Horizontal branch vent length

I have a long vent for a vanity, 30' where 23' is horizontal to a 2" vent stack.
UPC says 120' max and 1/3 of which (40') can be horizontal.
My question is: does this mean total horizontal vent length in the entire house
Or , is 40' allowed for the new branch vent with 3 dfu's ?

I can use 2" vent if that helps. Oh, the damn thing will have to bend a total of 270 degrees as well.

Thanks.

Are you saying the trap arm (horizontal pipe coming out of the P-trap) from the vanity is 23" until it reaches the vent?

A photo or diagram could help determine your situation.

Will have to learn to do the photo.
The vent will bend 90 degrees to vertical off of a 1 foot trap arm.
The vent will rise 6' , bend 90 degree to horizontal, run 2 feet, bend 90
degrees, run 8 feet, bend 90 degrees run 13 feet to the dry vent stack.
29 feet horizontal vent, bending 270 degrees . It will run in a 2 1/2 inch
raceway near top of wall , slope towards vanity and possibly be 1 pipe size larger than required 1.5" . The shower vent will also connect to this lomg horizontal vent 8 feet from the vent stack.
I have an 8" sheet metal duct in the ceiling blocking a more direct route. I have heard that in Ma. that Air Admit. Valve for vanity is a no.
Hope this explanation helps.
thanks.

I suppose i could let the plumber design and worry about this but,
Stubborn dog with bone here.

So, are you saying the trap arm will bend 90 degrees BEFORE reaching a vent? Or are you saying the trap arm will connect with a vent with a sanitary tee and then bend up with a 90 for 6' and then have more bends?

From what I understand, once the trap arm reaches the vent, the only limitation to the length of the branch vent is based on how much room you have for rise and run. It needs to rise at least 1/4" per ft for horizontal runs.

So, is this whole run from 6' up all horizontal and just bending to the side?

"Trap arm will connect with a vent withina foot with a sanitary tee and then bend up 90 for 6' to the top of the wall and Then run 23' , 270 degrees bend along 3 walls to reach the vent stack.
i have read UPC on the issue of horizontal vent and cant interpret it.
But the code says if you increase vent by 1 pipe size "the limit does not apply" and this just confuses more.
plumber is comimg in couple days. Hope this can be done.

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Jeez, after a couple weeksor so,i looked at this thread again and finally
"Got" it . The diagram is a solution. Thanks. Gawd am I thick.

as long as you maintain the same sq inchs. if you try and cheat, you will create a duct that whistles

Look in chapter 10 of the plumbing code. Also any horizontal venting must be sloped back to the fixture's trap. Air goes up, water goes back to the trap.
Proper venting is really important so make sure your sized correctly.