Vent for toilet

[PrecisionPlum]

Why is a 2" line needed for a WC vent? I thought it could be 1/2 of the dia. of the drain line being vented.
So if a WC is on a 3" line, wouldn't the vent only be 1-1/2"?

Note: IPC code in my area.

 

[Pat the Plumber CIL]

Only allowed to drop 1 pipe size from the drain the vent serves

 

[breplum]

The code also evolved to be trouble free and smaller pipes would only invite trouble as far as back-ups clogging more readily in a vent pipe.
I had seen a plumbing engineer run the calcs in a plumbing trade magazine (Julius Ballanco was the engineer) years ago, and for sure, it calc'd out that you could prevent venting issues with a smaller vent in many pipe sizes.
But that is theoretical and not practical.

 

[Jeff Handy]

Plenty of birds, squirrels, rats, etc would neatly plug up a 1 1/2 inch vent if they went into it.

More chance of them decomposing and eventually self-clearing in a bigger vent, I would think.

Just my own goofy opinion.

 

[breplum]

Plenty of birds, squirrels, rats, etc would neatly plug up a 1 1/2 inch vent if they went into it.

More chance of them decomposing and eventually self-clearing in a bigger vent, I would think.

Just my own goofy opinion.

Jeff, I have a story: I had a Navien tankless trouble call. Located in an outdoor utility shed wherein after assesing the situation, diagnosing the issue and scratching my head, I disconnected the 2" PVC vent at the top of the unit and unearthed a dead rat.
The original installers did not fully extend through the roof, but pushed the pipe up into an existing and loose fitting and dangerous 5" "B" two piece roof jack and the critter climbed up and into that tight pipe.

 

[Jeff Handy]

Hah, the installers did not want to “vent”ure up onto the roof.
What a strange turn of e”vents”.
Maybe that ad”vent”urous rat was beguiled by that vexing “vent”uri they had created?
So glad that you did not “vent” your wrath on the hapless homeowner, and you discovered the installers’ crude in”vent”ion.
E”vent”ually!
This is a good story to tell at your next plumbing con”vent”ion.