Forum Title: Home Run System with Manifolds
I'm building a new house and am planning on doing a Pex "Home Run" system with individual water lines serving each fixture in the house. It's a small house with a centrally located water heater, short runs, only a few sweeping turns and very efficient low flow fixtures. It seems like an ideal situation for 3/8" pex branches allowing for quick delivery of hot water with minimal wastage. I've already calculated the friction losses in each 3/8" pipe run based on the flow rates, length of piping, number of turns, resistance in fittings and head losses and they're quite low. I have no worries about pressure and flow using this size pipe. I'm trying to figure out exactly how I'm going to terminate the 3/8" pex at each fixture since I'm very limited in my selection for 3/8" parts. After looking through the parts catalogue is see two options (Each option uses a sink as an example): Option 1 flow path: Start at 3/8" crimp fitting branch in the manifold Continuous pex run without fittings all the way to stud cavity behind sink 3/8" crimp fitting to 1/2" copper stubout 1/2" sweat stop valve to 3/8" male thread braided flexible supply line to threaded connection on faucet Option 1 means I can go with a simpler manifold without valves on each individual branch. There's also a rigid copper pipe making the transition through the drywall which I prefer. I don't like the copper to pex transition inside the wall, especially since a few of these connections will be in an exterior wall (on the warm side of 12" of insulation, however). Option 2 flow path: Start at 3/8" crimp fitting on branch valve on manifold Continuous run of 3/8" pex without fittings all the way to stud cavity behind sink poke the pex pipe through the drywall and up towards the faucet connection use a 3/8" crimp fitting to female thread adapter and install on male threaded faucet connections Option 2 will have several disadvantages like requiring valves on each manifold branch since there won't be any shutoffs at the fixture end. It will require fewer transitions and no buried connections but the pex will be exposed and vulnerable outside the drywall running all the way to the faucet. The piece that adapts the pex to the faucet has female threads that are made of plastic. What are your thoughts?
Category: Plumber Post By: ASHLEY PETERSON (Philadelphia, PA), 07/29/2016

Hi Frodo, Thanks for your reply. My plan was to have one valve on each run; either at the valve or at the manifold. What I'm simply trying to avoid is the redundancy of having one of these fancy manifold systems with the individual branch valves when there's already a stop valve at each fixture. Just my personal opinion, but one main shutoff valve in the entire house is all that's needed for the two times per decade you might have to use it. I take it you don't have a problem with the pex to copper transition inside the wall cavity? I can't agree with some people's automatic dismissal of 3/8 pex. The only reasons I've ever heard against 3/8 were anecdotal or gut feelings. When you actually get out the charts, tables, pens, paper and calculators and actually crunch some real numbers - 3/8 pex is fine for a lot of modern applications. If you're not concerned about water usage or willing to plan out the plumbing layout and do the calculations beforehand then sure, 1/2 pex is a great one-size fits all solution.

- HARVEY STEELE (Plantation, FL), 09/10/2017

Quote: Originally Posted by RockinOnWater Hi Frodo, Thanks for your reply. My plan was to have one valve on each run; either at the valve or at the manifold. What I'm simply trying to avoid is the redundancy of having one of these fancy manifold systems with the individual branch valves when there's already a stop valve at each fixture. Just my personal opinion, but one main shutoff valve in the entire house is all that's needed for the two times per decade you might have to use it. I take it you don't have a problem with the pex to copper transition inside the wall cavity? I can't agree with some people's automatic dismissal of 3/8 pex. The only reasons I've ever heard against 3/8 were anecdotal or gut feelings. When you actually get out the charts, tables, pens, paper and calculators and actually crunch some real numbers - 3/8 pex is fine for a lot of modern applications. If you're not concerned about water usage or willing to plan out the plumbing layout and do the calculations beforehand then sure, 1/2 pex is a great one-size fits all solution. LOL..... being a plumber, I like high volume of water, if water usage or conservation is a concern, then simply do not open the valve all the way. If you are fine with 3/8'' and low volume ,then i am thrilled as a brown bear with a honey comb. I gave you some links that show manifolds without the valves. I would not buy the manblock for $400.00 when I could use a copper one for $40.00. cause I am cheap. NO, i do not have a problem with crimp pex in the wall. as long as it is done correctly and is not shark bite or some other BS push on

- DEBRA ADAMS (Independence, MO), 09/21/2017

code requires a valve. your options are 1 at the manifold or 1 at the fixture. myself, i prefer 1 valve at the manifold for tubs, and outside hose bibs and for sinks and toilets one under the fixture. caution..... you do not want to use a sweat valve on the copper stub out. the stub out can become very hot and melt the pex. use a compression valve if you stub out pex. it will be floppy, look like hellhttp://www.supplyhouse.com/Crimp-Sty...ifolds-1826000http://www.supplyhouse.com/Matco-Nor...Stop-Lead-Freehttp://www.supplyhouse.com/pex/contr...%20stub%20outs i would not use 3/8'' pex, i would use 1/2'' http://screencast.com/t/NVUpUnSrdPzZ

- TINA SULLIVAN (Euclid, OH), 09/24/2017

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