AAV to Fix Siphon of Tub Trap?

[MechTech]

The vent for the full bathroom is downstream of both the toilet and tub. When the toilet flushes air is pulled in through the tub trap. I've tested using a manometer, and I'm sure it's due to vacuum in the line and not positive pressure. I'd like to install an AAV for the tub, downstream of the trap but before joining the 4" pipe from the toilet. My question is, can the AAV be installed 4" above that drain line, or does it need to be run up through the wall above the water line of the tub?

edit - I've already established that the vent downstream is not plugged/clogged

 

[Terry]

Instructions allow for 4" above the line. Like anyone else, higher is always better if possible.

 

[Sponsor]

 

[MechTech]

Thanks for the response Terry! The valve I have is an Oatey, but looking at the Studor installation instructions I found the attached picture which is pretty much exactly what I'm planning except the AAV will be beneath the floor (but still accessible for replacement).

 

[Reach4]

Looking at https://www.oatey.com/ASSETS/DOCUMENTS/ITEMS/EN/Submittal_DFU_Combined_R7.pdf it looks to me as if the 4 inches is from the bottom of the AAV. From the top of the AAV it looks like 6 inches above the top of the trap arm. I am not sure if this includes the space needed to change out the AAV, so would more space be needed to unscrew the failed AAV and screw in the new one?

 

[MechTech]

Reach4, a little space will still be needed above for replacement. The floor joists are old full dimension 2x8, and the drain lines are all below that, so I have about a 12" clearance above to work with if I hide it down there. I'm also considering running it up the wall behind the access panel for shower, but that's quite a bit of extra work.

 

[Reach4]

Reach4, a little space will still be needed above for replacement. The floor joists are old full dimension 2x8, and the drain lines are all below that, so I have about a 12" clearance above to work with if I hide it down there. I'm also considering running it up the wall behind the access panel for shower, but that's quite a bit of extra work.

I am not a plumber, and I have not worked with an AAV. I was just trying to follow the documents. Maybe you could set up your trap in a way that can be disassembled and let you get to the AAV for replacement.