Am I going to loose a water pressure in the shower head? iBox

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Drewski123, Dec 10, 2011.

  1. Drewski123

    Drewski123 New Member

    Messages:
    47
    Location:
    Seattle
    I am thinking of switching to PEX from a copper in my current bathroom renovation. This question pertains to a possible pressure loss in a shower head.
    Here is what I am planning to do. I will be using Grohe iBox Universal Plus Rough for shower/tub (two function only). The supply pipes will be 3/4", the pipe that runs out from the iBox that will connect the tub spout will also be 3/4", and the shower pipe extending from the iBox will be 1/2". In a remote area, about 5 feet away from the shower I am thinking of installing a manifold with valves which are going to be 1/2" PEX Valves (all copper). So, here is the issue I have. If the PEX running from the manifold is 1/2" with an additional coupling 1/2" to 3/4" down the road (so I can connect the pipe with the IBox 3/4" supporting supply pipes), will I loose a pressure in the shower head?

    Thanks for your help on this,

    [​IMG]
    Last edited by a moderator: May 8, 2012
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    22,266
    Location:
    New England
    You lose pressure if the fixture is capable of using more water than is supplied, sort of like a finger over the end of a hose. With one showerhead, 1/2" pex would work. If you're trying to fill the tub as well, either don't use pex, or go larger. 1/2" pex is about the same ID as 3/8" copper. 3/4" pex is closer the 1/2" copper. With a 3/4" valve (expensive), I don't know why you'd want to throttle it down with 1/2" pex.
  3. Drewski123

    Drewski123 New Member

    Messages:
    47
    Location:
    Seattle
    Jim, I am little bit confused with your answear. I am attaching a couple of drawings, Option1 and Option 2 of what I am planning to do. I hope this will help.

    Attached Files:

  4. mtcummins

    mtcummins In the Trades

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    380
    Location:
    Pittsburgh PA
    Pex doesn't necessarily reduce flow rates. It can or not, depending on the install. The fittings have a smaller ID than copper, but that restriction is usually more than made up for in the smoother flow through the pex (especially as copper ages), far fewer fittings, much smoother, longer turns, etc.

    I keep hearing people say that 1/2" pex is about equal to 3/8" copper... I'd like to see some numbers to justify this. 1/2" Pex is typically .475" I.D., which is quite larger than 3/8". Code usually allows equal sizing of Pex b/c the benefits of it compensate for the smaller I.D. fittings, so it generally gives about equal performance in the system.

    In a home run system for a house, pex will generally outperform equivalent sized copper. In short runs with lots of fittings, copper will outperform pex. Its not as simple as people tend to make it out to be.

    The biggest concern in your setup is reducing to 1/2" and then going back up to 3/4". Regardless of pipe material, that is where you're going to lose your flow rate.

    Pex vs copper is not going to make much difference in your setup, I'd pick the system you are most comfortable with and go with that. Just don't reduce pipe size and take it back up, that bottleneck will be a problem.
  5. mtcummins

    mtcummins In the Trades

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    Location:
    Pittsburgh PA
    Your last post came up while I was typing. Definitely use the open manifolds with 3/4" Pex supplies to the shower. You will not get proper performance if you reduce and then increase the pipe diameter.
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
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    Location:
    Land of Cheese
    95% of all houses in the U.S. have the shower and tub plumbed in 1/2" I.D. pipe. 3/4" is completely unnecessary for a shower with a single head.

    If you are running PEX, then you will want to run 3/4 PEX, because it has a smaller inside diameter than copper.
  7. mtcummins

    mtcummins In the Trades

    Messages:
    380
    Location:
    Pittsburgh PA
    yeah, the 3/4" isn't necessary for the shower head, the flow rate on the head will restrict the flow either way so it won't matter. I think the reason the rough-ins are 3/4 is so the tub will fill faster, so you might as well go with it and take advantage of the setup. You already have 3/4" line there. But yes, the shower (assuming it is a 2.5 GPM or less head of today's standard), will be equal pressure with either.
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    You paid a lot more for a 3/4" valve, so, run 3/4" lines to it. If you want the max flow rate to fill the tub, you'd want 1" pex all the way back to the supply. But, as said, if it's only one showerhead, 1/2" pex would keep the pressure up as the pipe is capable of more volume than that (typically in the order of 5-6gpm, depending on your pressure). Since a 3/4" valve is typically capable of 14-16gpm, why fill the tub less than half as fast?

    Depending on the pex fastener used, it further reduces the ID. But, depending on how many fittings are used, assuming it is short enough, it acts more like a venturi, and momentarily flows faster through the restriction, and only affects the volume slightly. But, each time it does that, it increases the total restrictions, and the flow available, even if only a little...lots of them do add up.
    Last edited: Dec 10, 2011
  9. mtcummins

    mtcummins In the Trades

    Messages:
    380
    Location:
    Pittsburgh PA
    There have been numerous tests conducted with a trunk and branch copper system next to an equivalent (same size lines in same places, but pex system uses less fittings) trunk and branch pex system (which is the least efficient method of running pex), and the performance was virtually equal. Far fewer fittings and gentle curves instead of sharp 90s, as well as much smoother interior walls, make up for the smaller IDs. This is why they're allowed to be installed at equivalent sizing.

    In a home run Pex system, which is the norm in new construction, you will get greater flow rates and pressures at fixtures than with a traditional trunk and branch copper system. Add to that the pressure balancing, lower cost, resistance to freeze bursts, lack of pinhole leaks, speed of install (to get the project/build done faster), ability to isolate a line for repairs w/o effecting rest of house, and other benefits, and Pex becomes much more attractive.
  10. Drewski123

    Drewski123 New Member

    Messages:
    47
    Location:
    Seattle
    Thanks everyone. One more question I have, would you consider Wirsbo's EP Flow-Through Roll-Out Multi-Port Tee or you would prefer a copper PEX manifold? If a copper manifold is preferred, would the Sioux Chief brand work with Wirsbo's AquaPEX?

    Additionally, I am also planning to add a tankless electric water heater to the bathroom area someday in the future. And, on my next project (kitchen renovation) I will also plan on adding tankless water heater there too, which will also serve washer and the utility sink (additional remote manifold will be installed there too). To summarize, I will have 2 separate manifolds in my house (single story, 1 bathroom with a basement, will possibly add a small bathrrom in the basement right underneath the existing bathroom which I am currently working on), and two separate tankless water heaters. I would appreciate any comments on this too.
  11. mtcummins

    mtcummins In the Trades

    Messages:
    380
    Location:
    Pittsburgh PA
    I personally use copper manifolds and just crimp on my own shutoffs. I think the plastic manifolds feel cheap, and though they're probably of fine quality, I don't feel like paying what they charge for them when they feel so cheap to me. That said, I'm sure they're faster and easier to install, so plumbers probably prefer them in that regard. Also, I've never installed one, I just chose to use the copper ones from the beginning and never looked back.

    Buy one bigger than you need, if it's in an area (basement) where there's any chance you could tap off of it again (say to add another outdoor spigot, or whatever), and just put little short pex stubs with caps in them on the ones you don't use. The small extra cost is well worth it, you'd be surprised how often you find the need for another line. I bought mine with extra hot and cold ports from my initial design, and then plans changed, and I'm now already out of cold ports. Now I'll have to buy another 4-6 port open manifold and tap it into the main line, which is just annoying.

    Edit: I should have said to put a shutoff on the ports you don't use, then a short piece with a cap. Otherwise you'll be shutting down your whole house, or at least that manifold, to be able to add the new line on. Yes you could just leave the shutoff in the off position, but is it worth the chance of it accidentally getting opened?
    Last edited: Dec 10, 2011
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
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    Location:
    Cave Creek, Arizona
    quote; With a 3/4" valve (expensive), I don't know why you'd want to throttle it down with 1/2" pex.

    He did NOT have a choice. The I-Box is ONLY made in 3/4", but they furnish 3/4"x1/2" brass bushings to use with 1/2" piping.
    1. Unless they have merged, the I-Box is Hansgrohe
    2. You cannot just pipe down the spout and up to the shower head. You either need volume control, on/off, valves on BOTH pipes, or use a twin-ell, (which ALWAYS has 1/2" inlets), at the diverter spout. Either way, the pipe from the valve to the spout can be anything you desire. It will have NO effect on the shower head.

    [​IMG]
    Last edited by a moderator: May 8, 2012
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,048
    Location:
    Cave Creek, Arizona
    Pex

    To have an i.d. of .475, the wall thickness would have to be slightly more than 1/16", and PEX walls are THICKER than that. An insert fitting measures .4" o.d., while 3/8" type "L" copper has an actual I.D. of .43", which calculates to LARGER than 1/2" PEX.
    Last edited: Dec 11, 2011
  14. mtcummins

    mtcummins In the Trades

    Messages:
    380
    Location:
    Pittsburgh PA
    I'm just quoting the manufacturer's stated I.D.

    You can't compare the I.D. of the fitting to the I.D. of the tubing, so that comparison is irrelevant. The fitting being smaller creates only a slight resistance, the piping a much larger one. They're not equivalent. That said, lots of Pex fittings (which would generally indicate a poor installation) will cause a lower flow rate.

    I've never denied that Pex has a smaller I.D., but I think this is blown out of proportion, especially when it has been demonstrated that it works equivalently when installed in the same manner as Copper, which is the least effective method to install Pex. With a home-run system, you will have better performance than with copper in general. A very short run from the manifold may be slightly lower flow rate than an equivalent copper line, until the copper line gets all scaled up inside, then the Pex will be ahead there too.
  15. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
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    Location:
    Land of Cheese
    I guess the question is really more about who's information do you want to believe? The PEX manufacturers or the plumbers who have experience installing it?

    From what I have seen in new construction, where a house would have had 3/4" copper, it now gets 1" PEX. All the PEX gets upsized- this is well known. It was the same way with CPVC. They way things are built these days, it would not be common practice if is were not needed.

    Unless you are using Wirsbo fittings, the I.D. of many fittings is pretty close to half the tubing size. This is the reason they want you to avoid using fittings wherever it is possible.

    And I don't know what kind of water they have in Pittsburgh, but there is no scale in any copper here. I see 50 year old galvanized pipe that is clean as a whistle on the inside. The only reason any plumber switched to PEX around here is because the copper prices went through the roof.

    People don't want plastic houses, but they do want to be able to pay for them.
  16. mtcummins

    mtcummins In the Trades

    Messages:
    380
    Location:
    Pittsburgh PA
    I have a good bit of experience installing Pex, and mostly replacing/repairing copper systems (never installed a whole house with it, but have done repairs and small changes many times, and cut out old copper to replace either the whole system or a significant portion with pex). I have a home run system in my house, 3/4" supply to the manifolds in the basement, 1/2" supply lines from there to every fixture. The water pressure and flow rate is far superior to the old 3/4" trunk and 1/2" branch copper system.

    Many others will tell you the same thing. Copper corrodes/gets mineral deposits, etc unless you have perfectly balanced water, which not many people do. If you are lucky enough to have that, good for you, but that is not the norm. Even w/o corrosion, pex flows better, with less resistance along its surface area. This generally makes up for the smaller ID. Most people will have reduced performance of their copper systems over time due to mineral build-ups etc.

    Maybe some people are doing the larger size as common practice, but it is totally unnecessary. The fixtures restrict flow to less than the capacity of 1/2" pex in almost every case anyway, so upsizing is just wasting money and drilling larger holes in your structure for no real reason. A tub filler would benefit from 3/4", as it is basically unrestricted. A spigot might, depending on the sillcock you have and the hose you're using. A washer might, depending on its internals, fill up faster w/ 3/4". Most other appliances/fixtures will not benefit.

    CPVC has basically all the fittings problems of copper, so a smaller ID combined with that might be cause to consider upsizing. I hate the stuff, so I don't have any real experience with it to comment intelligently on that one. I think that the Pex oversizing is just hangover thinking from CPVC, not based in reality.
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