What is a common vent?

What is a common vent?

• A. An individual vent that vents two traps or trapped fixtures as a common vent
• B. A vent that serves a single fixture only
• C. A vent installed inside the wall
• D. A vent that runs outside the building

Answer: (A)

A common vent is a single vent that serves two traps or trapped fixtures as a shared vent. This arrangement allows air to enter the drainage system for multiple fixtures, helping to prevent siphoning of the trap seals when water flows. It’s used when two fixtures are close enough to be vented by one vent, rather than each fixture needing its own individual vent. Think of it as a single vent line positioned to vent the traps of two fixtures, so both are protected from negative pressure during drainage. The other options describe characteristics like venting only one fixture, or just where the vent is located (inside a wall or outside the building), but they don’t define the concept of venting two fixtures with one shared vent.

A common vent is a single vent that serves two traps or trapped fixtures as a shared vent. This arrangement allows air to enter the drainage system for multiple fixtures, helping to prevent siphoning of the trap seals when water flows. It’s used when two fixtures are close enough to be vented by one vent, rather than each fixture needing its own individual vent.

Think of it as a single vent line positioned to vent the traps of two fixtures, so both are protected from negative pressure during drainage. The other options describe characteristics like venting only one fixture, or just where the vent is located (inside a wall or outside the building), but they don’t define the concept of venting two fixtures with one shared vent.