The main problem with using an Air Admittance Valve instead of a Soil Vent Pipe, as discussed earlier, is that by preventing the gases from escaping through the top of the soil stack you are causing them to be forced down into the main drains and sewer system instead.
AAV location
An AAV should be located within the maximum developed length permitted for the vent. It must be located a minimum of 4” above the horizontal branch drain, 6” above any insulation material and within 15 degrees of vertical.
AAVs, have NOTHING to do with how fast the tub drains, unless you already have another problem with the drain system. If anything, they will keep it from draining TOO quickly and creating siphonage. WHERE you need vents, or AAVs, has as much to do with what is flowing past the connection as it does distance.
The AAV should be located: Within the maximum developed length permitted for the vent. A minimum of 4 inches above the horizontal branch drain.
Air admittance valves are not permitted in spaces where pressure conditions adversely affect the valve's operation. They are also not allowed in concealed wall and ceiling spaces used as plenums as part of an air distribution system that is under negative or positive pressure.
Air admittance valves are typically placed between the P-trap of a fixture and the drain line. They're usually mounted on one leg of a sanitary tee, with the other leg going to the drain. The unit must be placed per local codes and the manufacturer's instructions.
Air admittance valves have a typical life expectancy of 20-30 years, so if you start to have issues with sewer gases or smells being released around your sink or in the attic-wherever installed- the air admittance valve could be faulty or failed and should be replaced as soon as possible.
The short answer is a minimum of 200mm above any water entry point. So if you imagine your soil pipe run, then durgo valve / AAV must be fitted above the highest connection to the soil pipe from any sink, bath or toilet that is connected to it.
If a sink drain is not properly vented, it can cause a variety of problems, including slow drainage, gurgling sounds, and foul odors.
In order for a liquid to come out, air must come in. All DWV plumbing systems require at least one vent penetration through the roof line, which allows air to enter the system, while also permitting sewer gas to escape.
Air Ducts Near the Ceiling Are Most Effective
Many people don't realize this because it is common to see air vents located near the floor in older homes. With vents near the floor, however, furniture often ends up blocking vents and causing the air to get trapped.
Automatic air vents are spring type devices often referred to as in-line or cheater vents, while air admittance valves have no spring. Air admittance valves are more expensive and are approved in many jurisdictions where in-line and cheater vents are not because of their moving parts (springs).
The Studor vent lets that air to be sucked in the pipe during water flow but doesn't let sewer gas escape out. Code is the thing that determines pipe size and also water flow. Hence no studor vents are permitted to toilets because more air is required to keep water flow going with more waste added to the toilet.
Individual and branch-type AAVs shall not be located not less than 4 inches (102 mm) above the horizontal branch drain or fixture drain being vented. See Figure 4, Examples 1, 2 and 3. AAVs shall be accessible, should replacement be required.
Air admittance valves often feature rubber seals, to help create a complete seal, increasing the effectiveness of the valve and preventing any odours from escaping through small gaps.
STUDOR AAVs' location must allow for adequate air to enter the valve. An opening shall be provided in a wall or attic space lacking ventilation. Locating the valve in a sink or vanity cabinet is acceptable.
The valve should be placed on a soil pipe that is at least 200mm above any water entry pipe or the highest point that wastewater will normally reach in the soil pipe. This is generally at the end of a soil pipe, but can also be added inline, using a soil pipe junction.
They are not illegal in California as a state because California Plumbing Code allows "Engineered Vent Systems" see Section 911.0.
The external soil stack may be terminated below the roofline which reduces the amount of soil pipe and fittings required. The AAV may be installed at a minimum height of 200mm above the highest wet branch connection.
Sometimes called "cheaters," these tubular, spring-loaded $5 vents are rated for only 1/2 DFU (drainage fixture unit), and are not allowed under most building codes.
A plumbing vent does not necessarily have to go straight up. While it is common for vents to run vertically and extend through the roof, there are alternative venting methods available, including: Horizontal vents: These vents run parallel to the building's floor and connect to a vertical vent or vent stack.