Bathroom Sink Venting Requirements
Many plumbers feel small 1.5 and 2-inch vent pipes will be enough to vent an entire home. Small vent pipes can choke off on the inside with ice in bitterly cold climates.
The switch must be located near the entrance to the bathroom. Ventilation. Remarkably enough, code does not require a ventilation fan. At a minimum, a window of at least 3 square feet should be provided. This window should be able to open at least halfway.
A sink needs a vent because the pressure put on the drain pipe when water flows down the drain pipe needs to equalize. The air needs to escape the drain pipe in order for the sink to vent. The best way to think about a sink vent is if you were to hold a pop bottle upside down and dump it out, it glugs out.
Vents exist primarily to allow air exchange in the pipes while water is flowing. Without them, the rushing water creates a vacuum that can slow the water or even stop it and can exert enough internal pressure on the pipes to crack joints. The plumbing code has specific requirements regarding pipe size and placement of sink vents.
The general rule is that smaller drainpipes—1-1/4 inches for bathroom sinks and 1-1/2 inches for kitchen sinks, for instance—lead to larger branch drains. These in turn lead to the main stack, which is the largest pipe of all—typically 4 inches. Because the main stack is also vertical, it will rarely clog.
Installing an AAV to vent a sink is fairly easy, whether you are replacing an old existing vent or putting one in for the first time. It basically involves tapping into the existing drain trap configuration to install an AAV via a new sanitary tee fitting and a short upward extension pipe.