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Traps are installed at Plumbing fixtures to protect the premises and occupants from offensive and hazardous gasses. Vents are installed immediately adjacent to the traps to protect the trap from losing its water seal from the syphonic action caused by the draining water running through it. They are necessary for the plumbing system to work properly and safely. If you cannot carry the vent through the roof, some states and municipalities allow the use of an "air admittance valve", sometimes called a "johnny vent" in lieu of a vent-thru-roof. It is a small and inexpensive (plastic and rubber, under $10.) device consisting primarily of a spring loaded rubber disc which closes to pressure pushing out from within and opens to suction, which happens when the fixture is draining, or finishing the drain cycle. A trap seal loss can allow carcinogenic and flammable sewer fumes fumes to enter the home.

The use of AAV's sometimes called pro vents are illegal to use in the better plumbing codes as one would be kind of fool hardy to trut a spring and a piece of rubber to protect ones health.

Even the codes that do allow these garbage connectors do have certain requirements and restrictions.

A Vent through the roof is the best way to go and depending on weather conditions you may be required to use a 4" pipe to prevent hoarfrost

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โˆ™ 2007-11-15 00:41:22
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Q: What is a venting for on drains and what if you can't go up through the roof to vent the drains?
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