How To Vent A Toilet Without A Vent: The Ultimate Guide

Installing a new toilet can be tricky when you don’t have a vent. Luckily, getting rid of toilet venting problems needn’t require major construction work. The issue is cheaper and easier to solve than you might think.

You can vent a toilet without a vent by installing vent ducts to get the fumes out through the roof. If that’s unfeasible, you can use an air admittance valve. Air admittance valves let air flow into your drainage system without letting odors leak back into your home.

Does A Toilet Need To Be Vented?

All plumbing fixtures in your home, including the toilets, need to be vented. The required vent size may vary from one city to another, based on the local codes. Generally, though, the vent size should be at least 1-1/2 inches. Wondering why you need it? Check out the reasons below.

To Avoid Gurgling Noises 

Toilets gurgle when negative air pressure builds up inside the drain pipes. The negative pressure is an indicator of poor ventilation and abnormal suction in the line. 

This negative pressure when there is poor airflow, and the air accumulating in the pipe will have to come out eventually. Considering that it can only get out the same way it got in the plumbing system, it will return through the toilet (and other fixtures).

You may hear these gurgling sounds when you’re flushing the toilet or see the water in your toilet bubble and gurgling when you’re using the sink or shower. Alongside the noise, offensive odors may also come out of your bathroom.

To Maintain Water Levels in Toilet Constant

In a plumbing system, the vents ensure proper airflow and help drainage. Without them, the system will create a siphoning effect that can draw the water from the traps. 

Plumbing traps are bent portions of pipe (the toilet has a built-in trap) that trap a small quantity of water. The water seals the sewer gas coming from the drain system into the drain pipes, preventing it from leaking into your home.

When the toilet lacks ventilation, the siphoning effect could cause the water level in the toilet to drop. The trap may not be sealed completely, and offensive sewer gas can leak back into your house.

To Allow for Proper Flushing

Lastly but equally important, a toilet without a vent may experience flushing problems. That’s because of a poor flow, which, combined with the gurgling and bubbling, could send the waste back. Another issue could be a too weak suction power that requires repeated flushes to get rid of the waste. It is needless to say that each of these situations is less than ideal.

How Does a Ventilation Process Work in Toilets?

A toilet drain vent works by removing sewage and greywater from your home or building. It also regulates the pressure in the pipes so that the wastewater can flow without impediment. Here’s what happens.

1. Flushing Creates Positive Pressure

When you flush the toilet, the wastewater flows through the drain pipe. The air inside the pipe has a neutral pressure compared to the surrounding atmosphere, but the water running through the pipe compresses the air, creating positive water pressure.

2. The Running Water Creates Negative Pressure

The positive pressure created by flushing needs to be released. As the column of water travels down the pipe, the pressure transforms from positive to negative. This pressure fluctuation inside the drain system can create a siphoning effect that can suck out the water from the toilet trap.

Without water in the trap, the sewer gas can leak back into your environment. Not only will you have to deal with nasty odors, but sewer gas is actually noxious (and potentially life-threatening if it manages to accumulate into your house).

3. The Toilet Vent Regulates Pressure

The toilet vent lets air inside the drain pipe. This air will follow the water column after flushing, preventing negative pressure from building up.

By preventing the negative pressure, the toilet ventilation pipe helps in preventing siphoning but also stops positive pressure from building up again.

As opposed to siphoning, an excess of positive pressure can push the wastewater back into the fixture, breaking the trap seal. This would result in serious hygiene issues and difficulty in flushing the toilet. Thus, the importance of a proper plumbing venting system for your toilet.

5 Different Ways to Vent a Toilet

There are four types of toilet vents that you could add to your plumbing system. Let’s check them out.

True Vent

The true vent is the most common plumbing vent system, similar to all other vents in your home. It consists of a vertical pipe (or vent duct) connected to the plumbing system and running through the walls all the way up to the roof.

True vents are so popular because they ensure proper airflow while also getting sewer gas out of your home through the highest point. Thus, there is no risk that offending odors will leak back in.

Common Vent

Common vents are similar to the true vent, but instead of serving one fixture, they serve two fixtures located on opposite sides of the same wall. For instance, your bathroom and laundry sinks could share a vent if you’ve placed them back-to-back on the same wall. The common vent is connected to the stack with a sanitary cross.

Stack Vent

This type of vent system can vent one or more fixtures through the soil or waste stack. It basically is an extension of the waste stack above the highest horizontal drain connected to the stack, allowing air into the system.

Auxiliary Vent

Also called re-vent pipe, the auxiliary vent connects the drain line to the main vent pipe through an additional length of pipe. This method is often preferred when adding a new fixture into the home, as it doesn’t require you to run a new vent through the roof.

Air Admittance Valve

An air admittance valve isn’t a vent in the true sense of the word, but it still allows air into the drain system while preventing sewer gases from leaking back into the house.

This valve is installed under or next to the fixture and opens when wastewater drains. Once the flow stops, the valve closes. Air admittance valves can be individual (installed on each fixture), or one valve could serve several fixtures.

They represent an ideal way to vent a toilet without a vent, but also other fixtures in your new bathroom, laundry room, or kitchen.

The Ideal Way: Air Admittance Valve For Toilet

An air admittance valve can solve all your toilet venting problems quickly and effortlessly. You only need minimal plumbing skills to install it and won’t have to drill holes through your roof. Follow the quick steps below to install one on your toilet. 

Where to Install an Air Admittance Valve?

Air admittance valves are placed between the fixture’s trap and the drain line. For this reason, you will have to cut a portion of the drain pipe and replace it with a sanitary tee. You can then install the valve on the tee’s open end.

Toilet air admittance valves are generally made of plastic or PVC and come in different sizes. You don’t have to go for the biggest size unless you’re installing it on a heavily used toilet. 

Generally, a mini valve capable of handling about 120 gallons of water per minute is sufficient for a guest toilet. A maxi valve can tackle up to 507 gallons per minute and is a perfect choice for the main toilet. 

Vent Toilet With Air Admittance Valve in 7 Easy Steps

1. Gather the necessary tools and materials

Installing an air admittance valve doesn’t require advanced plumbing knowledge, and you could complete the task successfully even if you’re a beginner. Before starting, make sure to have the following at hand:

  • Hacksaw
  • Sanitary tee
  • PVC glue
  • Deburring tool
  • Miter saw (optional)
  • PVC reducer 
  • PVC pipe
  • Pipe thread compound
  • Pliers
  • Rag

2. Locate the drain pipe

A toilet drain pipe is located on the floor beneath the toilet. You’ll have to remove the toilet bowl if it’s already installed, and, in some cases, you may also have to lift some floorboards and floor coverings. 

After you’ve removed the toilet, trace the drain until you find the main pipe (the large, 4-inch pipe).

3. Cut the drain pipe 

You will have to install the air admittance valve on this pipe; thus, you must cut a section of it and install a sanitary tee.

Cut through the drain line with the hacksaw (a circular saw with a plastic blade could speed up the work), about four inches from where the drain line connects to the drain stack. The 4-inch distance is a general number, but your local codes may require you to locate the valve at a certain distance. For this reason, you should consult your local plumbing codes before cutting.

If you don’t have sufficient space to install the tee vertically, you can cut the pipe at an angle of no more than 15 degrees with a miter saw.

Once you’ve removed the pipe section, use the deburring tool to smoothen out the edges and prepare them for the tee.

4. Install the sanitary tee

Push the tee in the space you just cut out, making sure that all edges connect. Seal the tee on the pipe with PVC glue or plumbing cement. The third inlet must face upward, so pay attention to the placement when you’re installing it.

When you’re done, you can reinstall the drain pipe from the tee to the toilet flange and seal it with plumbing cement or PVC glue.

5. Install a PVC reducer

Not all air admittance valves will require a PVC pipe reducer, but some will. Measure the diameter of the tee’s inlet and the size of the valve. If necessary, you can install a reducer to change the pipe’s diameter from three or four inches (depending on the fitting you installed) to the size of the air admittance valve, which is generally between 1-1/2 and 2 inches.

More often than not, the toilet specifications will determine the type of air admittance valve you need to install.

6. Install the air admittance valve 

Once you’ve reduced the pipe diameter, install a new section of PVC pipe extending at least four inches above the last turn of the toilet’s trap (this is the last turn before the water flows from the bowl into the drain line).

Cut the pipe and smoothen its edges with the deburring tool; this placement will see the valve just under the toilet tank.

You can now install a male fitting and cover its threads with a pipe thread compound. You can then mount the air admittance valve, tightening it by hand. Once it’s hand-tight, turn it one more full turn with a pair of pliers to ensure a tight fit. Remove any excess thread compound with a rag.

7. Install the toilet and test the valve

You can now install the toilet back onto the flange, flush, and check for leaks. Also, pay attention to the sounds coming out of the toilet. If you hear gurgling, the air admittance valve doesn’t work as it should. In this case, it is best to hire a plumber to fix the issue.


While installing an air admittance valve isn’t overly complicated, you still need some plumbing skills. If you have further questions, check out the answers below.

Will a toilet flush without a vent?

A toilet can flush even if it doesn’t have a vent. However, there are a series of problems you could experience. 

The most likely is that the negative pressure will siphon the water out of the trap. You’ll see the water level in your toilet bowl drop, and the sewer gas will be able to leak into your house. 

Another problem is when positive pressure builds in the pipe. Positive pressure will push wastewater back into the fixture, meaning that you might have to deal with a pool of human waste in your bathroom. Since this isn’t something to look forward to, you should install a vent or air admittance valve.

Does a toilet need a vent stack?

All toilets need some kind of venting system, even if it isn’t a vent stack. Vent stacks are the most reliable and popular venting systems, though, as they let sewer gases escape your house through the roof.

Is the air admittance valve reliable?

Yes, air admittance valves are as reliable as any other venting system. Most valves have a lifespan of about 30 years (or 500,000 cycles) and are very easy to replace if they fail. 

The only thing to keep in mind is that air admittance valves come in various sizes, and you must match their size to your toilet. You should check your local plumbing codes and consider your toilet’s specifications before installing one. If you’re unsure about it, call a plumber.

Can you auto vent a toilet?

Toilets produce methane gas, among other noxious fumes, and for this reason, it is unsafe to use an in-line venting system. Most plumbing codes require toilets to be plumbed to connect to a vent stack, which conducts the fumes outside. The only exception is the air admittance valve if allowed by the codes in your area. Auto vents are not suitable for toilets.

Final Verdict

Venting a toilet without a vent is easy and cost-effective if you can install an air admittance valve. Otherwise, you’ll have to run a true vent or common vent through the walls and outside the house through the roof. Since venting a toilet is crucial for its proper functioning, we recommend calling a plumber if you’re not sure about the codes in your area or have any other doubts.

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