Does a Washing Machine Drain Stack Need to Be Vented?

Sewer-Gas Management

• The vent pipes in your house’s plumbing help with the management of sewer gases. Sewer gases build up in the drainpipes inside the house’s plumbing and must have somewhere to go. The curving trap pieces on the various plumbing fixtures’ drainpipes stay full of water, blocking the progression of sewer gases to the fixtures’ drain openings. The vent pipes run up through your house’s roof, allowing the sewer gases to flow outside of the house.

Air-Pressure Management

• The vent pipes in your house’s plumbing help manage the air pressure in the drainpipes. Whenever waste water flows down the drainpipes, it takes some air in the pipes with it. If the air that flows down the drainpipes with the waste water is not replaced, the washing machine and other plumbing fixtures’ drains may not operate correctly, acting as if they have clogs or draining the water out of the trap pieces. The vent pipes allow air to flow into the drainpipes to replace any air lost down the drainpipes.

Drain Overflow

• Not installing a vent pipe on the washing machines drain stack can lead to drains overflowing in the house. Every drainpipe in the house’s plumbing system connects to larger pipes, which all eventually connect to the sewer drain pipe, or the pipe that connects the house’s plumbing to the municipal sewer system. If the washing machine’s drain has a problem with venting, causing an air pressure imbalance or sewer gas problem, that can lead to the washing machine or other plumbing fixture’s drain to overflow.

Sewer-Gas Dangers

• Not venting a plumbing fixture’s drainpipes can allow sewer gases to enter your house. Sewer gases not only smell offensive, but they can put your health at risk. The various gases that may be present in sewer gases can cause you to feel nauseated, light-headed or to even faint or pass away from asphyxiation. Sewer gases can also contain methane and other flammable gases, meaning the sewer gases may cause a fire or explosion if they are exposed to an open flame or sparks in your house.