How To Vent a Kitchen Sink Under a Window: 8 Easy Steps


Venting your sink properly is crucial to it functioning well. But, if you’re installing it under a window, running the vent pipe can prove a challenge. 

The simplest way to vent a kitchen sink under a window is running the vent pipe horizontally under the window, until it connects with the main pipe. However, your pipe should always slope upwards. In most cases, your vent installation will take a few hours of work at most. 

How to Install a Vent Pipe Under a Kitchen Window

While installing a vent pipe under a kitchen window might sound complicated at first, it’s relatively simple. In fact, it’s a basic matter of simple math, knowing where your main vent shaft is, and drilling holes in your walls. 

If that fits inside your technical skills, feel free to proceed with installing your own kitchen vent pipe. 

1. Gather materials 

You’ll always need basic materials to get started. 

  • Tape measure 
  • Pencil or chalk line 
  • Level 

You’ll also need additional supplies to install the kitchen vent pipe, but you can acquire these after measuring things. 

  • Drill with 1 5/8’ths Forstner bit or a spade or paddle bit of the same size. In this case, we’d recommend the spade or paddle bit, because it’s easier to use with a hand-held drill and easier to drill precise holes without 
  • Phillips’s screwdriver and drill bit (for removing baseboard) 
  • Hammer (for removing your baseboard) 
  • 1 ½’ PVC or ABS plastic pipe (try to match what is in your home already) in your home 
  • PVC or ABS sanitary tee (2’x2’ and 1’ x ½’)
  • Long-sweep PVC or ABS pipe elbows (1’ x ½’) 
  • PVC or ABC connectors 
  • PVC or ABS pipe cement to match the pipes you bought 
  • Chalk line or cord and nails 
  • Y-connector in ABS or PVC 

If you don’t already have a P-trap in your sink, now is the time to install one. However, it’s important to remember that your local jurisdiction may not allow you to do so yourself. Always check local plumbing regulation before adjusting your plumbing. 

2. Measure the distance to the main vent

Your home likely has a main vent. This might vent in the attic. It might also vent into a wall. In most places, the main vent is conveniently close to the kitchen. That won’t be the case if you’ve moved your kitchen. However, the vent almost always vents into the roof. This means you can assess blueprints, check vents in the attic, or just check the roof if you’re not sure where it is. 

Your sanitary tee may be a maximum of 3.5 feet from the P-Trap. You can measure to this distance or shorter for the starting point of your vent pipe. In most cases, you’ll want the sanitary T closer to the sink, but where it’s still relatively easy to direct the pipe under the window. 

Once located, measure the distance between your P-trap and the main vent. Write that down and consider double checking the measurement. 

3. Opening up the wall 

Pipe vents are always installed inside the wall, under the window. This means you’ll have to remove the baseboard or wood between the sink and the main vent. With some luck, you’re installing your vent pipe before this goes on and before your cabinets are put into place. If not, you’ll have to move them. 

4. Chart your upwards trajectory 

The International Residential Code, which is law in 49 states, mandates that your sink vent must rise at least ¼ inch per foot. This means that if your sink is located 12 feet away from the main event, the pipe must rise at least 3 inches between the first connection and the last. This is to ensure that adequate pressure exists and that gasses from the sewer are encouraged to rise through the pipes. 

Most installers use a rule of thumb of a 45-degree angle for their vent pipes. You also want to maintain this angle until the vent pipe is 6” or higher above the highest fixture on the floor. 

In addition, you can measure this upward slope from the floor. You can also use a digital level, angle measure, or a level to chart the angle. A simple torpedo level costs from $5-$20 at most hardware stores and has rise marked out per 1/8th inch. 

Use a chalk line or twine to mark the full trajectory of the vent pipe’s rise. Measure that length. 

Finally, it is possible to take your vent pipe around small corners. However, this is not always a good idea. Corners slow airflow and could result in your sink backing up. In this case, you may want to consult a professional plumber for advice before moving forward. 

5. Purchase PVC Pipe and Glue 

Purchase PVC pipes and glue to cover the distance measured above. If you haven’t worked with pipes before or aren’t certain of your measurement skills, consider buying 20% more than you need. 

You need 1 ½ inch PVC or ABS pipe with corners, a long-sweep elbow, and a fitting to connect it to the main vent. You’ll also need a Y fitting to tie the vent into the main vent. Double check that your main vent is 1 ½ inches before making this purchase. 

6. Drill holes 

The first step to installing your pipe vent is to drill holes along the chalked line. Here, you may want to avoid drilling holes altogether. Some people prefer to install pipes inside their cabinets to avoid the risk of structurally damaging their walls. In addition, some local regulations require you to inspect the home before drilling holes in beams. 

As a general rule, you want to avoid drilling holes in primary support beams if you can help it. In addition, you want to center holes inside the wall. If you notch a beam, you create a weak spot on one side, which could result in structural collapse. 

The 2012 International Residential Code book lists standards on page 159 and 160. According to the code book, you can safely drill into load bearing wall studs providing the diameter of the hole is less than 40% of the total stud size. If the diameter of the hole is 40% or more of the width, you have to double the stud (by placing a second 2”x4” or 2”x6” alongside it in order to complete the changes safely. 

Drill your holes in a straight line following the upwards slant. Make sure every hole lines up. In addition, you have to ensure that pipes do not bend too much or snag too much in the holes. For this reason, you should use a 1 5/8ths” paddle bit for the holes. 

7. Install your vent 

Most people prefer to connect their pipes and to ensure that the cuts are good before gluing. This allows you to take apart and reconnect everything in case you make a mistake. 

  1. Install the sanitary tee. Fit the 2”x2” side of the sanitary tee into the P-trap. Make sure that it is no further than 3.5’ from the bottom of the P-trap. Make sure the 1 ½ port is facing upwards
  2. Cut and attach 1-2″ of pipe 
  3. Attach a long-sweep elbow to the pipe, facing it directly to the wall 
  4. Connect a longer run of PVC pipe and push it through the holes
  5. Add joints as necessary to reach your destination 
  6. When the full pipe is at least 6” above every other outlet (e.g., if you have an attic sink, it must be at least 6” above that”) in the house, you may connect the vent pipe to the main vent 
  7. Use your Y-connector to join the two pipes. To do so, cut the main vent, install the Y with the Y facing down, and attach the two other pipes. 

8. Allow the glue to dry 

Double check that everything is where you want it, glue it, and allow the glue to dry. In most cases, PVC and ABS cement wants at least 24 hours to dry. You should wait to put drywall back on until after this period. 

Why Place Your Kitchen Sink Under a Window

Kitchen sinks are traditionally installed under windows. But, other than having a possible view while washing up? Actually, yes, there are plenty of good reasons to install your kitchen sink directly under a window.

Maximizing Wall-Space 

Kitchen sinks are a great place to use a space that can’t actually fit a refrigerator, a wall unit, or overhead cabinets. Windows limit what you can place in that space. Therefore, a kitchen sink, which usually perfectly fills the space, is a great way to go.

However, that’s not the case if you’d like to have cabinets over your sink. For example, if you want to hang your drying rack. Or, if you want to store dishes directly over the sink.

Good Natural Light

Windows allow you to utilize daylight when washing up. That means reducing daytime electric usage. It also means you can enjoy sunshine or the view in your yard while washing up. That might be a nice way to wake up. Historically, one of the reasons sinks are placed under windows is also children. If your window overlooks your yard, you can more easily keep an eye on kids from a central point in the kitchen.

Drainage Locations are Often near Outer Walls

Drainage and central vent locations are most often attached to the outer walls. Most homes have central vent pipes that exit through the roof, usually along an outer wall. This means it’s cheaper to install a kitchen sink along an outer wall, because you’ll have less distance to cover to reach the central vent.

Minimizing Kitchen Installation Costs 

If you’re installing a full new kitchen, you want as many appliances as possible along one wall. And, that often means the outer wall. Why? It’s a lot cheaper and faster to run hot and cold-water lines in a straight line, around a single wall. The same holds true for plumbing. Plus, that remains true whether you’re installing the sink vent or a connection to the sewers.

Ventilation 

Dishes can smell. Especially if you don’t wash them on the same day. Having a window over the sink gives you the option to simply open the window and air everything out.

Easy Access to the Sink 

Windows tend to be centrally located in kitchens. This means that installing your kitchen sink under the window puts it in a central, highly accessible location. While this won’t be the case in every kitchen, it is very often so.

Frequently Asked Questions

Venting a kitchen sink is relatively easy, providing you can easily take your baseboard off. However, you might still have questions. Hopefully, this FAQ will help. 

How high should a window be above a kitchen sink? 

Kitchen windows are traditionally set at 37 inches above the kitchen floor. This gives the window some clearance over the kitchen counter, which is traditionally 34 ½ inches + the countertop height of 1 ½ inches. 

However, this is purely tradition. You can set your window wherever you’d like behind the counter. However, you cannot easily have a window that is lower than the kitchen sink, because the plumbing will be visible from outside. 

What size window should be over a kitchen sink? 

Most people prefer to have a kitchen window that looks good with their kitchen cabinets and their sink. This means that you may want to choose a window based on your other furnishings. For example, if your cabinets are 36” wide, you may want a window in a similar size. In most cases, cabinets are 34” tall before you add the countertop. Kitchen sinks also average at 30-33 inches wide for a standard double sink. So, 30-40 inches wide and 30-40 inches tall will balance with your other furniture. 

At the same time, you may prefer a smaller or a larger window. Choose what works for your preferences, budget, and home. 

Next Steps 

Installing a kitchen sink vent is an essential part of plumbing. In fact, it does more than prevent your kitchen from smelling. It also prevents air pressure from clogging your drain. And, now you know how to install one under a kitchen sink.

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