Plumbing vents are necessary to keep drains flowing, supply fresh air, and get stale gases out of the house. Plumbers use different vents depending on house configuration, fixture, and vent purpose. Below are different types of plumbing vents.
A true vent is the most common plumbing vent; it is what most people mean when discussing vents. A true vent is a vertical pipe that runs from the drain line to the house's roof. The vent allows drain gases to escape out of the house. The plumber will connect the true vent in such a way that it serves multiple fixtures within the house.
An auxiliary vent works like a true vent: it removes drain gases. However, unlike a true vent, an auxiliary vent serves one specific vent. The plumber connects one end of the auxiliary vent to the drain line near the fixture it serves and the other to the main vent. The vent channels the gases to the true vent, dispelling them outside the house.
Plumbers use a common vent when they install two fixtures back-to-back. Consider two sinks in different rooms installed back-to-back. You don't need separate venting for the sinks. Rather, the plumber can install a common vent and connect each sink to the vent.
A wet vent serves two purposes: a drainpipe and a vent. For example, you can use a wet vent to drain toilet waste and vent drain gases out of the house. For the wet vent to work effectively, it must be so big that the waste it drains can never fill it. Otherwise, the drain function might interfere with the vent function.
A loop vent runs under the floor and creates a loop inside the cabinet sink. The vent makes sense for a freestanding fixture, such as a sink on a kitchen island. Connecting a vertical vent to a freestanding fixture is impractical, so the loop vent provides a good alternative.
Air Admittance Valve
An air admittance valve (AAV) is ideal when you cannot connect a plumbing fixture to the main house vent. The AAV is a one-way valve that serves the specific fixture. As the name suggests, the vent supplies the fixture with air to prevent negative air pressure from interfering with plumbing operations, such as drain flow.
Note that your local building codes may determine which vent to use. Your plumber will advise you on which vents your local authority allows. For more information on plumbing installations, contact a professional near you.