PEX Plumbing / Repiping Layout & Installation Issues

I've been doing extensive web research and reading many of the excellent posts here (thanks to all) and have become absolutely sold on
PEX (no connections/joints behind walls) for my pipe replacement system, especially given the challenges of re-running pipes through this large masonry house.
As a background to some of the following questions, allow me to explain
the basic configuration of the home. The house is a two-story concrete/stucco structure with, unusual for Florida homes, a full attic
and a full basement/garage. This arrangement, I surmise, will afford some advantages for access/work space, as the entire upper floor is accessible from the attic, and the entire lower floor from the basement. There is, also, an HVAC/cable chase that runs in a straight shot from the attic to basement.
The main house feed is a 3/4" line, which comes into the house in the basement at ceiling level. The water heater is located on the second floor of the home, not the basement (flood zone) or first floor.
My current thinking, if possible and feasible, is to try to have one master manifold arrangement next to the water heater and to feed all appliances with homeruns from that manifold. In other words, I'd run the 3/4" house feed up the chase to the attic and over to the manifold,
and the water-heater run and return would be immediately adjacent. Then, I'd drop service lines down the second-floor walls to fixtures on
that level and run similar homeruns for first-floor fixtures back down the chase to the basement and across the basement ceiling and up through floor to first-floor fixtures.
I had considered using a secondary manifold in the basement, but after reading herein about hot-water delivery times and volumes, it seemed counterproductive to pump 3/4" of hot water all the way from the second
floor, through the attic, to the basement and more efficient to deliver
exact line sizes directly from the second floor master manifold to individual fixtures, based on their specific needs. An added benefit would be that all shutoff controls would be located in a single place.
In terms of fixtures, proposed line size, and estimated distance from the intended manifold location, they are as follows:
1st Floor: 3 bathroom sinks, 3/8", 30' 1 tub, 1/2", 25' 1 shower, 1/2", 25' 2 toilets, 3/8", 25' 1 bar sink, 3/8", 60' 1 kitchen sink, 3/8", 60' 1 dishwasher, 3/8", 60' 1 refrigerator icemaker, 1/4", 60'
2nd Floor: 1 bathroom sink, 3/8", 15' 1 tub, 1/2", 15' 2 showers, 1/2", 15' 1 toilet, 3/8", 15' 1 laundry room washer, 1/2", 30' 2 bathroom sinks, 3/8", 50' 1 shower, 1/2", 50' 1 toilet, 3/8", 50'
I would most appreciate it if anyone with plumbing, especially PEX, experience could comment on the above layout's suitability, given distances and line sizes.
A few ancillary questions:
1) Since the reason for doing this project is pinholes in copper, I was
proposing to use all-plastic fittings, versus brass. Good idea?
2) Is it necessary or advisable to insulate hot-water lines? If so, is
there any manner to do that, which allows the lines to be pulled through walls after being insulated?
3) Incidentally, anybody know whether Florida code permits fixture shutoffs to be located at the manifold, or must I have redundant shutoffs at the fixture sites?
4) Crimps (Vanguard) versus expanders Uponor/Wirsbo)? Any pros/cons? Reliability? Is PEX-A of significant benefit versus PEX-B for a residential water application?
Appreciate comments to above and any other pertinent advice.
Thanks in advance to all.
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tacker wrote:

I would use at least 1/2 everywhere and 3/4 for the main line to the distribution manifold. For less heat loss insulate all the hot water lines you can, espically around the HW tank
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tacker wrote:

I also am planning a PEX re-pipe (1930 2 story in SoCal) so I've been considering the same questions for a while. My house seems somewhat smaller than yours so my runs will be shorter.
I settled on Wirsbo expander system rather than the crimp tool. I even bought the hand expander (yeah I know my hand will get tired but I only have 36 connections to make)
I was (am) torn on the plastic vs brass but am leaning towards brass fittings we don't have the water / pin hole problems here.
I think PEX-A vs PEX-B is just a matter of the crosslink process. Again I'm going to use Wirsbo PEX.
Independent of code I'm thinking of fixture shutoffs for convenience in an "emergency" rather than me having to stumble down into the "basement / ultitty vault). Plus I'm used to having fixture shutoffs.
I asked Wirsbo if they had a modeling program for residential fresh water layouts; they don't,. But they sent me some ref tables with pressure drops per tube size & run length. My laptop crashed since then but I'm pretty sure I've got them on my backup disk.
If you're interested I can find them & send them to you.
Based on a quick look at the tables when I got them I pretty much decided to got with 1/2" everywhere. The pressure drops for 3/8" & 1/4" seemed too high.
I didn't think that any material saving was worth the extra hassle of having a bunch of different size tube & fittings; plus my expander only has heads for 1/2, 3/4 & 1"
Again my run lengths are shorter than yours but 50 ft of 1/2" tube will deliver hot water in ~30 secs at 1 gpm.............good enough for me since in my previous house w/ 40+ year galv I had to wait 2 minutes!
The secondary manifold might make sense if you put the hot water pump on a timer & only pump during hours of potential hot water use; 3/4 tube to manifold, 1/2" return to water heater.
I'm thinking about stealing the hot water for the dishwasher off the kitchen sink hot feed & saving a run. Same thing for the laudry room sink / washer. This can be done with 1/2" runs over 3/8" runs
Insulation of the hot water runs depends........... how cold is the environment through which the tubes run?
In SoCal, not that important, plus in my house a lot of the runs will be up through interior walls
Also the thermal conductivity of copper is about 800x higher than PEX so PEX is kinda insulated already. I know I can hold a piece of PEX dispensing hot water where copper will burn me :)
I don't have any brilliant idea for insulation
Pulling the PEX though mansonry walls makes me a little nervous wrt to scuffing the PEX.
cheers Bob
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The Wirsbo attachment system does seem elegant.

Given that having my metal pipes eaten is how I got here, i think I'll go 100% plastic.

I'd love to get your tables, if possible.
You might find useful information and diagrams for planning at: http://www.houseneeds.com/shop/plumbing/pexplumbing/vanguard/pexmanifoldsbuypage.htm

I was only considering the 3/8" to shorten time for hot water at kitchen sink, which has longest run. The manuals say 3/8" is sufficient. Anybody doubt that advice?

Florida. Insulation to keep pipes from heating house for more A/C load.

Sounds like insulation not a big factor.

House is masonry, but interior pulls are through drywall and studs.

Thanks for your reply.
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Insulate wall cavitys with PEX using expanding foam.
For a dishasher I have thought about installing a tempering valve on the hot water tank. set tank to 140 for dishwasher only, tempoering valve would drop temp to 120 for everywhere else/
this would save the electricity for the dishwasher water heater and gve us a slight increase in the amount of hot water availble too for showering etc
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I have a honest question in your research are there any cases of rodents ( rats) chewing threw PEX. I have heard it's happened but have never read anything about it myself.( just hear say) What caused the pine holes in the copper or at the joints?

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Have not heard, personally, of any instances of rodent problems with PEX. I certainly don't anticipate that problem in my house, and the rats have other much more tasty pickings around here, anyway. :-)
In Florida, pinholes in copper pipe are near epidemic. I believe, although nobody knows for 100% sure, that the problem arises from some chemical reaction between the water in Southwest Florida and the copper pipe. The frequency is higher at elbows, but straights are not immune either. The fact that Florida's building code has a less stringent standard (as I am told) for copper pipe probably doesn't help either.
In any case, a water distribution system with no copper or metallic parts and individually-valved homeruns from a central manifold to each outlet, containing not a single behind-wall joint, sounds like the perfect system for this area. Frankly, for any area.
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