Plumbing codes -- PVC drain line size

Probably not. You'd have to do a study of fixture units but fixtures for 3 units probably exceeds the capacity of 3" stack. (The rated capacity of 4" pipe is roughly 10X that of 3")

Further, the use of PVC may be restricted by local ordinance.

Your call whether you ask the local authorities, who can give you the true answer...

Jim

go with 4.

and be aware if you convert to PVC you will get NOISE COMPLAINTS.

every time anyone uses water everyone will hear the noise

??

Plumbers use funny math ? I assume he is talking about the number of fixtures it will serve. Like the electrical code, they assume diversity, all the toilets won't be flushed at the same time ... unless it is half time at the super bowl

Well, sure, but the same considerations apply to 3" pipe as well as 4". I think your first answer is the right one. :-)

I am not sure where the "10x" comes from but there are 2 tables in the Fla plumbing code (based on the ICC codes) that talk about fixture units and the number of units for a given pipe size at a given slope (about 1/2 way down)

Thanks. I tried the link but it requires a login ID and password to access the site.

I guess they don't want people doing direct citations without joining the club You can navigate from here, look at the top hit, 2007 code

Sorry, I can't figure out what you mean by "look at the top hit". The link you provided takes me to:

Try this

Thanks. That worked. (I tried posting this on 3/1/2009 but I didn't see it here today so I'm posting it again).

A bit of an exaggeration perhaps, but not a huge one. Depending on the branch intervals the difference in capacity between 3" and 4" based on fixture units is around 5-8:1

To the OP: you can use 3" for a toilet if the pipe can handle the required fixture units on that branch and any connecting branches. If there's a lot draining into that line, or, more importantly, if your local code and building official deem it necessary, you will have to keep with the 4".

As an aside, you might consider using ABS drain pipe instead of PVC. ABS will take abuse and hard knocks a lot better than PVC.

Put on some goggles and go after small sections of each with a hammer and you'll see what I mean.

Do you often have people hitting your plumbing with hammers...? ;) Schedule 40 PVC is plenty tough enough for any residential situation.

Only if they're renters or those darned do-it-yourself home repair types. :))