Does PEX pipe reduces water flow


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Old 02-24-15, 04:26 PM
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Does PEX pipe reduces water flow

I bought Kohler facuet and transfer valve and I used PEX pipe fittings with SS Clamps. Transfer Valve was not working properly as water flow was not enough. So I called kohler and they suggested to change the PEX to copper as PEX tend to reduce the water flow and according to the installation guide they only support Copper pipe fittings.
My question is does it matter if I use PEX or Copper and does that effect the water flow?
PS. I have two bathrooms with same exact model and one works great with same PEX Pipe fittings and other is having issue.
Please let me know your suggestions.
 
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Old 02-24-15, 04:41 PM
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One of the plumbing gurus should be along with a pro answer, but I was reading an article the other day that mentioned that if you currently have 1/2" pipe and are switching to PEX you should go 3/4" because there is a difference in internal diameter than restricts the flow somewhat.
 
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Old 02-24-15, 04:46 PM
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That's a new one to me. Virtually all new homes are plumbed use PEX, so i cant imagine that being the issue.

If you account for all the elbows in copper, PEX should have less restrictions, even with the smaller flow through connections.

Remember, your supply lines are smaller than the fittings on PEX pipe.

It is possible you have a blockage somewhere on the lines under the sink or the faucet itself.
 
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Old 02-24-15, 05:00 PM
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Thats what kohler told me first that you might have some obstruction in the pipes or elbow so I changed them all including opened the transfer valve and cleaned it (Although I could not find anything) and then they told me that you should switch to copper.
I do have 1/2 inch PEX so I might try to expand it to 3/4 inch PEX and see if it makes any difference.
 
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Old 02-24-15, 05:15 PM
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The fact that you have an identical one that works fine with the same setup is a strong indication there is nothing wrong with using PEX.
 
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Old 02-24-15, 05:22 PM
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The pex should be fine.. IMO it would seem you have another issue..

Well? City water?
How long is the run?
What do these lines branch off from?
Did the plumber remove the cartridges of the divertors when soldering the adapters on??
Have you cleaned the shower head/body spray screens out?
Did someone remove the flow restrictors? ( This actually causes less pressure if you remove them)

Lots of varables,
 
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Old 02-24-15, 06:51 PM
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Here's an amateurs take on the diameter issue. I'm using 1/2" cinch clamps and fittings and I believe they have the same inside diameter as the crimp connectors. 1/2" pex has a slightly thicker wall than copper so the ID is slightly less than copper while the OD matches. But the cinch fittings have only a 3/8" ID so yes, if using cinch or (I believe) crimp on fittings you do encounter more resistance than with just copper. Corrections welcome and I'm just guessing on the crimp fittings, but it should be easy to measure.

Bud
 
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Old 02-24-15, 07:21 PM
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Though the ID of PEX is technically smaller than copper, I can't imagine the difference making any noticeable difference, especially only with one fixture. I'd have to believe your issue is somewhere else.

Most fixtures are flow-limited for energy efficiency and water savings and wouldn't use all the volume available on a 1/2" PEX or copper line. I believe 1/2" pipe is rated for about 10gpm at 60psi. Most fixtures are limited to 2.5gpm.
 
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Old 02-24-15, 08:47 PM
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Transfer Valve was not working properly as water flow was not enough.
Also transfer valve for what? Body sprays? Rain shower heads?
What was there befor?

These sprays and such can be 5gpm or more. x2 and a shower head you may be looking at 15gpm???

I belive 1/2 pipe can support 14gpm..

Maybe thats your issues...

But who knows.... too many variables and we do not have enough info....
 
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Old 02-25-15, 04:02 AM
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I agree with Mike. I installed a shower system for a client once and Delta specifically stater copper ONLY to the rain head. PEX or CPVC was fine for supply, but had too much friction/restriction to handle the GPM needed for that rise and run.
 
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Old 02-25-15, 05:04 AM
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Fittings and Pipe Sizes

Remember, your supply lines are smaller than the fittings on PEX pipe.
How can this be since the fitting goes inside the pipe?
 
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Old 02-25-15, 05:41 AM
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Supply lines are 3/8" ID. Such as to sinks and toilets from the stop valves. Pex fittings do restrict somewhat, however.
 
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Old 02-25-15, 06:33 AM
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Would 1/2" pex home-run be adequate for a tub fill--or is that one place you would recommend upping to 3/4"?
 
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Old 02-25-15, 07:23 AM
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Just like air ducts, every elbow in a copper supply line will reduce flow rate. With PEX pipe, virtually all runs are stright, with no fittings, thus allowing less restrictions. Also remember the shut off valves in a copper pipe system restrict flow the same as in a PEX system. At the end of the day, both systems will supply more than enough water to modern fixtures.

Fixture Flow Rate Comparison - Cross-Linked Polyethylene (PEX) Piping and Copper Tubing
 
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Old 02-25-15, 10:15 AM
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So Here is the info.
1. It is a city water and the main line to my 1st floor is copper . I remodeled both the bathrooms and had exact same system. Kohler R99903 for faucet and K728 for transfer valve to 2 accessories. One wall shower and second rain shower having both capacity of 2.2 GPM.
2. I did direct connection from faucet to both the shower head (wall shower head and rain shower) and the flow is enough to take shower.
3. There is no flow restrictors and also removed cartridge before soldering R99903 (which is my temperature control valve). From R99903 to Transfer valve K728 is all pex.

There are definately elbows from Transfer 2 elbows from transfer valve to the shower heads but its exact same on my other bathroom.
 
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Old 02-25-15, 10:23 AM
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Is this new setup on the same floor as the other bathroom?

When you say there is not enough flow, do you mean it is slow/low pressure, or not even enough flow for the water to come out of the head?
 
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Old 02-26-15, 09:07 AM
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In case anyone is interested here is some info:

1/2 inch PEX -------------> [O.D.=0.625], [I.D.= 0.475]

1/2 inch Type L Copper-->[O.D.=0.625], [I.D.= 0.545]
 
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Old 02-26-15, 09:48 AM
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Fixture Flow Rate Comparison - Cross-Linked Polyethylene (PEX) Piping and Copper Tubing
Keith - great link. Though it doesn't help the OP, I really enjoyed a scientific viewpoint on PEX vs. Copper flow.
 
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Old 02-26-15, 12:03 PM
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Thanks Zorfdt. No it doesn't solve the OP's problem, but it does show that PEX is not the cause of it as the manufacturer has told him.
 
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Old 02-26-15, 05:31 PM
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hi folks -

These are excerpts from the referenced study (post #14)

The tub/shower valves were changed using the same brand/model, but only with different respective piping connections.

Results and Discussion

Due to the minor differences in the tub/shower valves, the flow rate at the Test Fixture (TF) was slightly different between the PEX and copper systems. The PEX TF hot flow rate was measured at 1.7 gpm, while the copper TF hot flow rate was 1.5 gpm. On the cold side of the valve, the flow rates were 0.2 gpm and 0.5 gpm for the PEX and copper systems, respectively. All results are reported, including these small differences
Well I guess I can use my age as an excuse, lol (70+) but this eludes me. If the test fixture shower valves are the same except for connections (as they state above) in the Copper test and the PEX test, then why a ratio of 3:1 hot/cold for the copper vs. (approx.) 9:1 hot/cold for the PEX?

If the shower valve models are indeed the same except one has PEX connections and the other copper connections Ė isnít there indeed some kind of PEX vs. Copper lesson here? Maybe not - but it seems that way to me.
 
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Old 02-26-15, 05:45 PM
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I found it odd to that the flow rates were so low on the cold side, but I guess that is how these pressure balancing values must be designed to work. Even with the different hot and cold flow rates, the mixing valve delivered only a .1gpm difference in the two setups. The thing I took away from it is that the conclusion is that using PEX will not cause enough flow restriction to make the fixture not work as designed.
 
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Old 02-27-15, 05:54 PM
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hi Keith -

even though the test fixtures blended the hot and cold-water supplies differently, the total flow rates through the valves were 1.9 gpm for the PEX system and 2.0 gpm for the copper system. Therefore, the total flow for each pipe system through the test fixture was within an insignificant amount of 0.1 gpm.

I highlighted a part of their statement above, the differently seems significant to me Ė but it doesnít seem significant to them. The valves in the 2 setups are supposed to be identical- so why do they blend differently? The blend differential between the 2 seems pretty significant (to me anyway, lol).

What I donít understand is why 13% more hot flow is needed in the PEX setup vs. the copper setup to maintain the same constant temperature output at the shower valve. That seems backwards to me. I would think there would be more heat loss on the copper hot-supply pipe than on the PEX hot-supply pipe, thus requiring less flow from the PEX hot-supply pipe vs. the copper to maintain the constant temperature at the shower valve output Ė not more flow from the PEX hot-supply pipe.

Yet they claim the pressure balancing valves are the same in the two setups. That seems to me to indicate that either there is a greater heat loss in the PEX pipe than the copper thus requiring more hot flow from the PEX to maintain temperature, which doesnít make sense since copper has a greater thermal coefficient than plastic and should lose heat faster, or the 2 valves were in fact dissimilar in the 2 tests, which would then mean that the entire comparison test was not valid Ė I think, lol.

So Iím thinking the entire study is suspicious (but am I paranoid? lol)

Maybe Iíll shoot off an email and ask those guys (Iím sure they would love that lol).
 
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Old 02-27-15, 06:14 PM
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FYI gents the op has not responded back with his issue...

IMO chatter should be limited till the op posts back...
 
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Old 03-04-15, 07:41 AM
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Apologize guys. I had to go out for business trip and just came back.
So finally I figured out. Started working on it right after I came back and did the plumbing again with PEX and Copper to test the flow.
1. Its correct PEX or Copper should not make any difference in the water flow.
2. There was problem with valve and kohler would not agree there can be a problem, so I bought the new valve same Kohler K728 cheaper on Amazon. ( I could have changed the inside part - cartridge but it was almost just $20.00 less then whole valve.)
3. Both fittings (PEX and Copper) worked exactly fine and water pressure is great .
4. Well This is first time I am using PEX and its hell lot easier to work with and works great.
But somehow its a feeling that when I see copper some how feel good as its strong inside the walls and PEX feels like less safe. May be I will overcome this feeling over period of time.
 
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Old 03-04-15, 08:21 AM
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Thanks for the update, Glad you got it sorted. Don't worry aabout pex. When installed properly it is superior to cooper in many ways.
 
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Old 03-04-15, 08:28 AM
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Good news s2. But IMHO you should mail that valve to Kohler with a little nastygram in the box. Maybe they will hang their heads in shame and mail you a few bucks.


(I would do it even without an RMA)
 
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Old 03-04-15, 09:21 AM
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If you want to go back to Kohler, find their Customer Relations Department or whatever they call it and send your information to them. It is their job to keep customers happy and obviously you need support in that department. I have done this several times with legitimate problems that were not handled properly by the store or the help department and never been disappointed by their response. In fact, they want to hear from you.

Kohler is a big company and compensating you to improve the good will is something they already have a budget for.

Bud
 
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Old 03-04-15, 11:12 AM
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That's a good idea. I can tell them to test it and if it works keep it and if it doesn't give my money back since your rep did not believe me that its not working.
 
 

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