Informational Guide

How To Vent A Kitchen Sink Under A Window

Wondering how to vent a kitchen sink under a window? It’s not that difficult when you know how. Just follow our easy step-by-step guide.

by Ian Haynes

Plumbing codes require all fixtures to be adequately ventilated to work correctly and protect your health. Even the best sinks are useless without proper ventilation, but thankfully there are a lot of different methods available.

In this guide, we'll explain how to vent a kitchen sink using a window and the benefits it can bring.  

A vent is literally just a pipe that is used to direct air from your plumbing and out of your home. They will usually rise to your roof and vent out there where no harm can be done to anyone. The primary purpose of this ventilation is to control the air pressure in your plumbing system.  

Plumbing systems use gravity to direct water down into the sewers. To avoid water flowing at a very high speed, various traps are built into your plumbing to make it curve and slow down.

They also function to stop harmful sewage gases from rising back up into your home.  

Kitchen Sink Drain

These traps only work if there is a bit of residual water in there, but if there is an excess of air pressure, then the suction will take too much water out of your system. This allows harmful gases to escape back into your home. Having the right pressure in your pipes is essential for your whole plumbing system, and that's why ventilation is part of plumbing codes that have to be followed. 

Your kitchen sink vent line will sit underneath your P-trap and should connect up to your main vent stack. A main vent stack will run through your home behind the walls and run straight up vertically to your roof. However, many people have a kitchen window above their sink which means your vent can't run vertically.  

To solve this issue, you have to run it horizontally until it gets past the window and then turn it vertically, so it reaches the roof. More information on that later on in this article.  


Why Put Your Kitchen Sink Under The Window? 

There’s no denying that fitting your kitchen sink under the window makes it a lot more difficult. It’s more of a challenge to plumb your kitchen sink and more of a challenge to vent it, so why do people do it?

There are actually many benefits to having your sink there, which is why most kitchen sinks have a window right in front of them.   

1. The View 

Your kitchen sink is one of the most used fixtures in your home, and you will spend hours each week cleaning or preparing food there. If you're doing something mundane like cleaning the dishes, then it's much easier if you have a great view to look out. This makes it the perfect place to have a window.   

2. Natural Light 

Kitchens are very busy workspaces where you'll do a lot of delicate work. You need adequate access to light, and having a large window above the kitchen sink will give you a lot of natural light. This not only makes the work easier, but it also helps make the room much nicer to be in.  

3. Efficient Use Of Cabinet Space 

Kitchen sinks typically have two cabinets underneath them. These will house your plumbing but will also give you plenty of space to store other bits and pieces. This helps counteract the storage space you lose with the window and help make more efficient use of your kitchen.  

Kitchen Sink Under Window

4. Interior Aesthetics 

One of the main reasons people opt for a window above their kitchen sink is for aesthetics. There's no denying that it just looks so much better having a big window to help break up the busy workspace and give you some natural light.  

5. Breeze/Wind

Your kitchen will get hot, and there'll be a lot of different smells, some good, some bad. Having a window above your kitchen sink which you can open will help to provide some much-needed ventilation and stop you from getting so hot that you have to get out of the kitchen. It will also help stop any smell building up from dirty dishes around the sink.  


How To Vent A Kitchen Sink Under A Window Properly  

Venting a kitchen sink under a window is slightly more complicated than traditional venting because you have to avoid the obstacle. Your vent should join a central stack which will eventually rise to the roof of your building, but if there's a window above, then you'll need to run the ventilation lines horizontally before they go vertical.  

Before you get started on this work, you should make sure you have: 

Here’s a step-by-step guide to doing this yourself:  

  • 1
    Start by turning off the water supply so you can work freely. As you're dealing with the drain line, this isn't technically essential, but it's worth doing just in case.  
  • 2
    You’ll then need to install a tee in the drain line of the sink (this is usually found within the wall cavity). You should ensure this is installed no further than 3 feet from the bottom of the P-trap, or it won't be effective. Glue this sanitary tee to the pipe coming from the sink and then glue it to the other side, where it continues to the drain line. There should be two ports, so make sure the 2-inch one is connected to the drain, and the 1.5-inch port is pointing outwards.  
  • 3
    Use your hacksaw to cut a 2-inch length of the PVC pipe and attach it to the sanitary tee port. Then attach an elbow pipe that is parallel to the wall. This is where the ventilation will be directed to so it can pass beyond the kitchen window.  
  • 4
    Measure and mark a point comfortably past the kitchen window where the vent can safely turn vertical. Mark this out using chalk, making sure there's an upward slope of at least ¼ inch per foot.  
  • 5
    Use a drill and make holes in the stud along the marked-out route for the pipe. Make sure this is thick enough to accommodate the pipe.  
  • 6
    Cut the PVC pipe to the appropriate length and slide it through the studs, gluing it in place against the elbow fitted in step 3.  
  • 7
    Drill a final hole in the top plate of the wall and extend your vent, so it goes upwards. This should connect to your main vent stack and connect it using a reducing sanitary tee fitting.  

If your prefer that a professional does the job, then fill in the free form below for a local plumber in your area!


People also Ask (FAQs)

Does every sink drain need a vent? 

Yes, without a vent your drain won’t work effectively because there will be an imbalance of air pressure. This can cause harmful sewage gases to enter your home.  

How far can the vent be from the kitchen sink? 

Your vent should be no more than 2 ½ feet from the trap underneath the sink. If it's further away from that, it won't be effective, and your sink won’t work properly.  

Can two sinks share a vent? 

Two sinks can share a vent, but only if they have the same flood level rims. This basically means that your sinks need to be the same height to share a vent.  

How do I know if my kitchen sink is vented? 

The easiest way to check if your sink is vented is to run a lot of water down the drain. If your kitchen sink drain starts to gurgle, bubble, or even pop, then it means there is something wrong with the air pressure and it hasn't been adequately vented.  

Why is water coming out of my sink vent? 

An air gap is used in your drains to stop any water from flowing out of it. Over time, grease and other food debris can block this air gap, and that can lead to water flowing from your sink vent. This is usually simple enough to solve by cleaning the air gap in your kitchen sink.  


Conclusion

kitchen sink works really well underneath a window, but it can make the plumbing a bit trickier. Your sink needs a vent, and the window makes it a little more complicated, but it's still totally manageable. 

Hopefully, this article has helped you understand what you need to do and has given you the confidence to do it yourself. Remember, ventilation is essential for your whole plumbing system, so don't be afraid to get a professional involved if you need to.  

Ian Haynes is an expert writer who has successfully deployed over 500 plumbing pages and other related content. He has an excellent understanding of home plumbing issues and translates his experiences via Plumbing Lab so readers can have a better understanding of common household problems. Outside of his work, Ian likes exploring Brooklyn with his Labrador.

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