What Happens if Your Sink Does Not Have a Vent?

Importance

• Sink venting is all about air pressure, water and sanitation. The main house vents, or stacks, carry sewer gases out of the house. If sewer gases build up, they can cause illness and even death. The vents also balance air and water pressures when water or waste is expelled through a drain. If your sink does not have a vent, it may drain very slowly or not at all.

How They Work

• Vents work by introducing air to a closed loop system. This is simpler than it sounds. Think about a gas can that is used to fill lawn mowers. If you open just the nozzle end, the gas comes out very slowly -- and sloppily. However, if you pop open the air vent at the rear of the can, the gas flows faster and more smoothly. Sinks work in much the same way. When water runs into the sink, it displaces the air that is in the pipes. If the sink is vented, the air has a place to go. If it is not, the sink may not drain well.

History

• Before 1875, buildings with indoor plumbing had odor problems. Part of this was due to lack of venting, while another issue was the lack of plumbing traps. At a Master Plumbers Conference in 1874, the problem of odor and trap seals disappearing due to back pressure was addressed. At the conference, plumbers discovered that if a vent pipe was connected to a drain at the tap outlet, the problem was solved.

Adding a Vent

• If you have a sink that drains slowly and you have eliminated other possible causes of the slow draining, look for the vent that should be near the trap on the sink. Sometimes sinks have been installed without the installer knowing about plumbing and venting. Or perhaps the installer believed the sink was close enough to the main stack and did not need more venting. Whatever the reason for the lack of venting, you can resolve the issue. You can either tie into the main stack vent for that area of the house, or you can add an air admittance valve.