How to Vent a Toilet +Venting Options without a Vent

Toilets come with very simple mechanisms including a P-trap and a venting mechanism. This setup ensures that the toilet flushes properly, prevents the entry of sewer gases into the home and doesn’t get clogged up with time.

The venting system of your toilet is based on how liquids and gases work in terms of their weight and response to behavior. Since wastes and liquids are heavier than gases, they usually occupy the lower sides of the pipes with the gases occupying the upper sides of the same pipes. Venting allows a balance of pressure between them to allow the wastes flow to the drain and the gases to escape to the outdoors through the vent.

Why does a Toilet Need a Vent?

When you take a look at the design of your toilet, you notice lots of curves and a pool of water at the base of the toilet bowl. This pool of water acts as a seal to the drainage system whereby without it, awful gases would flow into the house. However, these gases need to be released since without a vent the toilet becomes a closed system. Therefore, the reasons your toilet need venting include the following:

Prevents toilet bubbling

When the toilet isn’t being used, it should be still without any running water or bubbles. While running water would point to a leak in the toilet tank, air bubbles coming into the toilet bowl would indicate poor venting. This is because air, lacking a way to escape to the outside, forces its way into the bowl and escapes as bubbles.

Allows proper flushing

With the right venting, your toilet allows water at a high pressure into the toilet bowl. The weight of the water forces its way past the P-trap and into the drain. If there is any type of obstruction in the drain, it will hamper this process.

For example, if there is a clog, it will take long for the water to get flushed. Another hinderance is a lack of venting. With air under pressure in the section immediately after the P-trap, the flow of wastes down the drain will be going against the air hence will lead to a large bubble flowing out of the bowl as the wastes flow down. This can easily mess up the toilet.

Keeps the water level in the toilet constant

The water at the bottom of the toilet bowl acts as a seal against sewer gases from the drainage flowing into your home. It should always be at a constant level which is the bottom of the P-tap. Without proper venting, air builds up pressure under the P-trap and will either push or suck in the water in the bowl. The result is either a high or low level of water in the bottom of the bowl.

In general, you can tell whether your toilet is correctly vented or not when it can’t flush correctly, has bubbles and the water level in the bowl keeps rising or falling.

Toilet Venting Steps

Venting your toilet depends on various aspects including the size of the pipes, the design of the toilet and the regulations in your area. Toilet venting depends on the rules set by the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC).

With toilet venting, there are various ways one can do it as follows:

1. Tie directly to the vent stuck

In most cases, the toilet drain pipe is run for a short distance then, as it drops towards the sewer in a vertical manner, a vertical vent is extended from this point upwards and into the roof where it’ll have an open end.

The waste connection is made with a sanitary tee whose sweep is directed towards the sewer and then the vent pipe is glued to the port that would be facing upwards. In this setup, you can also direct the waste pipe into a vent stack or soil stack and tie into the stack with a wye fitting with the latter facing downwards.

For this type of setup, the use of a wye fitting and sanitary tee is very important. While a wye fitting has a Y shape with a long and straight inlet port, the sanitary tee has a short curve on the inlet port.

For this direct kind of setup, the vent size can be reduced to 2 inches with the use of a reducing bushing glued to the vent pipe. However, such a reduction in the size of the vent pipe isn’t permeated in areas covered by UPC jurisdiction. This is because the UPC requires that there be a vent pipe in the home which is at least the same size to the sewer pipe. This is often the main vent stack in the house and the other vents would connect to it.

2. Connect the vent underneath the toilet

Another way to install a vent to your toilet is to add it to the vertical part of the waste pipe before the long-sweep elbow. This is best installed to a waste pipe which has a long-sweep elbow for the best results.

This installation is done with a reducing wye whose sweep points downwards with the elbows being used to change the direction of the vent pipe as required.

3. Tie in with a wye and street elbow

Another approach used in venting a toilet is by installing a wye into the horizontal part of the drain line with the sweep being towards the sewer. A 45-degree street elbow is then glued into the wye outlet then vented vertically into the wall behind the toilet or any wall close to the toilet.

A reducing wye is used to transition from a drain line 3 or 4 inches in size to a 2-inch vent then to direct the sweet of the wye fitting towards the sewer. This setup may seem complex but it’s actually one of the simpler ones.

4. Wet venting

Wet venting entails venting a toilet through another fixture and is permeated by both the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC) since it saves on space and time. Given that wet venting uses pipes with both air and water, the size of the venting pipe must be at least 2 inches in diameter for the venting to work properly.

A sink drain is used in most cases and the connection is made such that the sink drain is connected to the toilet water line with a reducing sanitary tee being used with its sweep towards the flow of the water. The outlet of the tee should point upwards and be perpendicular to the drain pipe.

Illustrations for the 4 ways in which you can vent your toilet are documented below.

How to vent a toilet diagram
Venting illustration by Hammerpedia

When venting a toilet, consider the following aspects:

  1. The size of the drain of the toilet
  2. The size of the toilet’s vent
  3. The length of the toilet’s trap arm

These will help determine the angles and sizes of plumbing supplies required.

As you vent your toilet and carry out any other types of plumbing, put the following tips in mind:

  • Lay the vent and drain pipes before the supply pipes to get the best results.
  • Always test the pipes and other fittings before permanently fitting them.
  • Given that drain pipes need to be slopped between 1/8 and ¼ of an inch per foot of horizontal travel, you should calculate the amount of vertical space available on the flow then use that to lay the pipes and other fittings.

With these aspects, you can be sure to have proper drainage in the plumbing system.

Toilet venting options Without a Vent

If your house has no venting pipe or it’s broken and can’t be fixed, you can still have the toilet performing correctly. The solution is in the use of Air Admittance Valves which are often called cheater vents since they perform the task of venting the toilet without the necessary structures found in normal plumbing vents.

The use of air admittance valves to vent toilets is a bit contentious and you should ensure it’s legal in your area before using one. However, we’ve found out that lot of these pieces of equipment are in use all around the country and the chances of it being illegal in your area is very low.

How can an air admittance valve be used to vent a toilet?

The workings of an air admittance valve is quite simple as it involves allowing air to enter the drain system and preventing air from the sewerage system from coming out of the drain and into the house. The valve does this by reacting to the pressure in the drainage system and the atmospheric pressure.

When the pressure in the drain is low, the valve’s seal will open by lifting and allowing fresh air to flow in and balance out the pressure.

Due to gravity, the seal closes by itself when the pressure inside the drain is equal to the atmospheric pressure outside the air admittance valve. In the closed position, no bad odors will flow outwards and into the house.

Basically, the air admittance valve derives its names from its main task which is admitting air into the drainage system. This prevents the problems associated with bad venting which include bubbling toilets and rising and dropping water levels in the toilet bowl.

How and where to install an air admittance valve

The small size of air admittance valves makes it possible to install it just about anywhere in the home. One such place to install it is under the bathroom or kitchen sink. You can also connect it to the sewer system in the basement or above the isolation in the attic. The most common location, however, is the vent of the toilet drain. Installed properly, air admittance valves are very reliable.

You can install the air admittance valve by providing a tee sanitary connection pipe with an adaptor. You then place the sanitary tee pipe in an upright manner or 15 degrees to the vertical plane. Follow this up by connecting the left and right parts of the tee pipe with the sewer pipe and then positioning the disconnected pipe to the ceiling. At all times, use Teflon tape with the fittings to obtain a tight fit for all the connections.

How to vent a toilet sink and shower

The best way to vent a toilet sink and shower is to use wet venting which is the method explained in the sections above. In wet venting, the sink drained is connected to the toilet water line using a reducing sanitary tee. The sweep of the reducing sanitary tee should be towards the flow of the water and the outlet of the tee is to point upwards. The tee’s outlet ought to be perpendicular to the drain pipe for the best results.


What is the ideal Toilet vent distance?

As per the regulations of the UPC, the ideal toilet vent distance is limited to 6 feet.

Are there self-venting toilets?

Yes. There are self-venting toilets although legislation still requires that the trap arm be vented again to be on the safe side.

Can a clogged vent cause a toilet to overflow?

Yes. A clogged vent can lead to an imbalance in the pressure of the toilet leading to an overflow.

Can a toilet shower and sink share a vent?

Yes. A toilet shower and sink can share a vent through wet venting.

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