Water Supply Line Size

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Brian Stokes

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Hey guys, I built my house in Winter of 2014. The plumber ran a 5/8" inside diameter Blue pex line 118' for my water supply. I have good pressure at the meter, 65 psi. I have the same at the outside hose bib until someone turns on the water at another source and it goes to pot. House is 2 story with 2 full bathrooms up and 2 down. Two showers cant run at the same time or the washing machine and a shower with decent pressure. If I replace it with a larger line would that solve the problem? iI so, What size line. I like the idea of PVC.

Thanks
 

Reach4

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One inch would give a big improvement. 1.25 inches would give a big improvement over inch. Some areas have codes for minimum size. If you are in such an area, it would be a good idea to meet the local requirements while you are making the change.

Here is a pipeline calculator for irrigation. I chose it because it is easier than some. http://irrigation.wsu.edu/Content/Calculators/General/Pipeline-Pressure-Loss.php
If you don't like that one, there are others.

Plug in your numbers of possible choices along with maybe 10 GPM. Compare the pressure drops calculated. The pressure drop is a function of cross sectional area, length and turbulence. With bigger pipe, you get less turbulence, so the gain is better than just the ratio of areas would imply.
 

Terry

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Four bathrooms should have been 1-1/4" water line from meter.
PVC would be fine, that or poly.

There are some charts at this link.
https://terrylove.com/watersize.htm

A four bath would be about 39 fixture units.

With distance, you have friction loss.
At 80 feet of distance with a 3/4" meter:
3/4" copper, 19 fixture units
1" copper, 36 fixture units
1-1/4" copper, 39 fixture units

At 200 feet:
3/4" copper, 11 fixture units
1" copper, 23 fixture units
1-1/4" copper, 39 fixture units

You can see how badly the 3/4" and the 1" fare with added distance.

pipe_size_2.jpg



pipe_size_1.jpg
 
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hj

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Poly is usually cts, (the o.d. dimension is 1/8" bigger), while PVC is ips, (the i.d. is the pipe size), so there is a big difference between their capacities.
 

Gary Swart

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It would appear you are confusing "pressure" with "flow". You could have a pipe the size of a soda straw and have 65 psi, but very little flow. Common misunderstanding. Heed the pros' advice above.
 

Brian Stokes

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Thanks guys, yes "flow" is the issue. I'm not sure how they ran lines to various rooms without pulling down the insulation in the crawl. Probably the most economical method. If I run 1-1/4 the 118' and then tie in to the smaller pex at the cut off in the crawl, the various showers will still be pulling off a 5/8 ID pex feeds. Will the additional volume in the supply to the house make that much difference in flow? Will I need to increase the feed size where the individual bathrooms tie in to see real results?
 

Gary Swart

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Your main supply line should be 1-1/4" or even 1-1/2". At the house reduce to 1/2". That's copper size, I don't know PEX sizing, but I think it's smaller than copper.
 

Jadnashua

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FWIW, pex (and a lot of copper) has a nominal ID. What is called 1/2" pex or copper has the same 5/8" OD, but because pex's tubing wall is much thicker, pex has less flow capacity than copper (smaller ID) for the same tubing size. 1/2" pex should provide all of the volume a single showerhead can use...it might start to get deficient if you wanted to run two at once, depending on the showerhead, the distance, and the number of fittings required. By feeding the dwelling with a big enough pipe, and if you then branch out intelligently, each fixture should be able to get adequate volume.

There's a known friction (resulting in pressure loss during flow) based on length, altitude changes, and fittings for both copper and pex tubing, so it's not all that hard to calculate both the volume and pressure available at the end. FWIW, when there's no flow, you should have the same pressure at all outlets (at the same elevation), but it will drop once you open the valve if there's not enough capacity for the demand. Water pressure will change a bit over 0.4#/foot of elevation change, which is why they pump stuff up into a tower so the pump doesn't have to run constantly in many cases, and still have pressure in the pipes.
 

Brian Stokes

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Thanks Again, Decided to call a master plumber I met at the building department to come out and look it over.
 

Brian Stokes

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OK, Master plumber says to increase the trunk lines to 1-1/4" pvc for more volume. $2,000. If improvement is not satisfactory then increase pipe size from meter. I have two main Trunk lines running parallel from the supply to the Master bath at the far end of the house, one hot, one cold. Main line comes in and has a spur off to the HWH then it returns to form the hot line. They both spur off to the laundry room, then Kitchen, then upstairs (2) bathrooms, then gust bath, then last the master bath at the end of lines.
I'm not a plumber but it seems if volume is the problem then maybe a big tank like 80 gallons and a booster pump my work? I hate to chop up my new pex lines and splice in PVC. Seems like a rig.
 

Reach4

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You have a pressure gauge. That can help you find what different parts of the system are losing. In particular, a pressure gauge would help you know how much pressure loss is in the feed from the street vs inside. Handy places to attach include laundry, water heater, and particularly the outside spigots. You did hook up to the outside spigot. What does that say when you were using the showers and producing the low pressure symptom? Often there is a spigot supplied from near where the water comes into the house. If that pressure from the street drops to 30 while you are running those showers, new piping inside can't help much, I would not think.

Does "trunk line" mean the lines from the house incoming and the WH output to the inputs to PEX manifolds, or what? Most people use more hot than cold water during a shower presuming that the water heater is not set very hot and the incoming water is cool. Maybe your Georgia cold water is not so cold. Anyway, if you are using much more hot than cold, you could turn up the hot so that the cold and hot pipes are carrying a more equal load. That would help the inside pressure drops, but it would not help the drop from the street.

It seems to me that making a rough line diagram of your plumbing, and taking pressure measurements at various points while running the water, would tell you where the major drops are.
 
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Your MP was correct, because a larger cross section area of pipes means more volume.

Ever try to breath through a drinking straw? All the lung pressure in the world won't help.

The size of the water heater tank is not going to help if you don't change your supply pipes, and a "booster pump" isn't going to deliver double the volume you expect. To get double volume, you need double cross section area of pipes.

In my neighborhood, the city water supply comes into the house in 3/4" copper, and the homeowner shut off reduces that to 1/2".

A neighbor with a large family solved your similar issue by tossing out all his 1/2" and re-piping his entire home with 3/4" copper.

I understand you have new PEX in your home, most people just accept and live with the complaints you are having now. Everyone knows not to run the washing machine when someone is in the shower, nor flush a toilet.

Since you want "more", you'll need "more" in pipes.

You may want to read this:
http://www.johnhearfield.com/Water/Water_in_pipes.htm
 

Terry

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It's volume and friction loss.
You can run the 1-1/4" PVC, or install a water storage tank there. There is no need for a pressure boost though since you already have 65 PSI
The booster is for those with low pressure.
 

Reach4

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There are booster pumps that could help if the incoming water pressure is where the big drop occurs. So lets say, for example, that you found that when you are taking your showers that the spigot that is near the house input shows ("to pot" =20 PSI). There are booster pumps that can boost the pressure. I remember reading a post from somebody who had such a pump, and was dismayed that he had to replace that pump every 3 years approximately. An investment in a new bigger supply from the street would be a nice quiet alternative to a booster and would last 100 years. So $400 or so plus installation to be repeated with the associated stress and effort every 3 years vs a big one-and-done expense.
 

Jadnashua

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The Copper Institute's recommendation on water velocity through piping is to not exceed 8fps on a cold water supply, or 5fps with hot. On a 3/4" copper pipe using hot water, that equates to about 8gpm, but it's only 4gpm with a 1/2" copper pipe. Pex is less because the ID is smaller, but they do allow the velocity to be higher. So, you really need to know how many gpm you need to supply at any one time to determine the size of the supply piping. THen, you need to account for friction based on the distance, and potential pressure loss if you're going uphill may affect things, too, at about 0.43#/foot elevation change.
 
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