How far should 3/4" copper be run?

[Gregavi]

Greetings,
I am a General Contractor and I have used many professional plumbers over the years. For a bathroom for instance, I have had some plumbers run 3/4" copper all the way to the the shower valve or faucet or tub valve and then adapt down to the necessary 1/2" for connection. I have had other plumbers adapt down to 1/2" right after the last "branch off" and run the 1/2" the rest of the way. In either case, they always tell me their way is best. Opinions??? What is the better way and why? Leave it 3/4" as long as possible or adapt down after the last "branch off"?

Thanks in advance.

 

[Terry]

For most tub/shower valves I would run 1/2" from the last branch.
There is an argument for running 3/4" if you have PEX, which is a smaller diameter.
HansGrohe has an i-Box that takes 3/4", but if you're only running it like a tub shower combination, I don't see how 3/4" would help.
The i-Box does allow for more coming off the valve though, and that may be why they have that.

Grohe has 3/4" Roman tub valves, though most like Moen and Delta are 1/2" valves.
To fill those large "planters" in the Masters, I kind of like the high volume valves.

 

[Sponsor]

 

[Jadnashua]

The area of the opening determines the maximum flow rate which has two issues: you can get more flow if needed going bigger (say filling a large tub or a multi-head shower and keep the flow and pressure up), but, it also means more cold water to flush out of the lines before you get that hot water where you want it (making the case for a hot water recycling system).

It's simple math, the area of the opening is R*R (* pi), and if you just use the radius of 1/2" and 3/4" pipe, the ratios stay the same: 0.25*0.25=0.0625 in relation to 0.140625, or a ratio of 1:2.25 - the 3/4" pipe can flow 2.25x more water. Now, you have to decide if you need that increased flow or not.

If you believe the copper tubing institute and keep the max flow rates of 5fps, that's not much in gpm on a hot water pipe in 1/2". Perfectly fine for a single and maybe two shower heads (depending on your cold water temperature), but it starts to get meager when you start adding them, or want to fill a big soaker tub in a timely fashion.

Like many things in life, there is no one answer that is correct all of the time. Since you do not know what may happen in a remodel down the road, 3/4" supply pipes leave lots of options open, but it does cost a bit more (not as much as tearing out and redoing, though).

 

[hj]

The critical measurement is the opening in the faucet and very, very few have an opening even close to a 1/2" pipe, so running 3/4 does not give any advantage.

 

[Gregavi]

Thanks to all.
HJ makes a great point.

Very informative. I do live in drought-ridden SoCal but we're going to run 3/4" all the way anyway and use a recirc pump to solve the water waste issue.