What is Plumbing Venting?

What is Plumbing Venting? Plumbing venting is the waste system is vented to allow free air circulation within the system to allow the pressure on the trap seals to reduce and to get rid of foul gas odors that are caused by sewage. The venting must be tied into the stack. The method that is used to vent the waste system will depend on where the fixture are located and how they are put together.

The venting system or the plumbing vents have pipes that lead from the fixtures to the outside usually from the roof. The vents give relief of sewer gases that come from the oxygen for aerobic sewage digestion and from the maintenance of the trap water seal that do prevent sewer gases from coming into the building.

Every fixture is required to have an internal or external trap, you can have one or the other but double tapping is against the Uniform Plumbers Code. Barring any exceptions, every plumbing fixture must have an attached vent. The tops of the stacks must be vented as well through stack vents.

Most residential buildings have drainage systems that are vented through the roof. The DWV pipe is either ABS or PVC rated plastic pipe that has a flasher to prevent water from getting into the building. Older homes may use copper, iron, lead or clay.

A blocked vent is a relatively common problem that is causes by anything from leaves to dead animals or even ice dams from cold weather. There may be signs of a blocked vent from bubbles in the toilet bowl after it is flushed, slow drainage or empty traps and sewage gases that are sensed in the building. There are different styles of vents here are a few.

Unit venting allows two of the same type of fixtures to use the same stack fittings. The waste drains of two fixtures must be at the same height from the floor. The wet venting lets the drain line of one fixture to act as a vent line for another fixture. The vent size will depend on the amount of space between the trap outlets.

Circuit venting is used with two or more fixtures, for example, bathrooms in stores or buildings when the fixtures are installed in a row. The circuit vent is connected to the waste drain line that is located between the last two fixtures in the row. The circuit vent is connected to the main vent.

A water seal will also stop the sewage from coming into the building. It is a column of water inside a fixture trap. The column is maintained by the atmospheric pressure coming from the venting which is 14.7 pounds per square inch at sea level. Water closets have built in traps that can provide visible water seals.

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