I have attached a quick sketch of what I am looking to do. I am removing the wall that the 3" stack is in, and I was hoping that I could eliminate it as per the attached drawing. I am considering that the surface area of 1 1/2" pipe is 1.8 - so 4 of them would equal 7.2 square inches, and the 3" stack is 7.1 square inches, so I figure as long as I tie each 1 1/2" vent back into the 3" individually It should work; For some reason I am second guessing myself.

Anyone have any thoughts for me.

Thank you all in advance for reading/responding to my post.

Michael

Local code here requires that a minimum of a full sized 3" vent run all the way to the roof.

That is NOT a "universal" requirement. Many, if not most these days, just require and aggregate total AREA equal to the incoming pipe size, and often a 2" minimum for the toilet.

mass code requires one full size vent stack thru the roof, no matter if there are 101 smaller vents...

You need to check with the local code office, they can tell you specifically what the minimum requirements are in your area. The local jurisdiction has the final say.

the REASON for a full size vent thru roof:

FROST / SNOW will/may block a smaller vent (frost may form from the vent's condensation)

best practice (regardless of lesser code reqs); 4" thru the roof ending min 24" above

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

As I said it is a "local issue" and what applies to MA, may not be relevant to this person's area. And, if it is an IPC code area it may not even need a 2" vent for the toilet.

San Francisco requires a full size vent(equal to building drain) and there's not much snow/frost there.