AAV-Are these Installations both done correctly?

[Daniel A]

Hi folks. I need to install an Air Admittance Valve for my kitchen sink. I have seen more than a few pictures of these installed under sinks (many of which look like they're done wrong.) My question specifically pertains to where the vent should go. In some pictures, I see the vent installed at the top of a drain that goes straight down, vertically into a wall or floor. In others, I see the vent installed with a sanitary tee on a horizontal pipe that then connects to a pipe that goes downward (see pictures.) Are both these methods acceptable? For some reason, I feel that a vent installed at the top of a downward vertical pipe is best.


AAV installed atop a horizontal pipe

AAV installed atop a vertical pipe

 

[Terry]

Yes. Same difference.
Both work.
The vertical uses the santee
The horizontal uses the combo or wye fitting.

 

[Sponsor]

 

[Daniel A]

Thanks Terry. A follow-up question: One of the above pictures shows the p-trap and subsequent piping, including up to the AAV stepped up to a 2" pipe while the other shows the whole thing as 1 1/2". Is one preferred over the other?

Thanks again.

 

[Terry]

Those are both 1-1/2"

Lavs can be 1.5" with 1.25" traps. I use a 1.5" and reduce out the top for the tail piece.

Kitchen sinks under UPC are 2" with 1.5" trap arms and traps.
IPC lets you use 1.5" I believe. Seems kinda small to me.