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Old 07-21-2012, 11:33 PM   #1
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Manifold or loop


I'm redoing my plumbing from the basement and plan on using pex. I had heard of ways of using a water manifold or loop to keep the water pressure more constant. Currently the plumbing is like most old homes, a hack job or t's.

My entrance is only 1/2 and I cant seem to find a manifold that has an inlet for 1/2.

What would be the best way to keep the pressure constant?

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Old 07-22-2012, 12:44 AM   #2
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Manifold or loop


Either is better that the old way.
the manifold is probably the best but have a manifold with a loop,
Loop can be less expensive.
Sometimes a combination of the two.

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Old 07-22-2012, 04:14 AM   #3
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Manifold or loop


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Originally Posted by simonb View Post
I'm redoing my plumbing from the basement and plan on using pex. I had heard of ways of using a water manifold or loop to keep the water pressure more constant. Currently the plumbing is like most old homes, a hack job or t's.

My entrance is only 1/2 and I cant seem to find a manifold that has an inlet for 1/2.

What would be the best way to keep the pressure constant?
The best way to re-plumb a home for consistent water pressure to every fixture is to use the Home Run configuration. One manifold for cold at the source and one manifold for hot next to the water heater. Individual lines from the manifolds to each fixture. Google PEX Home Run and there is a lot of info available.

Assuming that you have a copper main line, there are many copper fittings to adapt 1/2 inch to whatever size input the PEX manifold requires. Your water heater should have 3/4 inch lines in/out so adapt the 3/4 inch output to suit the PEX manifold you get.

HRG
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Old 07-22-2012, 10:18 AM   #4
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Manifold or loop


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Originally Posted by Homerepairguy View Post
The best way to re-plumb a home for consistent water pressure to every fixture is to use the Home Run configuration. One manifold for cold at the source and one manifold for hot next to the water heater. Individual lines from the manifolds to each fixture. Google PEX Home Run and there is a lot of info available.

Assuming that you have a copper main line, there are many copper fittings to adapt 1/2 inch to whatever size input the PEX manifold requires. Your water heater should have 3/4 inch lines in/out so adapt the 3/4 inch output to suit the PEX manifold you get.

HRG
Thats prety much what i wanted to do with the manifold. The problem is that everything, including the hot water in and out are all 1/2. I was under the impresion that you couldnt go from 1/2 to 3/4 because you will loose pressure.
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Old 07-22-2012, 12:56 PM   #5
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Manifold or loop


You're only looking at half the picture. You're correct that you'll see a very slight pressure loss from the 1/2 to 3/4 expansion. However, you'll lose far less pressure to pipe friction by having 3/4" pipe. I played around with a few online calculators, and for flows >= 0.25 gal/min and up will regain the pressure loss if you replace at least 1 foot of 1/2" pipe with 3/4" pipe. The calculators started to break down under 0.25 gal/min so I couldn't go any lower. Given that at full blast you're normally in the range of 0.5 gal/min for a sink to 2.5 gal/min for a low flow shower, going lower is probably just a waste of time.
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Old 07-22-2012, 01:10 PM   #6
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Manifold or loop


It may be worthwhile to buy a $16 GPM/PSI meter in addition to doing the calcs.

Your incoming GPM @ min PSI (=5?) is 16 or less and static pressure is between 40 and 80 PSI, with minimum flow occurring at 5 PSI or so.
Knowing the "pump curve" at your water inlet may help
http://www.google.com/imgres?imgurl=...QEwAA&dur=4053
and you can plot this using your $16 meter.

Using max and min pipe lengths, max and min desired PSI/GPM values and different pipe sizes, work out some permutations and see what combinations seem promising, on paper.

It's all non-linear exponential equations and you may need to use a graphical method to solve for this, or cut-and-try using a spreadsheet.

Last edited by Yoyizit; 07-22-2012 at 01:13 PM.
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Old 07-22-2012, 02:53 PM   #7
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Manifold or loop


So from what I can understand, I can use the manifolds that are 3/4 inlet and 1/2 out, I just will have to use an adapter on the manifolds to go from 1/2 to 3/4.

I have a washroom on my second floor that already has plumbing isntalled and is all tied in to a single hot and a single cold that I will not change. Will this have any effect on using manifolds? Keep in mind only one fixture in teh washroom is usualy being used at once.
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Old 07-22-2012, 04:22 PM   #8
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Manifold or loop


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Originally Posted by simonb View Post
Thats prety much what i wanted to do with the manifold. The problem is that everything, including the hot water in and out are all 1/2. I was under the impresion that you couldnt go from 1/2 to 3/4 because you will loose pressure.
The important factor is water flow. The fixtures that need higher water flow are the tub spout and shower head. Water flow is decreased by frictional losses, the longer the line length. But that can be overcome by using larger diameter lines.

Flow restricted shower heads are limited to 2.5 gpm. If you remove the flow restrictor, say you get 3.5 gpm out of the shower head.

Your 1/2 inch supply line will probably put out "at least" 7 gpm with your water pressure reducing valve (aka pressure regulator) set to 60 psi. So even if you transition the 1/2 inch supply line to a 3/4 or 1 inch manifold input, you should still have "at least" 7 gpm available to feed your hot and cold lines. Then running two 1/2 inch lines (hot and cold) to your tub/shower should give you the 3.5 gpm you need at the shower head.

Also, as this link says:

"People sometimes tell us that it doesn't make sense to change the piping inside the house until the pipe from the street to the house is replaced. We've just shown that that is not true. Increasing any piece of pipe in the entire system will improve the water supply. The more pipe we change, the better it gets."
http://www.managemylife.com/mmh/ques...ect-water-flow

Finally, note that the Uponor PEX system gives higher water flow rates for a given tubing size. This is because the Uponor system uses the expansion method for joints which means the ID of the fittings are about the same ID as the tubing. In crimp/cinch PEX systems, the ID of the fittings are smaller than the ID of the tubing which restricts water flow more than the Uponor PEX system. --- If you're concerned about water flow rates, I would definitely go with the Uponor/Wirsbo PEX system. In addition to better water flow rates, the Uponor fittings create less turbulence than the crimp/cinch fittings.

HRG
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Old 07-22-2012, 05:03 PM   #9
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Manifold or loop


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Originally Posted by simonb View Post
I'm redoing my plumbing from the basement
Here's what you're up against
http://www2.iccsafe.org/states/virgi...g%20System.pdf

Tedious, but it can be done.

On top of this is your requirement for constant PSI. . .perhaps you mean constant GPM?


Last edited by Yoyizit; 07-22-2012 at 05:19 PM.
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