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Old 08-17-2010, 11:10 PM   #16
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PEX vs copper pricing


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I have used it recently in renovationtions but wonder if there are not flow restrictions since the PEX fittings have a smaller inner diameter that copper fittings. I know that is is not recommended for a tub spout due to water diverting up into the shower head. I am close to turning on the new plumbing where I have replaced copper with PEX so I guess I will have my answer soon.
That's a good question, anyone want to weigh in on this?


Further, I've noticed a lot of PEX installations with right angle elbows installed instead of just using sweeps of PEX to make turns. Does this effect flow in any way?

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Old 08-17-2010, 11:19 PM   #17
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PEX vs copper pricing


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That's a good question, anyone want to weigh in on this?


Further, I've noticed a lot of PEX installations with right angle elbows installed instead of just using sweeps of PEX to make turns. Does this effect flow in any way?
I've always used bend supports because they're cheaper than 90s and take less time to install. But when a pipe comes up from the floor directly under a fixture, a 90 will make it come straight up and not at an angle. Also I don't know about a tub spout w/ pex... you can't screw a pex male adapter into a tub spout (it'll just spin) so i've always done it in copper. I suppose you could use one that slips on the outside of the pipe, but i've never tried it.
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Old 08-17-2010, 11:23 PM   #18
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PEX vs copper pricing


Yes it is correct that PEX of the same nominal diameter as copper type L has a smaller internal diameter. It is not correct to conclude that there are flow restrictions due to the smaller diameter. There are other factors that enter into the flow calculation, for example there are typically fewer fitting used in a PEX installation since PEX bends and hard copper does not, and PEX comes in long rolls whereas hard copper typically comes in ten foot lengths.

Since each fitting has an equivalent pipe length, and PEX has a lower roughness coefficient than copper, steel or galvanized, each installation must be analyzed fully before the actual flow rate can be determined. I did my house in PEX, easy installation, no leaks, few fittings, but in my house my relatively acidic water had eaten the copper up over a 40 year period (copper is not recommended with water that has a pH less than about 6.5), and PEX is effectively immune to acidic water, so PEX was a no brainer. I did use copper for the connection between my shower diverter and the showerhead, because the Kohler install sheet specifically stated that PEX was not acceptable in this case due to the smaller diameter, so I guess in 40 years the owner of the house will need to replace that piece of copper. Se la vie.
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Old 08-18-2010, 12:30 AM   #19
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PEX vs copper pricing


@ Daniel Holzman, Thanks for the explaination. I was trying figure out how to say that
The water system in a house is sized based on the proposed water fixture units per fixture as well as existing water pressure, length of run and elevation rise. Most plumbers use "a rule of thumb" to decide how many fixtures to put on a 1/2" branch line. IMO, they tend to over size. Better safe then sorry approach.
When I make up tub/shower valves I like to prefab the valve, shower arm, tub stub out and water drops using copper. It helps to make a more rigid assembly. Never stub a tub out in pex. Since the ID is smaller then copper's it offers more resistance to flow and the excess will go up the shower riser.

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