What Are the Effects of a Clogged Plumbing Vent?

A vent stack extends upward from the roof of every building that has waste plumbing. The function of this 2- or 3-inch pipe is to admit air into the drainage system, and when it gets blocked, the flow of water can slow and stop, and sewer gases can enter the house.

Negative Pressure

When the vents get blocked, the flow of water creates negative pressure in the drain pipes, and the resulting force of suction stops water from flowing and sucks air in through P-traps. As a result, you'll notice slow drainage and you may hear gurgling sounds coming from drain openings. If the condition persists, you'll start noticing more frequent blockages in the pipes because the slowly flowing water allows sediment to settle more easily. You likely have a vent problem when you can't clear a slowly flowing drain with a plunger, auger or drain cleaner.

Extreme Blockages

When the vents become totally blocked, which can happen when debris or even small animals fall into the vent pipe, the vacuum can become strong enough to suck water out of P-traps. When this happens, you won't hear gurgling anymore, but you'll be able to smell sewer gases in the rooms where the affected fixtures are located. This is a problem that needs immediate attention. Besides being odorous, empty P-traps are unhygienic and can cause disease for you and your family.

About the Author

Chris Deziel


Photo Credits

  • Brand X Pictures/Brand X Pictures/Getty Images
bibliography-icon icon for annotation tool Cite this Article