System Description

To flow freely, drain pipes need air. Without air, water will glug down a drain like soda pop from a bottle. A plumbing vent plays the same role as that little second opening in a gasoline can. With the stopper closed, gas pours out slowly. But once the stopper is opened, the air entering the can allows the liquid to flow freely.

Also, the air supplied by a vent prevents siphoning action, which might otherwise pull water up out of traps and toilets and allow sewage gases to escape into the house. Instead, vents carry the gases through your roof. Sewer gas, composed largely of methane, is not only smelly, it is harmful and dangerous. Don't be tempted to install a substandard venting system, even if it means avoiding a lot of work.

A main vent is an extension of the waste stack and reaches upward through the roof. Branch vents tie into the main vent. Each and every plumbing fixture and appliance must be vented properly, either by tying into a main vent or by having a vent of its own that extends through the roof.

When installing a new fixture in a new location (not just replacing an existing fixture), venting is often the most difficult problem to overcome. Local codes require that venting adhere to specific dimension requirements. Research these requirements before you begin planning. Vent pipes are made of the same materials as drain pipes, although sometimes they are of smaller dimensions.