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How To Vent A Double Vanity [Step By Step Guide]

For many families, having a double vanity in the bathroom is a luxury because it allows more space to get ready in the morning. Bathroom vanities should be vented, and if you have a double vanity at home, you're probably looking at how to vent the sinks yourself.

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Luckily, we've done some research and have the answers for you!

Here are the steps to venting a double vanity:

  1. Check with your local building department to check which kind of drainage lines they allow in your area.
  2. Attach the double vanity sink according to the manufacturer's instructions.
  3. Cut the existing PVC pipe of the original vanity sink.
  4. Wrap Teflon tape on the copper drain pipe and attach an adaptor for the new pipes.
  5. Attach the PVC pipes and fittings properly before connecting them.
  6. Attach the mechanical vent to the new pipeline using the appropriate PVC pipes and fittings.
  7. Complete the installation of the faucets and water lines of the new sink.

Knowing the proper way to vent the sink in your bathroom's double vanity is very important.  In this post, we will share advice on why bathroom sinks should be vented and if there are alternatives if your current plumbing does not have a vent.

We also have a few suggestions on the best vents you can choose for your bathroom sink, so read on!

Luxurious bathroom with a grey double vanity with flowers sitting on the white quartz counter top, How To Vent A Double Vanity [Step By Step Guide]

How To Vent A Double Vanity [Step-By-Step Guide]

A double vanity is a luxury for many homeowners.

If you have the space to have two sinks sitting side-by-side in your bathroom, it will be easier to get ready in the mornings because it gives more room for grooming and flexibility to move about while preparing for the day.

Venting A Double Vanity Sink With Existing Vent Pipes

If you want to build a double vanity sink for your bathroom, there are two ways to go about it. Houses just being built can include this in the initial planning stages.

Your contractor or plumber will install vent pipes in the walls for the venting system. This will include everything that goes through the plumbing—sinks, toilets, baths, and even the washer.

Sometimes, bathroom vanities are built with only one sink in mind. As the years go by, some homeowners need to add another sink to their vanity.

If your bathroom already has one sink connected to the vent pipes, adding another sink to create a double vanity is as simple as installing a new set of drain pipes for the new sink.

Check out this video which explains adding a second sink to their bathroom vanity.

1. Check your local building codes

Young carpenter and mature quality control inspector building code

Before attempting to install a new sink to your bathroom vanity, make sure to double-check the local building codes of your area.

There are different plumbing requirements for other states and counties, so it's always important to check what you can and cannot add to your plumbing system.

If you are unsure about this particular process, seek the help of a professional plumber to help you with your sink installation.

These requirements are essential because they ensure your family's safety, and it might cost you more if you have to redo an entire project because of a missed requirement.

2. Attach the sink to the vanity

Installing a metal sink with an assembled white sewer pipe

This process will differ depending on the sink you purchased for your vanity. Most manufacturers will include an instruction sheet to help you install the new sink on your vanity.

You'll probably need to cut through the existing counter in your bathroom, or you'll have to purchase an entirely new countertop before starting this project.

If you wish to install the new bathroom sink and have it share a common drain line, the distance between the two sinks should only go to a maximum of 30 inches.

Any further than this will require the two sinks to have separate drainage lines in the bathroom.

3. Cut the existing pipeline

Using a hacksaw, cut off the existing drain pipes of the original bathroom sink. This is to provide a new line where the new sink and the old one will be joined together.

After cutting through the old PVC drain pipes, wrap the threaded adapter with Teflon tape. Thread a female adapter to the existing copper pipe, and we can begin fitting the new pipes.

A double vanity sink does not require separate P-traps to drain correctly. You can use a P-trap for one sink and a Y-trap to connect the other sink to the same drainage line.

These pipes should connect to the original pipeline where the existing pipe vents are already located.

4. Attach the new pipes

Prime and glue all the PVC pipes and pieces to install the two sink drain together. Measure the height of the pipe branch that will go through the vanity cabinet and mark the space where a hole should be drilled.

Using a drill with the appropriate sized drill bit, cut out a hole that will fit the new PVC pipe and its other fittings.

Attach the pipes and thread them through the cabinetry until it connects to the new sink. Check all the connections and see that no loose fittings are prone to leaks.

5. Install the faucet and water lines

Braided plumbing hoses are used to install faucet in bathroom

Install separate shut-off valves for the water lines to provide access to both sinks. These different shut-off valves will also help you service the two sinks separately when needed.

After fixing the water line, install the faucet according to the manufacturer's instructions. Seal all the spaces and areas before completing the sink installation.

Venting A Double Vanity Sink With No Vent Pipes

Another option for bathrooms that do not have access to a vent pipe is adding a mechanical vent to the drain pipe. Installing the PVC pipes is the same as all bathroom sinks, but a mechanical vent is also attached to the pipes.

This mechanical vent should be in the highest possible place in the cabinet under the sink.

This video will show you how to add a mechanical vent to an old sink. 

Do You Have To Vent A Sink?

Plumber working in the bathroom

The vents are one of the essential things in a bathroom plumbing system. To keep the wastewater flowing freely down the drain, the pipes should have vents to allow air to push the water downwards.

The home's entire plumbing system connects to the vent pipes during construction. Your plumber will ensure that the bathroom group plumbing (toilet, sink, and bath) has pipes connecting to a vent.

Other areas of the home that connect to the venting system would be sinks and drain in the kitchen and other areas that need pipe drains.

However, there are occasions when sinks do not have vents. This is often the case during remodeling, as additional venting cannot be added unless the entire house is renovated.

If this is the case for your home, there are other options to vent the sink without tearing down the walls.

To allow venting in bathroom sinks that are not connected to vent pipes, plumbers often use mechanical vents or air admittance valves.

These valves attach to the drain lines using an additional pipe and work with negative pressure to allow air to enter the pipes to keep the water flowing.

Best Air Admittance Valves For Bathroom Sinks

Several air admittance valves are available on the market for any plumbing system. They are relatively easy to install and quite affordable, which is a great option instead of breaking down the walls to install a vent pipe.

A well-known brand for plumbers, Oatey has created an air admittance valve that can be easily installed without a branch vent. This mechanical valve is sensitive to pressure changes and easily breaks the air vacuum in the pipes to allow water to flow.

Check out the Oatey air admittance valve on Amazon.

Another excellent option for a mechanical vent is the Studor Mini-vent. This mechanical vent works similarly to the Oatey but has a more compact design.

This mechanical vent is great to use in cabinets and under-sinks with limited space. The Studor Mini-vent is also ideal for an individual sink or a group of fixtures that share the same drain line.

Get the Studor Mini-vent on Amazon.

Wrapping Things Up

A contemporary modern bathroom design

A bathroom with double vanity is perfect for homes with a lot of space for people to get ready. While installing a new sink can be easy, homeowners often forget the requirements for their plumbing systems.

Don't forget to go through your plumbing requirements and vent them properly to make your bathroom fixtures last very long.

Made it to the end? Check out these helpful related articles below!

How Much Space Should There Be Between Toilet And Vanity?

Does A Double Sink Vanity Share The Same Drain?