First install of custom shower - thoughts on my plan (3/4 PEX from 1/2 copper)

[xyzz]

hey all,

As a DIYer i've done a bunch of small plumbing jobs over the years, but this will be my first custom shower. After reading a bunch online (mostly this site) - i think i have come up with a plan and just wanted to see what your thoughts are before I go ahead with it.


I have 1/2 copper lines coming in. I havent measured water pressure in my new house - but I can say it is very good - better than any other place I've lived .

I have an overhead shower, a handeld shower, 3 body sprays and 3 volume controls. The basic idea is that im using 3/4 pex as much as i can so i dont restrict flow. I'm using 1/2 pex where i have to (only at the end of the line when attached to a fixture - this is because i can only find 1/2 female drop ears with 1/2 pex attachements)

See attached image - ive done my best with MS paint on a laptop without a mouse


thanks in advance.


edit: just wanted to add - the line that goes to the hand shower, goes directly to the hand shower and is not part of the loop it passes over (its obvious but should have made that clear in the diagram)

 

[Jadnashua]

First, you need to add up the specified volume/minute of each item that will be on at the same time.

If you want to abide by the recommendations of the Copper Institute, on hot water supplies, you should not plan to require more than a velocity of 5fps...with a 1/2" copper pipe, that equates to 4gpm. Throw in that you'd be mixing that with at least some cold, and with 1/2" lines, you might get that up to about 6gpm, as you'd probably never get more than about 75:25 ratio of hot:cold (maybe in the winter - depends on the setting of the WH and how cold the incoming water is). Most 1/2" supply valves top out about that 6gpm, too. A 3/4" valve, fed from a 1/2" supply (copper - 3/4" pex is about the same volume as 1/2" copper) won't buy you much except expense. If you can feed it with 3/4" copper all the way, it would nearly double the volume available. Exceeding the Copper Institute recommendations can lead to excessive flow noise and literal wearing of the pipe. FWIW, pex can support slightly higher flow rates, but combined with the smaller ID for the equivalent sized pipe, comes out about the same gpm volumes without undue pressure losses.

It's useful to know your actual incoming water pressure. Plumbing codes call for it to not exceed 80psi. If it does, they require it to be regulated to that value or lower. For the combination of all desired shower heads to perform as designed, you need at LEAST the volume of water they require, and more doesn't buy you as much. As long as you can provide them with the desired volume, you should be happy...if not, the perceived strength of the spray will decrease. You also need to take into account the size of your water heater and supply system (a drain water heat recovery system can help extend the useful volume of shower water by preheating the cold so you use less hot).

 

[Sponsor]

 

[xyzz]

First, you need to add up the specified volume/minute of each item that will be on at the same time.

If you want to abide by the recommendations of the Copper Institute, on hot water supplies, you should not plan to require more than a velocity of 5fps...with a 1/2" copper pipe, that equates to 4gpm. Throw in that you'd be mixing that with at least some cold, and with 1/2" lines, you might get that up to about 6gpm, as you'd probably never get more than about 75:25 ratio of hot:cold (maybe in the winter - depends on the setting of the WH and how cold the incoming water is). Most 1/2" supply valves top out about that 6gpm, too. A 3/4" valve, fed from a 1/2" supply (copper - 3/4" pex is about the same volume as 1/2" copper) won't buy you much except expense. If you can feed it with 3/4" copper all the way, it would nearly double the volume available. Exceeding the Copper Institute recommendations can lead to excessive flow noise and literal wearing of the pipe. FWIW, pex can support slightly higher flow rates, but combined with the smaller ID for the equivalent sized pipe, comes out about the same gpm volumes without undue pressure losses.

It's useful to know your actual incoming water pressure. Plumbing codes call for it to not exceed 80psi. If it does, they require it to be regulated to that value or lower. For the combination of all desired shower heads to perform as designed, you need at LEAST the volume of water they require, and more doesn't buy you as much. As long as you can provide them with the desired volume, you should be happy...if not, the perceived strength of the spray will decrease. You also need to take into account the size of your water heater and supply system (a drain water heat recovery system can help extend the useful volume of shower water by preheating the cold so you use less hot).

thanks for the reply - lots of good info there. I was able to get this shower system for a really low price, so I will be installing what I have - rather than calculating everything out first and then selecting the right equipment. This will mainly be my shower. I plan on having only the shower on , or the 3 body sprays, or the handheld shower. I may, on occasion, have the overhead shower on AND the 3 body sprays... if im not with what is happening, i will simply turn one of them off. I just want to make sure there are no red flags in my plumbing plan that i may not be aware of. (or if it could be optimized in any way)

thanks!

 

[xyzz]

any comments on the plan? specifically, im wondering if i am upsizing to 3/4" and downsizing to 1/2" in the most efficient spots

 

[hj]

Nice loop, however it is COMPLETELY useless and not necessary.

 

[xyzz]

im using pex, and am just trying to eliminate bottlenecks (1/2 pex fittings).. not worth it?

 

[Jadnashua]

The ID of 3/4" pex is about the same as the ID of 1/2" copper...so, to maintain the maximum flow with minimum pressure losses, the 3/4" pex has the advantage when extending 1/2" copper. 1/2" pex can easily feed one shower head, and maybe two body sprays, but it would, I think, start to show problems if you got that to three body sprays, depending on the specific ones you have.

 

[Reach4]

The ID of 3/4" pex is about the same as the ID of 1/2" copper.

The inside area of 3/4 PEX pipe is 56% larger than for type L 1/2 inch copper. However the ID of that PEX pipe is only 25% larger.

Yes, the PEX fittings ID is considerably smaller.

 

[Reach4]

this is because i can only find 1/2 female drop ears with 1/2 pex attachements)

https://www.pexuniverse.com/3-4-pex-x-1-2-drop-ear-elbow is one, but there may be others.

It will take longer for hot water to arrive through 3/4 inch PEX, if that matters to you.

 

[Jadnashua]

https://www.huduser.gov/portal/publications/pex_design_guide.pdf

https://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf

The ID of 1/2" type L copper is 0.545" according to the copper institute while the ID of 1/2" pex is 0.475" and 3/4" pex is 0.671".

0.671-0.545 = 0.126" or about 23% larger in ID. Then, throw in the pex fitting that goes inside of the pipe verses copper's fitting on the outside of the pipe, and the overall differences, depending on the velocity and the lengths involved, 3/4" coppers flow rate is even closer to that of 1/2" copper. I was talking about the ID....yes, the area of the pex opening is larger, but again, the fittings do affect the overall flow and pressure. Using 1/2" pex verses the 1/2" copper, the area of the opening is in the ratio of .074 vs .056 so the copper is larger by a factor of 32% or if you look at it the other way, 1/2" pex has about 76% of the area (again, not counting fittings). Comparing 1/2" L copper to 3/4" pex, you get .074 verses .113 or about 53% more, but again, once you take into account the fact the fittings on pex are decreasing the ID, 3/4" pex will give you about the same volume/flow as 1/2" copper. 1/2" pex will be much less than 1/2" copper. So, if you want to not create flow restrictions, 3/4" pex will approximate 1/2" copper without losses, where 1/2" pex will show a decrease in performance.

Now, if you happen to use type M verses L, the copper gets even larger in the ID at 0.569 or .081 verses .113, or the 3/4" pex is about 40% larger in area not accounting for the fittings.

Bottom line, the ID of the effective pex is smaller than the ID of the tubing, and when all things are considered, if you want to maximize the flow from a 1/2" copper pipe, use 3/4" pex, not 1/2" pex.

Depending on where you make the 1/2" copper to pex conversion, the differences in the total volume and thus how long it takes to flush it out may be insignificant. I got the impression that rather than running new copper, you're converting to pex in the bathroom, so the amount of pex will be minimal, and thus, if there were a few seconds difference in flushing the lines, I'd be surprised.

 

[Reach4]

The ID of 1/2" type L copper is 0.545" according to the copper institute while the ID of 1/2" pex is 0.475" and 3/4" pex is 0.671".

0.681 according to https://www.pexuniverse.com/pex-tubing-technical-specs, but I agree other documents say 0.671. So that still makes the ID of the 3/4 PEX 23% larger, and the area 52% larger than the 1/2 copper.

Bottom line, the ID of the effective pex is smaller than the ID of the tubing, and when all things are considered, if you want to maximize the flow from a 1/2" copper pipe, use 3/4" pex, not 1/2" pex.

The bottom line is that "The ID of 3/4" pex is about the same as the ID of 1/2" copper" is wrong. You can try to baffle us with distraction, but the ID of 3/4 PEX is significantly larger than 1/2 inch copper.