Pex (Uponor) efficiency/flow and manifold Qs...going from 3/4" to 1"?

9 years ago

I am planning a "temporarily permanent" re-do of my under-slab copper plumbing to pex. specifically Uponor. Some background...

I just had another slab leak and I'm tired of it. I plan on doing a major remodel of the house in the near future and part of that plan was to homerun pex. Now that this slab leak happened, I want a quick re-do for now so I don't have to worry about the next shoe dropping. My solution is to use a hybrid system: Uponor Logic for cold and homerun for hot.

(I'm sure some of you are thinking: Why doesn't he just homerun the cold now? Well, I just don't want a mile of pex snaking every-which-way up in the attic until I organize things up there. And I don't have to worry about the need to purge residual cold water. I want to homerun the hot to minimize the wait time of purging cold water in the far bathroom. If I use a 3/4" trunk for hot, it's over twice the volume of the 1/2" homerun that I have to bleed out. So I only have to wait, instead of waiting and waiting.)

My house is @ 2350 square feet and single story. The length (front to back) of the house is @ 80 feet. Water service is 1" copper from the street and it reduces to 3/4" copper through the studs in the garage for about 21 +/- feet to the inside wall in the garage where it splits for cold and hot and submarines through the footing. (Tankless heater was installed up in the garage attic so the feed line first goes up to the tankless then back down through the footing.) Both the hot and cold trunks are 3/4" copper.

Static water pressure at the front hose bid right by the connection point to the water service line is 56 +/- psi. We're on a gravity feed.

My temporarily permanent solution is to run cold using the Uponor Logic system and to homerun the hot: a hybrid.

Cold trunk will be 3/4" pex that runs the length of the house and Uponor EP Flow-Through manifolds with 1/2" ports. There probably will be 4 manifolds in this spine.

For hot, I plan on using a 3/4" manifold with 1/2" ports (not valved, for now) to homerun each fixture.

My questions...finally.

1. For the HOT, allowing for extra runs/fixtures, I would want about 16 ports to homerun. Assuming that there is a manifold with 16 ports (which there isn't from Uponor), what would give the best flow to fixtures after the tankless:

- one 3/4" manifold with 16 ports;

- two 3/4" 8-port manifolds in an inline configuration with the second manifold capped;

- two 3/4" 8-port manifolds teeing off the 3/4" line from the tankless;

- two 3/4" 8-port manifolds teeing off the 3/4" line from the tankless, then connect the two manifolds using elbows/fittings and pex to form a loop?

I don't know much about pressure equalization and fluid dynamics and such that could/would have an effect with any of the above configurations.

2. Are manifolds designed to be unidirectional? In other words, is a 1" flow-through manifold with a 1" inlet and a 3/4" outlet and twelve 1/2" ports designed internally in such a way that, if I use the 3/4" outlet as an inlet, there are structures/baffles or whatever in the manifold that would create turbulence because water is flowing against the grain and prevent efficient distribution within the manifold to the ports? Or is the manifold just an empty space of air and completely reversible?

2 a. If you can't run the above manifold in reverse, how would I affect the efficiency and dynamics of distribution and flow if I transition the 3/4" out of the tankless to 1"?

3. For the cold line using Uponor Logic, if I transition the 3/4" copper to 1" pex instead of 3/4" as the spine, any bad effects?

4. Is a 1/2" line really enough for bathtubs and hose bibs?

Any help, suggestions, recommendations, and critiques would be appreciated.

Thanx

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Comments (3)

Vith
9 years ago
last modified: 9 years ago
Main line pressure would probably be higher than other pressures, so if you take another line and put it as an intake where it is meant to be an outlet at the manifold, the higher pressure of the main will push against it. Manifolds are designed to be unidirectional due to pressure pushing the water in one direction, there is nothing inside the manifold to make water go anywhere, its just an area to balance the pressure in all the lines.

If your main is 3/4" then going up to 1" wont make a difference. It may actually drop pressure.

1/2 line is enough for a bathtub.

The less ports you have the less wasting water waiting for hot water. What I did at my place is two main manifolds and ran a 1/2 hot and cold line to each room and that line just branches to the fixtures at the room, I have not had a problem with pressure. I have 4 hot (kitchen, laundry, bath 1, bath 2) and 5 cold runs (kitchen, laundry, bath 1, bath 2, outside faucets). There are various ways to do it, you could have two main manifolds one for hot one for cold which go to rooms and branch there, or you could have main sized lines going to each room and an accessible manifold there which supplies each fixture. I don't recommend long runs of pex from a manifold to each fixture, lots of water wasted waiting for hot and lot of extra water lines increasing chance of failures or punctures. I know that is what they push as a product but a bunch of extra water lines is just inefficient for hot and risky for cold.
executech79
Original Author
9 years ago
I'm afraid I wasn't clear enough with my manifold query and it led you to misread what I was thinking of doing... Allow me to clarify.

I'm not planning to use both the 1" inlet and 3/4" outlet of the manifold as inlets. I may use the 3/4" outlet as the inlet and the 1" inlet as the outlet to continue a 1" trunk line. I'll be reversing the flow of its advertised direction. When I checked with Uponor, they told me that it was designed to be used with the 1" as the inlet and 3/4" as the outlet so it wasn't *recommended* in reverse. They didn't endorse what I'm contemplating, but other than toeing the company line and stating that it's "not recommended," they didn't believe there would an issue. But the tech didn't know if there were fins/spoilers/baffles/pitches/etc. in the interior of the manifold or the ports that were engineered with water flowing in the recommended direction. I don't believe there'll be an issue, but I was hoping to get a confirmation from an actual application.

As to the continuing 1" line that's downstream from the manifold, I can't foresee any issues to subsequent flow-through, inline manifolds along the way and their 1/2" ports, but I'm not absolutely certain since the velocity would slow going from 3/4" to 1". I was hoping to get some opinions and real-world experiences on that, too.

Between the additional volume in the 1" compared to the 3/4" and unlikelihood of having more than three fixtures on those 1/2" lines being used simultaneously, I don't anticipate exceeding the supply rate of the 3/4", so, in my mind, I'm thinking that I shouldn't have any pressure balancing issues either with the 1".

I agree that the less pex I run, the better. So other than the 1" or 3/4" question from the above paragraphs, I'm set on one "continuous" trunk for COLD with several, inline, multi-port manifolds along the way with 1/2" lines to the fixtures. My hall bathroom, powder room, and laundry room are clustered together so that minimizes excessive 1/2" runs. The master bathroom and kitchen are to the back, far-left and back, far-right, respectively, from the longitudinal center of the house, so I can't escape having some semi-long 1/2" lines to the kitchen unless I tee a 1" or 3/4" branch line, which I'm not inclined to do.

For the HOT, I'm still leaning toward 1/2" homerun lines, especially for the master bathroom and kitchen, to minimize wait times and residual waste. I ***may*** do a 3/4" line to the central cluster and use a local manifold set-up to minimize 1/2" spaghettification: it's still under advisement.

What's your opinion on pressure balancing loops? It's like the chupacabra; some say yes and others say no. I'm trying to figure out if I should(n"t) for the HOT's multi-manifold set-up. My inclination is to loop it since it can't hurt, unless there are specific cons against it.

Thanx for your response, Vith. I was beginning to worry that my query would suffer a slow and virginal demise.

J
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Vith
9 years ago
Having the large main line and using manifolds will keep your pressures good. I have not done a loop before so I cannot give an opinion on it. I don't think using the 3/4" as an inlet and the 1" as an outlet will cause any real problems.

Pex (Uponor) efficiency/flow and manifold Qs...going from 3/4" to 1"?

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Vith

executech79
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Pex (Uponor) efficiency/flow and manifold Qs...going from 3/4" to 1"?

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Vith

executech79Original Author

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executech79
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