air admittance valves

I want to cap my waste stack with an air admittance valve, so I can run my bathroom flue through the old pipe out through the roof.
I'm not clear what height I can cap it at though. It runs though a utility room containing the boiler, and the stack is joined by a toilet waste and a sink waste, close to the ground. Can I cap it
a) Whereever I like (preferably about as low as p b) Above the drain outlet of the boiler c) Somewhere else
I gather it's supposed to be above the "flood level" of the room, but I'm not clear what that is, particularly given that this is a first floor flat...
Ben
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Above the highest drain point. Try using HeopVo traps on the sink, basin and bath. http://www.hepworthplumbing.co.uk . Go to HepVo. Using these an air admittance valve is then not required.
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wrote:

There are only two types of AAV. Ones that are stuck open and stinking the place out, or those that are stuck closed leading to Jobbies Not Going Away. If you haven't got one of these infernal devices, on no account fit one. Mind you they do give me the chance to say "It's yer Durgo, missus."
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It's the flood level of the appliances, not the room IIRC. As far as I can tell, the idea is that if you filled all the drains up completely with water, it should pour out of somewhere below the AAV.
It's not to do with flooding in the 'Environment Agency' sense.
Will
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If you fit HepVo wastes to the sink you can cap it without using an AAV.

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On Thu, 18 Dec 2003 19:34:04 +0000 (UTC), "Rick Hughes"

Are they the ones with the integral AAV? If so the same disadvantages apply. If they are just antisyphon, then assuming the stack serves a WC, it probably won't flush properly with the stack capped.
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wrote:

HepVO traps are not so much fitted with integral AAVs, more they actually are AAVs themselves. I have cut our stack pipe down and have bath, basin and WC in first floor bathroom working perfectly well. And another WC and basin in the downstairs cloakroom also on the same stack. (Indeed, the bath empties at an almost frightening speed now.)
Brilliant devices. Hepworths were also very helpful with advice when I rang them before deciding on this route.
Rod
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wrote:

HepVo traps are not like normal wastes they do not use water as a seal ... and the design allows easy air ingress which is what you want to vent SV stacks ... it is not a question of allowing air to escape - the opposite, you want air to get in when a WC is flushed to avoid negative pressure.
It's this negative pressure that causes the problem ... it sucks water out of traps.
Rick
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On Sat, 20 Dec 2003 20:17:02 +0000 (UTC), "Rick Hughes"

I never suggested it was about allowing air to escape.

Indeed. If there are no traps to suck, the bog doesn't flush properly.
If the HepVo doesn't use a water seal, what does it use, some mechanical device? Hopefully more reliable than an AAV.
Actually there is another issue related to a stackless system. The stack may be used to vent the drainage system or septic tank where used, doing away with the stack can lead to smell problems.
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wrote:

AAV.
...
out
A membrane.

Usually every 4th or 5th house, or the end of a run, such as cul-de-sacs, requires the stack intact with no AAV or HepVo. See local water authority for details.
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