# Why not 3/8 PEX for all the domestic HW and CW?



## UpNorth (May 17, 2007)

Home runs to all fixtures, from the manifold. Max length 25 feet.


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## Tinstaafl (Jan 6, 2008)

Your house? Heck, use 1/4" if you feel like it.


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## TimelessQuality (Sep 23, 2007)

Sounds Great!:thumbsup: 

Prolly go with sharkbites too:thumbup:


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## KillerToiletSpider (May 27, 2007)

You can't use PEX here.


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## [email protected] (Jan 10, 2010)

DIY alert. :laughing: Use 1 1/4" . Or hire a plumber.:thumbsup:


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## Leo G (May 12, 2005)

1.25/gpm flow rate


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## Inner10 (Mar 12, 2009)

Cuts the water bill down, just takes a while to fill the tub. :laughing:


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## Mike's Plumbing (Jul 19, 2010)

......and how much would you be saving by being "different"? What would be the point? 1/2" pex is cheap and so is cpvc. Just do it normal and spend the extra $20.:laughing:

As long as your being different why not run your whole house with braided fixture supplies, just buy a bunch of couplings and order a skid of braided supplies. 

Mike


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## Smatt (Feb 22, 2011)

UpNorth said:


> Home runs to all fixtures, from the manifold. Max length 25 feet.


That's great if you want to isolate each fixture. Not only is that expensive you need a basement. Also most cases you will be grossly undersized.

An alternative method would be to run a home run to each bathroom group and branch from there. This is also costly, and from there you can isolate each bathroom and fixture if you have room/access to put a valve bank behind the tub/shower.
Length times distance you would seriously reduce your sustained pressure and it would not be prudent or cost effective!
Hopefully this is just a question.


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## cleveman (Dec 28, 2007)

It's a great idea. Why run 1/2" to a low-flow fixture which has 1/4" inside it?

The only problem is the plumbing code.

Also, the hot water will get to your fixture much quicker.

I ran 3/4" to a kitchen once, with pressure and flow in mind. Never again. You could turn it on and go use the bathroom and come back and wait a bit more for the hot water to get there. Of course the flow and pressure didn't matter because of the low flow fixture.

I've been filling up a 2 1/2 gallon oblong bucket in my kitchen sink lately to take with me to wipe down glue and stuff with. I'll have to time it sometime. It takes forever to fill up that bucket. That fixture is plumbed with the standard 1/2" pipe.


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## mrd999 (Mar 11, 2011)

IPC allows it with a homerun system up to 60ft for pretty much any common fixture except sillcocks. See Table 604.5. Don't think you'd want the tub that small unless maybe it was a real short line.


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## plumber4200 (Feb 25, 2011)

Up North, 
I am not going to get all snotty with you like some, but I believe it will cost you more in the long run and may not benefit you at all. In theory i like the manabloc and idea of 3/8" lines but I never wanted to buy extra crimpers, and fittings and pipe that I may never use again. Also, around here they only sell it at Lowes, no pro plumbing supply stores sell it and if you are worried about wasting water just add a 1/2" return line and the smallest grundfos pump and insulate your lines and you wont waste much water and the electricity bills will not kill you either. Hope this helps. Never any harm in thinking outside the box.

Pat


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## Smatt (Feb 22, 2011)

cleveman said:


> It's a great idea. Why run 1/2" to a low-flow fixture which has 1/4" inside it?
> 
> The only problem is the plumbing code.
> 
> ...


Try cleaning your aerator


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## protechplumbing (Oct 10, 2008)

That would put your velocity beyond what the material manufacturer allows in their design specifications for many of your fixtures. This would make it illegal in just about every one of the country's codes.

Also, you would void your warranty and most likely flood your home 15-20 years down the line from the subsequent cavitation damage to the fittings.

Call a licensed plumber before you get into anymore trouble.


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## mrd999 (Mar 11, 2011)

protechplumbing said:


> That would put your velocity beyond what the material manufacturer allows in their design specifications for many of your fixtures. This would make it illegal in just about every one of the country's codes.


So if a fixture is designed to connect to a 3/8 flexible line, but its published design specifications list the velocity of water traveling through that 3/8 line as too high, then how are you supposed to connect the fixture? Or are you excluding all the sinks & toilets with 3/8 connections?


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## protechplumbing (Oct 10, 2008)

A fixture supply tube is a replaceable item outside the wall and is not classified the same as distribution piping in the codes.

Also, the fixtures I was referring to do not utilize a supply tube so your point is moot.

I repeat: Call a licensed plumber before you get into anymore trouble. 



mrd999 said:


> So if a fixture is designed to connect to a 3/8 flexible line, but its published design specifications list the velocity of water traveling through that 3/8 line as too high, then how are you supposed to connect the fixture? Or are you excluding all the sinks & toilets with 3/8 connections?


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## mrd999 (Mar 11, 2011)

protechplumbing said:


> A fixture supply tube is a replaceable item outside the wall and is not classified the same as distribution piping in the codes.


Ah.. so? The velocity of the water reaching the fixture doesn't care if it's in a fixture supply or distribution piping, only the size matters.



protechplumbing said:


> Also, the fixtures I was referring to do not utilize a supply tube so your point is moot.


OK, so why not just specify what fixtures you are referring to? Why are you being vague?



protechplumbing said:


> I repeat: Call a licensed plumber before you get into anymore trouble.


Who are you talking to? What trouble? The OP asked a legitimate question.


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## protechplumbing (Oct 10, 2008)

You may want to learn about fluid mechanics. Friction losses depend on viscosity, distance, hydraulic diameter and pipe wall roughness.



mrd999 said:


> Ah.. so? The velocity of the water reaching the fixture doesn't care if it's in a *fixture supply or distribution piping, only the size matters.*
> 
> OK, so why not just specify what fixtures you are referring to? Why are you being vague?
> 
> Who are you talking to? What trouble? The OP asked a legitimate question.


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## mrd999 (Mar 11, 2011)

protechplumbing said:


> You may want to learn about fluid mechanics. Friction losses depend on viscosity, distance, hydraulic diameter and pipe wall roughness.


I agree, fluid mechanics is an interesting field of study. However, I spoke not of friction losses, but of fluid velocity. This was in reference to your prior assertion:


protechplumbing said:


> That would put your velocity beyond what the material manufacturer allows ... and most likely flood your home 15-20 years down the line from the subsequent cavitation damage to the fittings.


Cavitation is a concern with high velocities, and my point was a 3/8 distribution line will provide equivalent expected velocities as a 3/8 supply line will, because they share the same hydraulic diameter.

In reference to frictional pressure losses, the IPC regulation I referred to earlier gives a 3/8 minimum distribution line for certain fixtures with known maximum flow rates and a limited developed length of 60ft. This prescriptive measure allows your 'average Joe' plumber to utilize an efficient design without being intimately familiar with fluid mechanics.


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## mrd999 (Mar 11, 2011)

Now that I think about it, however, my familiarity with the mechanics gives me the confidence to cite that IPC table. The reality is more complex than I am making it sound. The IPC specifies maximum velocities for flow through various materials, and those limits should be followed. It's easy to exceed those limits with 3/8 lines. 

However, if you have a straight run with no fittings from the manifold to the fixture, then the reality is your velocities are still safe. Cavitation worries come into play with susceptible materials and hard turns, for instance copper 90s. A 90-bend in continuous pex is tremendously more dependable, as both the material is more resilient and the radius of the bend is much, much greater.

But you are right, landing an unbroken 3/8 pex from the manifold to a fixture with 1/2in connections, and possibly sharp interior angles, such as a valve body, can exceed the engineered limits of the fixture.

So using 3/8" pex can be done, and within limits of code, but you must do so with care.


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