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Thread: PEX Manifold System Request

  1. #1
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    Default PEX Manifold System Request

    I am a desing - build custom builder.

    We have been using pex systems and manifold distribution.

    We typically operate each fixture (H&C) with H&C manifold valves.

    One of our design - build clients has asked that valve controls (both hot and cold) be limited in scope to one room (bathroom - kitchen - etc.) as compared to each fixture.

    Why he wants to do this - I do not know, but have a planning meeting on Wednesday of this week and want some professional opinion - info to share.

    I would appreciate some response - opinion - cost cpomparrison as possible.

    4200 SF LA home, 2 tankless water heaters, 2 pex manifold systems (WH locations), 5 full baths, 2 laundry rooms, kitchen. See attached Floor Plan - BR 2-3-4 Guest Quarters Pex System 1- all other areas Pex System 2.
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  2. #2
    Plumber jimbo's Avatar
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    What is the rating of the two tankless? With 5 baths, 2 laundry rooms....they better be big!

  3. #3
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    What is the rating of the two tankless? With 5 baths, 2 laundry rooms....they better be big!

    A family home with guest rooms for the grown children - not living at home - normally just 2 adults living in the home.

    Holidays - family gatherings - may be the max use of facilities.

    We were told by one of our plumbers that a Rinni Model 5RL75E (VB2528WD) would work. I have planned but not done discovery work on the model yet.

    I am all ears.....

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    That model can raise 7.5g of water per minute 40-degrees; use less water, it can raise it more, try to use more, it can raise it less. Physical facts. Now, depending on your local cold water inlet temperature, that might be fine. I find it a little misleading, as the thing is preset for 120-degree water, and few people have 80-degree inlet water, which is the only way it can provide the stated volume of water at the specified temperatures. Also, it won't turn on until you are requesting at least 0.4gpm, and when, say you have a lavatory faucet turned on to warm to wash your hands, you may never get any hot to mix in, as the total flow is not enough to trigger the tankless to turn on. Turn it to all hot, and it's too hot to wash your hands, so you turn it back down, and (often, not always) it will turn off, so you end up with cold again.

    So, how cold is the incoming water in the dead of winter? How much do you think you might want at any one simultaneous use? Things like the dishwasher want fairly hot water, but some have a built-in heater (costs more to activate, since it is electrical). You may not need hot to wash clothes often, but that can max things out. Say your incoming winter water temp is 40-degrees (mine actually has been measured at 33!), it would only get it up to 80-degrees (40-degree rise), which is a far cry from hot. Showerheads are spec'ed to dispense no more than 2.5gpm. So, if three were on, you'd be maxed out, and they may not be warm enough, depending on the incoming water temp...then, say someone turns something else on, and the temp would drop even more. Consider installing thermostatically controlled shower valves if you go this way, at least then, it won't be you moving the handle to keep or get the water at your desired temp.

    Depends on your needs and desires. You can install two of them, in series, and then improve the rise, but that can get quite expensive.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5
    Moderator & Master Plumber hj's Avatar
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    If you plan on using "manifold valves" for the installation, they are NOT large enough to supply an entire room. I do not even like the idea of manifold valves, because when a faucet has to be repaired, and the valve is not a the fixture, then I will turn off the entire house rather than use a manifold valve, with its attendant possibility of failure/leaking.
    Licensed residential and commercial plumber

  6. #6
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    Thanks Jim. Many have asked, and we have installed "point of use", but this may be the first time we have installed whole house tankless. If seems you have provided the discovery I targeted.

    Do you, or any other readers have recommended tankless whole house units providing less risk and better service?

  7. #7
    General Engineering Contractor ballvalve's Avatar
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    2 people in a 4200 square foot house. Better get an ankle GPS to locate each other. I have had endless problems with tankless rigs and don't trust any of them now.

    Valves on in floor heating zones, but with a shut off valve at each fixture, whats the point of shutting off a room?

  8. #8
    DIY Junior Member Widdershins's Avatar
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    Quote Originally Posted by ballvalve View Post
    2 people in a 4200 square foot house. Better get an ankle GPS to locate each other. I have had endless problems with tankless rigs and don't trust any of them now.

    Valves on in floor heating zones, but with a shut off valve at each fixture, whats the point of shutting off a room?

    Zone valves for individual bathrooms or wings of the home are an anticipatory measure -- Meaning they likely anticipate problems down the road and want to negate the need to shut down and drain the entire house for a minor repair. This is especially true in homes with multiple H/W return lines that would need to be purged of air and carefully balanced again after the water is turned back on.

    As for having shut-offs at each fixture -- That isn't always the case with in-wall lavatory faucets, tub/shower valves, roman tub faucets or even pillar mounted valve sets for free standing tubs.

  9. #9
    General Engineering Contractor ballvalve's Avatar
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    Since they have endless sums of money, just buy a huge pile of manifolds... that no one will ever use and when they try to will discover that the valves are calcium closed forever.

    And you can design shut offs for all those fixtures mentioned, out and then back into the wall. Perhaps a manifold under every sink for that room.

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