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How To Vent a Toilet Without a Vent

Updated
No vent? No problem. Use an air admittance valve to vent your toilet.

Don’t panic if your toilet vent is blocked or you don’t have one. Getting rid of bad odors needn’t require a major construction project. It can be done a lot cheaper and easier than you might think.

We show you how to vent a toilet without a vent, talking you through the process in a step-by-step guide, giving you hints and tips along the way.

How to Vent a Toilet Without a Vent

It’s a myth that all toilets require an outside vent. Cutting a hole in your roof to install a vent is messy, expensive, and complicated. Air admittance valves are a cheaper and more convenient alternative. They allow the air to flow into your drainage system without letting any odors leak back into your home.


Does Every Toilet Need a Vent Pipe?

You don’t need a vent pipe for every toilet. You can install an air admittance valve anywhere to vent the toilet. These valves are commonly known as cheater vents.

You should check with your local plumbing authority before installing one, as they are a bit of a gray area in America. Cheater vents are common in Europe, but the US has a patchy record of using these vents. They are less common, with most homeowners and professionals opting for an outside vent, typically through the roof.

How To Vent a Toilet Without a Vent

We’ve talked about air admittance valves and that you can install them anywhere, so let’s take a more detailed look at them and discuss what they are and what they do.

Air Admittance Valve

Air admittance valves let air into your drainage system to vent the toilet and prevent foul odors from leaking back inside your home. When the atmospheric pressure drops in the drainage system, the valve seal opens automatically to allow air to balance the pressure in the pipes.

When the pressure balance is restored, the valve closes to prevent odors from leaking into the house.

They come in all shapes and sizes, with the design differing between manufacturers and capacity. They are typically constructed from plastic with a mesh screen to prevent unwanted critters from crawling out of the sewer and into your home.

You can get the correct size valve for your home by determining how much waste fluid your toilet system releases per second. If you have a lower capacity, you could install a mini valve that handles 119 US gallons per minute.

For heavy usage, a maxi valve tackles 507 US gallons per minute. These cheater vents also withstand extreme temperatures from minus 4 degrees Fahrenheit to plus 140 degrees Fahrenheit.

What You Need

Before starting your project, make sure you get the right tools and materials. The good news is that installing an air admittance valve is relatively easy if you have some basic plumbing skills.

  • PVC saw or backsaw.
  • Miter saw.
  • Deburring tool.
  • Marker pen.
  • Pipe cement.
  • Air admittance valve.
  • Spare drain pipe.

1. Locate the Drain Pipe

Find the main drain pipe in the floor beneath the toilet and trace it along until you find the 4-inch main drain line pipe. This may involve you lifting floor coverings and floorboards.

2. Saw the Pipe

Grab the marker pen and draw where you intend to cut. Use the PVC saw and cut through the drain line about 4 inches before the pipe connects to the drain stack. Consult your local plumbing codes to determine how far to locate the vent from the toilet.

The tee pipe doesn’t need to be vertical. If you lack the space, grab the miter saw to cut an angle no more than 15 degrees in the required direction.

Use the deburring tool to neaten the edges of the cuts and holes so that the pipes get a snug fit.

3. Install the Tee Pipe

Install a tee fitting at your cut by sliding the two cut ends of the pipe into the opposite ends of the fitting. Push the cheater vent onto the other inlet on the fitting. You can make adjustments by twisting it left or right. This stops any interference or obstructions caused by the valve.

4. Glue It In Place

Once you are satisfied that they fit correctly and the positioning of the valve works, remove the fittings and vent. Now coat each end of the pipes and the vent with pipe cement. Reassemble the fittings in the same configuration as beforehand and let the adhesive dry for a couple of hours.

You could use glue if you don’t have pipe cement to hand. Spray adhesive is very effective and dries quickly, which means you can get the job done faster.

FAQs

What Happens if a Toilet Is Not Vented?

If your toilet is insufficiently vented, it could cause issues moving wastewater and solid waste away from your home. This leads to backed-up pipework, blocked drains, and foul odors seeping back into your property.

One of the most prominent signs you lack the correct ventilation is sewer gasses escaping into your home.

Can a Toilet and Sink Share a Vent?

You can vent a toilet and a sink on the same air admittance valve. You shouldn’t exceed more than two fixtures as the vent will struggle to cope.

To share the same vent, the toilet drain should be 3 inches in diameter and the sink drain no smaller than 1.5 inches.

Can You Vent a Toilet Out the Wall?

While it is more common to have a stack running through the attic space and vented out of the roof, you can vent a toilet through a wall, but there are conditions if you opt to do it this way.

You should consult your local plumbing codes, but as a general rule, the vent must rise vertically past the top frame of the highest window in the house. In some instances, the vent pipe should extend above the roofline, which defeats the objective of saving time, effort, and money trying to avoid fitting a roof vent.

Extending the vent out of the wall has disadvantages because where the pipe extends vertically, the bend is prone to blockages. Also, cleaning the vent is more challenging. Plus, plastic pipes are susceptible to extreme weather conditions, causing them to freeze, crack and become blocked.

Can You Vent a Toilet With a 2-Inch Pipe?

You can vent a toilet using a 2-inch pipe. Some plumbing codes prefer 3 or 4-inch tubes, and the distance that the line needs to extend has an impact on the diameter. Some vent channels can be as small as 1.25 inches in diameter.

The best advice is to use 3 or 4-inch diameter pipes because they move air more easily and are less likely to get blocked.

Can a Toilet Vent Run Horizontal?

The key to a vent pipe is it must stay dry. So, if you are venting horizontally, you need to ensure that the line stays clear of blockages, and if any water gets into the vent, it can run into the sewer.

You are limited to the distance you can run a horizontal vent pipe, with some placing the maximum length at 8 feet.

The answer is to run the pipe along a gradient, so while it is horizontal, the water still flows downhill towards the sewer without creating a trap.

Does a Vent Stack Have To Go Straight Up?

It all comes down to the question of keeping the vent dry. Vertical pipes are better because there is nowhere for the moisture to linger. It flows away, leaving the vent clear of traps. However, many wall vents have a 90-degree bend to allow the vent pipe to extend above the roofline.

If debris falls into the pipe, the bend is the weak point where blockages collect. If that happens, water becomes trapped, and the vent no longer fits the purpose. It’s also more difficult to clear because the angle inhibits a plumber’s rod.


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About the Author

Mark Weir

Mark spent 24 years working in real estate, so he knows his way around a home. He also worked with contractors and experts, advising them on issues of planning, investments, and renovations. Mark is no stranger to hands-on experience, having renovated his own home and many properties for resale. He likes nothing better than seeing a project through to completion.