What types of fixtures are typically duel vented?

Dual venting is a plumbing practice used primarily to ensure proper air circulation and drainage for specific fixtures within a plumbing system. Fixtures that are typically dual vented include basins, sinks, laundry tubs, and wall-hung urinals.

The reason for this design is that these fixtures often experience varying drainage patterns and can benefit from having two venting paths to ensure that they operate efficiently without creating negative pressure. This helps prevent situations like siphoning, which can lead to sewage gases entering living spaces as well as ensuring quick and effective drainage.

In contrast, the other categories listed do not commonly require dual venting because they either operate with different plumbing requirements or do not face the same challenges that necessitate dual vents. For example, toilets, showers, and bathtubs usually rely on single-vent systems where effective drainage and trap protection can be maintained with sufficient venting through a single outlet. Similarly, appliances like dishwashers and water heaters often have dedicated venting strategies or do not directly connect to a venting system in the same way that sinks and urinals do.

Thus, basins, sinks, laundry tubs, and wall-hung urinals are the fixtures that typically require dual venting to maintain optimal function within the plumbing system.