Modern plumbing is a wonderful invention, and many of us take it for granted. When trying to understand the many working components, it’s easy to become overwhelmed or confused.
One of these working components is a vent, and as we’ll discuss later, some older homes do not have these vents installed. If you find yourself in this situation, what do you do?
An air admittance valve is an alternative to a toilet vent. This mechanical one-way valve works to move wastewater efficiently, is economical, and easy to install. An air admittance valve works by balancing the pressure in the drainage system.
Currently, an air admittance valve is the only alternative to a toilet vent. All other options require the installation of a vent pipe. Here, we will cover how an air admittance valve works, its advantages and disadvantages, and how to install this device.
What is a Vent, and Should You Vent a Toilet?
Due to the nature of a plumbing system, it is very important to vent a toilet. On its own, a drainage network is a closed system, meaning there are seals preventing the introduction of air or the release of sewage gasses.
Air pressure helps wastewater move efficiently into the sewage system, which every homeowner appreciates. No one wants backed up, poorly draining sewage in their home. Not only does this present offending smells, it poses a sanitation hazard that negates the whole purpose of modern plumbing.
Not only does a vent introduce air that helps wastewater drain quickly and thoroughly, it also removes sewage gasses that are problematic when trapped in the drain system. These sewage gasses can create bubbles that hinder the drainage of waste, and can come up through the toilet, carrying bad smells into the house.
Typically, vents are attached to plumbing systems in the form of thin pipes. These vents are connected to pipes that drain our toilets, sinks, and bathtubs, and go outside through a segment of the roof.
Vents introduce air from outside that allows wastewater to drain, and release sewer gasses outside through the roof. You can see this part of the vent coming out of the roof. It can be difficult to tell by sight whether the vent services your toilet, but there is a way to find out.
If you can safely get onto the roof, inspect the vent stack. See if there are any blockages caused by leaves and debris. Now have someone inside the house flush the toilet, and listen for running water through the vent stack. If you hear running water, it’s connected to your toilet.
It is common for toilets installed over 30 years ago to not have vents attached to their drainage pipes. You can consult a professional to make the appropriate adjustments, or install a vent alternative yourself. While a professional consultation may be a good starting point so you can learn about all of your options, a vent alternative is much more economical and less involved than installing a vent for your toilet.
What is an Alternative to a Vent?
If there isn’t a venting pipe installed for your toilet, or the one you have is damaged and not working correctly, there is an alternative that you can install. The component costs just $20, and requires few tools to install.
This affordable, easily installed alternative is commonly known as a studor vent, but the official name for this device is an air admittance valve. These aren’t technically vents, but rather valves that allow the inflow of air.
Air admittance valves are simple in design, but can make a big difference in the efficiency of your draining system. Like we mentioned before, air helps wastewater drain quickly and completely, reducing strain on the plumbing and ridding the house of unwanted waste.
While air admittance valves don’t do as much as a full vent system, they can be a great alternative to an expensive vent installation. To help you decide whether this alternative is right for you, we will cover how an air admittance valve works, its advantages and disadvantages, and how to install the device.
How Does an Air Admittance Valve Work?
This one-way mechanical valve is comparable to a vent in that it allows air to enter the drain pipe while preventing sewage gasses from coming up through the drain. Air admittance valves are not just for toilets, these small devices can be installed in sinks, or connected to the sewer system exposed in basements.
An air admittance valve is designed to sense changes in pressure in the drainage system, and react accordingly. So, when negative pressure in the toilet drain builds, the valve will open to allow air into the drain pipe. This air equalizes the pressure and helps flush the wastewater.
Once the pressure in the drain is equalized, the valve will automatically close an create an airtight seal. This airtight seal prevents sewer gasses from escaping through the toilet, which is a very unpleasant problem to deal with.
At first glance, it might seem that an air admittance valve is an obvious alternative to a vent system. Before making the decision to install this device, it is important to consider all aspects involved. While it certainly has its advantages, there are some disadvantages to consider. Here are some pros and cons of an air admittance valve.
| Pros | Cons |
| Far less expensive than a vent | Traps sewage gasses in the drainage system |
| It doesn’t damage the roof | Prohibited by some state and city building codes |
| Easy to install |
How Do I Install an Air Admittance Valve?
With just a couple of tools and a few supplies, you can easily install an air admittance valve in an afternoon. As with all projects, though, there is a bit of planning involved. Before you get started, make sure you have these on hand:
- A segment of pvc pipe (if you need to install an extension to bring the valve to the appropriate height)
- Tape measure
- Pipe Cutter
- Metal File
- PVC sealant
- Teflon tape
Once you have your tools and supplies ready, you can start to plan the location and installation of your new air admittance valve. Make sure to plan carefully, otherwise you risk wasting time and possibly making unnecessary cuts to vital drainage pipe.
Remember, it never hurts to consult a professional plumber if you have any doubts or questions about this process and whether it is appropriate for your plumbing system. They can evaluate your system to determine the correct course of action, and make recommendations of which air admittance valve to install.
Step 1: Make Sure You Have the Right Air Admittance Valve
There are different sizes of air admittance valves available to service different fixtures. It’s important to know the Drainage Fixture Unit (DFU) load of the fixture you intend to address. When choosing an air admittance valve, remember that household toilets have a DFU load of 3, and if you intend to address all of the bathroom fixtures (sink, toilet, bath) you’ll need a valve with a DFU load of 6.
It is very important to select the right size air admittance valve. If you select a valve that is too small, it won’t be able to service the fixture efficiently. Also, you will have wasted time and money installing the incorrect device.
Step 2: Locate and Measure the Install Location For the Valve
Keep in mind that the air admittance valve will need to be installed in an area that is accessible. There also needs to be a decent amount of airflow to the device-it will need to pull air from the atmosphere in order to work correctly.
Be sure to plan the position of the new valve to avoid unpleasant surprises. To operate safely and correctly, the air admittance valve needs to be installed at least 4” above the horizontal branch of the drain, and at least 6” away from any insulation material.
Now measure the pipe where you intend to install the air admittance valve. Generally, the air admittance valve should be half the size of the pipe it’s serving, so bear this in mind. Also, there are adapters available in different sizes to accommodate all drainage pipes. Before you get started, make sure there is enough room for the valve and the adapter.
Step 3: Turn the Water Off
Now that you have everything planned out, you can get started with the installation. Begin by turning off the water supply to the toilet. Locate the water line that supplies the toilet and cut off the water by turning the knob on the water line. The water line can be in the flooring or coming from the wall.
Now flush the toilet to remove all of the water from the bowl and the tank. To be on the safe side, you can put a receptacle or towel under your work area to catch any water that didn’t drain.
Step 4: Cut the Pipe Accordingly
This depends on where you are placing the air admittance valve, and whether you need to install an extension to bring the valve to the recommended height.
With your measuring tape and a marker, mark where you need to cut the pipe. Use a pipe cutter to cut the pipe at these marks.
Step 5: Chamfer the Pipe
This seems like an extra step, but it is very important to chamfer the pipe. During this process you’ll get rid of sharp edges that will push pvc glue or cement away from the point of contact. You want a good seal, or you’ll risk air leakage that will defeat the purpose of your new valve.
This can be easily done with a metal file. Simply file away the sharp edges of the pvc, and you’re done!
Step 6: Adhere the Adapter to the Pipe
With pvc glue, attach the adapter to the pipe. Make sure to coat all points of contact with a 1-½ to 2” band of glue. It can take up to 2 hours for pvc glue to completely dry and bond the pvc, so now is a good time for a break.
Step 7: Install Air Admittance Valve
Wrap Teflon tape around the threads of the air admittance valve to ensure an airtight seal, and screw air admittance valve into the adapter.
Step 8: Turn the Water On the Test the Air Admittance Valve
Now you’re ready to test your new valve! Using the knob on the water line, reestablish the water supply to the toilet. Once the tank and toilet bowl are filled, do a couple of test flushes. You should feel suction from the air admittance valve, indicating that it’s pulling air into the drainage system.
When Should You Call a Professional?
It’s never a bad idea to consult a professional plumber when making any changes to your current system. This is especially important when you have an older system. You don’t want to risk any expensive damage to your system by introducing a device that is incompatible.
If you have several toilets to vent, it may be a good idea to consult a professional, as this is a big project. After an evaluation of your current system, it may be decided that a vent installation is a better course of action, or even a complete plumbing update. These are big projects that are best completed by professionals.
The cost of hiring a professional depends entirely on the work they end up completing. In this scenario, a professional plumber is likely to install a vent for your plumbing system. The average cost for this repair is $500, which of course varies with the amount of work required for installation.
While this is certainly more expensive than a $20 air admittance valve, it is sometimes the better option for your house. It is very important to evaluate your needs and your current system carefully to determine which course of action is best for you.
Ruben has a diverse background in the home services industry, with experience running a construction company, a kitchen and bath showroom, and a moving and relocation company. This breadth of experience has provided him with a wealth of knowledge and expertise in various areas of home improvement in general and specifically in the heating and plumbing niche.