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Air Admittance Valve - waste stack replacement

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  • Air Admittance Valve - waste stack replacement

    Hi all. I am currently renovating and our toilet system is very old but functional.

    The only improvement I am doing is to replace the vent stack because the existing one is 100mm copper up and out from under the eaves.

    First thought was to replace with a compact and modern 40mm stack on the same route but the plumbing supplier convinced me to fit an AAV (Air admittance valve) instead which can terminate directly above the waste line.

    My question is: can an AAV be used in NZ for the only vent, or is it only for additional vents on the same line which already has a full height stack?

    My fear is that the AAV will allow flow by relieving negative pressure, but will not vent gas buildup?

    The total waste pipe is only 3m long into sewage.


  • #2
    this work should be done by a registered plumber

    what does he say?


    • #3
      I second JTB - a plumber would give a very quick answer.
      Unless a registered plumber comes on here with an answer anything written here is opinion.


      • #4
        Originally posted by John the builder View Post
        this work should be done by a registered plumber

        what does he say?
        Thanks JTB for your useful reply. I'm not changing the form or functionality of the waste system, just replacing a component which is damaged like for like.

        Much like I would doubt you would call a plumber to fix the s trap under your sink - and nor would a plumber be likely bothered to turn up for 5 minutes work.

        None the less, if an answer is not easily available I will ring around for plumbers who might be able to assist.


        • #5
          AAVs can only be used on branch drains connected to an open vented main drain. See NZBC G13/as1


          • #6
            Thanks geoffm. Found it!

            Stack vent: All stacks discharging to another stack or to a drain require an open vent, sized in accordance with
            Table 6. Venting with an air admittance valve is permitted only on second and subsequent stacks as at least one
            open vent (the stack vent, if acting as main drain vent) is required to ventilate the drain