Frequently Asked Questions
Q. "I see that all of your AAV's (auto-vents or air admittance valves) shown on this page are mounted from the top going down (vertically mounted). Can I install any of these AAV's horizontally instead?"
A. To our knowledge, all of the auto-vents (AAV's) that we offer need to be installed vertically to operate correctly and safely.
Q. "What does DFU stand for?"
A. DFU stands for Drainage Fixture Unit. Each plumbing fixture or appliance is assigned a particular drainage fixture unit value as determined by the International Association of Plumbing and Mechanical Officials
(IAPMO). For example a kitchen sink is assigned 2 fixture units, but a bathroom sink is assigned 1 fixture unit. Drainage fixture units are used by plumbers and engineers to determine the size of piping needed for proper drainage and vent
systems. A listing of plumbing fixtures and appliances and their fixture unit values can be found in Chapter 7 of the Uniform Plumbing Code (UPC) book.
Q. "Can I use Air Admittance Valves (AAVs) only for my whole house?"
A. No, a minimum of one vent must be open to the atmosphere (outside the dwelling) to allow the release of positive pressure in the drain system to prevent possible trap blowout allowing sewer gas into the home/building.
A wet vent may also be an option; however, as always, check with your local code enforcement agency to ensure that your project will comply with code in your area.
Q. "How does an Air Admittance Valve work?"
A. An Air Admittance valve is a one-way valve designed to allow air to enter the drainage system when the pressure in the plumbing system is less than the atmospheric pressure. They are designed to close when
there is internal drain pressure to prevent any foul odor or gas from releasing out through the air admittance valve and entering your building.
When a plumbing fixture is operated and water drains out of the system, negative pressure causes the valve to open, allowing air to enter as needed to equalize the pressure and protect trap seals from siphoning. When the flow stops, gravity
closes the valve, preventing the escape of sewer gases through the valve.
The Air Admittance Valve must be installed a minimum of 4" higher than the trap as required by code. Installing the air admittance valve lower than 4" above the trap can cause drain waste to come in contact with the internal diaphragm.
Drain waste contact with the diaphragm can cause debris to become lodged in the diaphragm preventing it from sealing properly and allowing sewer gas and foul odor into the building.
As water flow subsides in the drain the air entering the drain from the Air Admittance valve flows above the water towards the trap weir effectively stopping the water flow. This keeps the trap from being siphoned dry which would
allow sewer gas and smell from entering the building. If the Air Admittance valve is installed below the trap, air would not be able to stop the siphoning action of the natural water flow and the trap would be siphoned dry.
See image below for sample diagram:
Q. "What does intumescent mean?"
A. Intumescent is a swelling process. The pad on the back of the fire rated box is made of a material that will swell up when heated helping to protect the box, and hopefully prevent a fire penetrating through
the box into the other side of the wall during a fire.
