How to Install a Vent Pipe for a Kitchen Sink That Is Under a Window

Glenda Taylor

Washing dishes, peeling potatoes and scrubbing vegetables aren’t the most exciting tasks, which may be one of the reasons many homeowners opt for a window directly above the kitchen sink. During sink installation, the plumber makes provisions for a drain and ventilation system that allows water and sink disposal waste to drain efficiently to the main sewer line. While drain pipes run downward, vent pipes run upward. Since the kitchen window placement blocks vertical venting, an alternative venting route is necessary.

Adequate sink ventilation reduces clogs.

Step 1

Attach a 2-by-2-by-1.5-inch PVC sanitary T-fitting to connect the horizontal sink drain pipe to the 2-inch waste drain pipe from the sink. This connection is located in the stud space in the wall directly behind the sink. This fitting has three openings. The 2-inch side opening connects to the sink pipe and the other 2-inch opening faces downward. The 1.5-inch opening faces up. When you install PVC pipes and fittings, use PVC primer and PVC adhesive as instructed on their respective containers.

Step 2

Decide the configuration of the vent pipe. From the top of the sanitary T-fitting, the vent pipe must extend upward a short distance, then turn and extend horizontally through the wall studs until it reaches a stud space where it can ascend vertically again.

Step 3

Cut a short vertical piece of 1 1/2-inch PVC pipe with the pipe saw and connect it to the opening in the top of the sanitary T-fitting using the PVC primer and adhesive. The length of this piece depends on the distance and slope of the horizontal pipe, but in general, it should be about 2 inches long.

Step 4

Snap a chalk line on the sides of the wall studs to represent the horizontal vent pipe length and slope. The horizontal pipe should slope upward at the rate of 1/4-inch per foot. For example, if it’s 4 feet from the elbow connection to the stud space where the vent pipe will turn upward, the second turn must be 1 inch higher than the elbow connection.

Step 5

Fit a drill with a 1 3/4-inch hole bit and use the chalk line as a rough guide to drill a hole through the middle of each wall stud to run the horizontal vent pipe.

Step 6

Insert the horizontal pipe through the holes and connect it to the elbow fitting. Attach a second elbow fitting at the end of the pipe, with the opening facing upward.

Step 7

Install a vertical PVC vent pipe straight up until you reach the attic. You will have to drill through the ceiling plates to get the pipe through.

Step 8

Attach another PVC elbow to the top of the vent pipe in the attic, and run the pipe horizontally, with the correct slope, to meet the house’s main vent-and-soil stack, which is either 3 or 4 inches in diameter, depending on local codes.

Step 9

Connect the vent pipe to the stack, using a PVC T-fitting that accommodates the diameter of the stack as well as the 1 1/2-inch sink vent pipe.