How to Vent a Kitchen Sink Under a Window


A kitchen sink vent is an air opening, typically round or rectangular in shape, vented outdoors. This is typically done by removing a window or cutting one into the wall. The purpose of this venting is to allow air pressure equalization between the indoor and outdoor environment. It also aids in preventing back-flow of sewer gasses if your home has a drain that runs directly from under your sink up through your plumbing drain pipe (see diagram). If there was no vent for this drain, all those nasty sewer gases could get pushed back up into your kitchen when you run water down that drain! Today I will discuss a technique on how to vent a kitchen sink under a window.

How to Vent a Kitchen Sink Under a Window

Does Kitchen Sink Need to be Vented?

There is a debate on whether to vent or not for kitchen sink installations. Most likely, you have been venting about this type of plumbing fixture and never really questioned its necessity. However, some plumbers will insist that it does not need to be vented at all, and more so, it is better if it remains non-vented because it is an open system.

For all practical purposes, a kitchen sink can be considered an open system. Its outlet is not connected to the sewer, and it is vented through the window instead. When you have installed the window correctly following the building codes and safety regulations for ventilation, everything should work fine.

However, some people will insist that this fixture should always remain vent-free because of its proximity to the food preparation area. They claim that odors or airborne bacteria from sink waste can contaminate your food, especially when it comes into contact with water.

Step-wise guide on How to Vent a Kitchen Sink Under a Window

Step 1: Installing a Sanitary Tee:

A sanitary tee is a fitting that allows you to take two pipelines and comingle them into one. I use this under the sink to join the waste from the kitchen with the disposal pipe (which will be outlined later). Find a horizontal surface in your kitchen like a cabinet top or countertop; make sure it is level by screwing in some screws at various locations on the top of it.

Step 2: Get Your Materials Ready :

To vent your sink, you are going to need four things.

  • A 3-inch diameter PVC 90-degree elbow joint
  • One PVC 4-inch diameter ell which can fit onto your current pipes. For instance, if your sink has 1½ inch diameter lines coming out of it, then your joining PVC pipe will be 1½ inches in diameter. Keep this measurement in mind as you are shopping for the ell.
  • Pipe Collar, This is a 3-inch 90-degree pipe joint that will go on top of the elbow that comes off from your sink. The reason it’s 3 inches long because it needs to extend past where the window sill starts so that you have something to mount against. These can also usually be found at Home Depot or Lowes.

Step 3: Begin Attaching Your Components:

First, take your ell and attach it to the side of your sink. This is easy since a male threaded pipe will screw right into another one.

Next, take the PVC elbow joint and screw it onto the other end of your ell. This is also fundamental plumbing. Make sure you get tight-fitting joints as you don’t want any leaks!

Attaching Pvc Pipe

Step 4: Attaching The Pipes To The New Joint:

Now that all your hard work has been done; time for some more basic plumbing! Take a 1½ inch diameter pipe and cut it so that about 8 inches is left attached to the kitchen sink (you will be throwing this down the garbage disposal later). Using Teflon tape or epoxy putty, connect this 1½ inch diameter pipe to the bottom of your ell-to-sink joint. Then run it out through a window and down the side of your house (or wherever you want it to go). You can then secure this pipe with brackets against the side of your house.

Step 5: Finishing Up:

Now that all of your pipes are securely fastened together with high-quality connections, we are almost done! The only thing left is making sure there isn’t any vacuum created in our system by having air get sucked back into our sink when we turn off the water. To combat this, we add a trap arm which consists of another ell and a pipe collar.

The trap arm connects to the newell and then goes straight down to the floor (or baseboards if you are on a raised level), where it gets connected to your main waste line with some more elbow joints to prevent air from coming back into your sink when you turn off the water supply line.

Step 6: Bask in Your Accomplishment:

You can now bask in the fact that you have successfully vented your kitchen sink under a window! Don’t forget, though, for safety reasons, any time you do any kind of plumbing, make sure everything is dry first! This means that before installing an ell joint or PVC pipe, you should always check to see if everything is dry first. If you have any doubts, then wait! The last thing that we want is for someone to slip and fall because the water was on the floor.

Installing Kitchen Sink

Precautions While Performing How to Vent a Kitchen Sink Under a Window

  • Ensure the replacement window is as energy efficient as the original one
  • Venting a kitchen sink under a window requires deep excavation with heavy power tools and equipment working close to windows and doors, leading to serious injuries if not handled properly. Hence you must hire a professional to do this job for you.
  • Always wear protective gear like steel-toed boots, goggles, and dust masks while venting your kitchen sink to protect yourself from accidental injury or breathing in the dust particles generated by the work being done
  • Read any disclaimer form before taking up this project seriously, as it contains all the warnings you need to know about venting a kitchen sink under a window
  • Venting a kitchen sink under a window is not the work of an amateur. It is only suitable for those who actually know what they are doing
  • Work with a professional to get your kitchen sink vented properly and safely as venting a kitchen sink requires deep excavation with heavy power tools working in proximity to windows and doors and, if not handled correctly, may lead to serious injuries
  • Ensure that you clear out all unnecessary items from around your kitchen sink before venting so that you have easy access to the walls behind which plumbing lines lie to avoid any risk while working close to them

What is an Air Admittance Valve?

Air Admittance Valve

An air admittance valve (AAV) is a device used to connect outside and inside plumbing while helping to meet tight energy code requirements for building ventilation systems. An AAV directs a small amount of the sewer or septic waste-water flow to the outdoors without allowing odors into the home. They use pressurized air, which ventilates the drain line of built-up odor gasses and methane gas.

AAVs can be installed in new construction, on replacement drains, and on remodels too. The majority of AAVs are installed just below the window level beneath a kitchen sink or vanity. This location allows for easy access by city inspectors during government-mandated inspections before occupancy permits are issued.

An AAV is installed above a P-trap in the drain line and must flow into an accessible DWV pipe. Because it can be expensive to repipe, many homeowners choose to install AAVs on existing drains when remodeling or updating kitchens and bathrooms.

If installing an AAV in new construction, one should make sure that the trap beneath the sink passes code because a 1 1/2″ air admittance valve requires a 2″ by 2″ trap with at least 2 inches of water in it to work properly. One may opt for a larger trap if there is the adequate room because this will ensure a more reliable operation of your plumbing system.

They can be installed in new construction or on a remodel. They are easy to find at plumbing supply stores and online. However, you must order a high-quality AAV because using cheap plastic valves will lead to leaks and problems, which could cause your septic system to fail.


Once everything is done, turn your sink on and off a few times and listen carefully for any leaks. This can be tough since there aren’t likely any leaks at this point, but try your best to determine if there are any by using a flashlight or something similar.

And that’s it! You’ve successfully vented your kitchen sink under a window without needing to drill through a load-bearing wall/beam or run pipes out the side of your house! Good job! I hope you have learned the process of how to vent a kitchen sink under a window from this article. Thank you and have a nice day!

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