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Is 3/4" Pex necessary?

5K views 73 replies 20 participants last post by  Golden view 
#1 ·
I'm building this house that has very long runs.

125' from end to end.

My water supply will be roughly 50' and 75' away from the furthest fixtures...respectively.

My intention was to run a manifold system using copper manifolds with 1" inlets and soldered on 3/4" pex valve outlets.
(I found a couple made by Sioux Chief that fit the bill.)

Basically, each bathroom (two of them being the farthest points) and the kitchen (30') will have 3/4" pex supplies that branch as they arrive at the fixtures.

The Master Bath is obviously the most important, and is the 50' run.


Questions....
Am I overbuilding this thing?
Would 1/2" home runs be sufficient for speed of hot water to fixtures and pressure at fixtures?
Would the volume in 3/4" actually slow the delivery of hot water (from a Stiebel electric on demand)?

After a great thread years ago (by a plumber who is long gone) about Pex diameter, fittings, and pressure loss; I've been running 3/4" to everything with good results.

Just wondering what you experts think about this situation though.

Thanks in advance,
Jonathan
 
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#68 ·
FWIW, my brother built a fairly large house powered by solar. Pressure drops were a key consideration for efficiency.

The design solution was to use large pipes to bring the water to areas that needed it, then individual pipes from there to each fixture.

Rock solid, but an expensive way to go.
 
#69 ·
FWIW, my brother built a fairly large house powered by solar. Pressure drops were a key consideration for efficiency.



The design solution was to use large pipes to bring the water to areas that needed it, then individual pipes from there to each fixture.



Rock solid, but an expensive way to go.


How large?

3/4” mains (from manifold) to 1/2” branches would be more than sufficient from what I can tell.

Expensive?



Sent from my iPhone using Tapatalk
 
#70 ·
A manifold system can still experience pressure drop as additional fixtures are turned on, based on the limitations of the service line to the manifold.

A trunk system can perform just as well, but using a lot less pipe.

In my opinion the only two advantages of a manifold system are that you can turn off an individual line to replace a stop, and that any single fixture will get hot water faster, but the clock is reset to zero for each additional fixture, versus a trunk system which will have hot water at least part way to other fixtures.
 
#71 ·
Pex has a smaller ID but from a design perspective that is usually assumed to have similar flow to copper due to less fittings.

BRG, I think you have to weigh the benefits. If you want to supply a number of fixtures that may be used at the same time without a pressure drop, using a single feed, then the 3/4 is a better call. If you want faster hot water to certain locations, e.g. master bath shower, then consider running dedicated feeds to those locations. It costs more to plumb but it will provide hot water in half the time and pressure will be constant, assuming the supply can keep up with multiple demands.
 
#73 · (Edited)
RE: flow "killing" copper elbows, buy and USE long radius fittings, and deburr all pipe cuts internally.... And there is the old school of using one size larger "bushed" fittings to cut flow losses....

My final solution is a pumped recirculating pump that is motion sensor activated, and stops when the water reaches a set point, and has logic that locks it out for 30-45 minutes at time...

cheap hack: Fart fan wired with recirculating pump and 30-60 second timed relay? one way valves as needed to prevent reverse flows.

If you have 50 feet of 3/4" "hot" water line connected to a High Efficiency clothes washer, does it every get 'Hot' water when it uses water in 2-3 gallon gulps every 15-25 minutes?

would you want a 100 year house with 100 year old Pex or 100 year old Copper piping?

Is Pex mouse and Rat proof?
 
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