture, it is vital that you make sure this system functions properly.


Types of Vents

There are four main types of ventilation used in piping. They are:

  • The true vent
  • A re-vent pipe
  • The common vent
  • And the loop vent

The true vent is aligned vertically and attaches to your drain line through the roof. This is best implemented if a fixture rests close to the stack and the top floor of your home, allowing the stack to serve as a vent. True vents also have no water running through them. While the true vent is simple, it isn’t always a possible solution since fixtures are rarely located so close to the stack.

Re-vent pipes, otherwise known as auxiliary vents, attach to the drain line near your fixture as they run upwards and over the main vent. They can attach right behind your fixture or horizontally to the drain line. These are excellent options when your sink is too far away from the main stack.

In the event that you have another fixture on the opposite side of the wall, you probably want to use a common vent. This allows both drain lines to tie together in a sanitary cross. You can usually find these on back to back sinks.

The loop vent is a solution for many freestanding sink codes. It loops up an around before connecting to the drain pipe, allowing ample ventilation to take place just behind your fixture. There is also a wet vent, but these are mostly reserved for tubs that sit close to a stack and may not be allowed by your locality’s code.

As an alternative to venting altogether, some codes allow for air admittance valves. These allow air to enter as waste drains, then rely on gravity to seal back up before any gasses can make their way back into the room. These are relatively new, so make sure to check with your area’s codes before buying any.


Placing Your Fixture

placing fixture

Whichever ventilation system you choose to employ, it is equally important to place your fixture a certain distance from the vent pipe. This area is called the critical distance and involves a few calculations to figure out. The size of your pipes, the type of fixture you are installing, and the number of fixtures that are wet vented in your home all play a part in determining that measurement.

During this phase, it is highly recommended that you consult a plumbing inspector after measuring the length of your pipes. They can also tell you how to properly vent your pipes, pointing out which one of the systems works best while satisfying local code.


Installing the Vent

Unlike drainpipes, vent pipes do not need to slope. You can run them level so long as there are no obstacles to work around. The main goal here is to ensure the vent piping will remain dry. That’s why most diagrams depict them running vertically, making sure that no water can back up into the system.
The re-vent is the only exception since it runs horizontally. However, it needs to be at least six inches above your fixture’s flood level to keep from getting wet. On a sink, that would be either the rim or overflow hole.


A Note on the Main Drain

When installing your vents, it’s highly recommended that you plan out your drain lines to minimize the risk of clogging. Both kitchen (1-1/2 inches) and bathroom (1-1/4 inches) are smaller than the rest of the drain system on purpose. They lead into larger branch drain pipes, which lead into the 4-inch stack.

Since the main stack is vertical, it’s a rare occasion that this pipe clogs. While other pipes connecting the stack will need to be horizontal, making them larger allows an ample amount of water to flow through them freely. This is also a good time to have a professional check your main drain line, which resides underground, for any clogging.


Useful Diagrams

To help you better visualize what these piping systems look like, we thought it might help to incorporate a plumbing vent diagram. The image below illustrates s typical bathroom with multiple plumbing vents. There’s even a wet vent included that connects to the bathtub.

tub patterns

As you can see, the true vent aligns with the stack just behind the toilet. However, the sink is placed further away. Therefore, a re-vent was added to ensure that sewer gasses could escape.

This next image shows various types of vent piping behind a sink, giving you a more accurate idea of what those might look in your own project. Depending on the layout of your home, one of these will more than likely work best for you.

sink vent diagram

This image clearly displays what the loop vent looks like, which you may need to use if your sink is too far away from the stack for a re-vent pipe. It also shows what the sanitary cross would look like if you happen to have a sink on the other side of the wall. Both sinks connect at one point, sharing a common true vent to the stack.

From the side angle, it becomes easier to imagine what these pipes might look like behind your bathroom or kitchen walls. Notice how the main vent and waste pipe remain separated behind the sink, only connecting via the attached went pipe. This revert is at least six inches above the overflow line and properly connected with a drainage T.


Extra Info on the Air Admittance Valve

In the event that your walls do not leave enough space for any of the above vents, then the local code may allow you to opt for an Air Admittance Valve (AAV). This one-way valve is designed to allow air into the plumbing when negative pressure is developed from draining. After allowing air in, it seals itself back up to keep odors and gasses out.
These devices normally attach underneath the sink just past the trap, ensuring amply air makes its way into your pipes. Keep this method in mind if you tear into the wall and discover that there is little room for a vent pipe. Always check your local codes with a plumbing inspector to make sure you can use an AAV, though.


Venting Your Pipes

venting pipes

Well, that’s all there is to it. Now you know the ins and outs of proper sewage pipe ventilation and are ready to tackle this aspect of your renovation project. Remember to use the best setup possible depending on where your fixture is and to refer back to these diagrams to ensure you’re properly setting up the vents.

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