The 3/4 Rule (Hot and cold water)

[juenriq]

I am a junior plumbing designer in the Los Angeles area, can anyone explain the 3/4 rule meaning for example a sink is worth 2 fixture unites with the 3/4 rule it is 1.5 fixture units.

Thanks

 

[PEDARRIN2]

Never heard of a 3/4 rule.

In the IPC, a sink has 2 drainage fixture units. The factor might have something to do with low flow fixtures, but doesn't have anything to do with code.

 

[krafa]

A few things I can think of
1. So it runs cold, then hot, then cold and stays cold? I take it you have a re-circulating line? If so and the lines are close to each other and uninsulated it's entirely possible to have the hot line heat the cold while the water is sitting. Their isn't anything you can really do about it besides insulate the pipes, get them further away from each other, or remove the re-circulating loop.
2. Did you replace any plumbing? It's possible you crossed a hot and cold line somewhere.
3. For some reason prior to you owning the house the hot and cold lines may have been tied together with a ball valve, perhaps an attempt at a home made mixing valve of sorts. Stuffing insulation may have knocked the handle on the valve open. Plummer

 

[MechEngNCPE]

Krafa what are you talking about???

 

[IRstuff]

I think you are referring to cost estimating? That may be someone's "rule" but generally, that's not how the National Construction Estimator is organized.

yeah, I finally get to use that book... ;-)

TTFN
faq731-376

 

[MechEngNCPE]

I think he's talking about some kind of 75% diversity rule, I'm not sure what it is though. Just read the IPC section on fixture units. It has everything you need.

 

[juenriq]

Yes that is exactly what I am talking about the 75% diversity rule.