Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Manabloc Supplying Cold Water Non-Oxygen Barrier Pex Mix & Radiant Heating

cloves Member Posts: 16
Hi everyone,

I have a closed radiant heating system and I had an question about pex tubing that popped up. Our water main is getting fed into a water filter and then into a 30 port manabloc. The manabloc will provide our domestic water for all of our fixtures. The manabloc has a cold feed through at the bottom which is made to feed the water heater. We will be running 3/4 barrier pex to the water heater and 3/4 barrier pex back to the hot intake on the manabloc. The 1/2 feeds for the fixture will be non-barrier pex.

My question is will the non barrier pex on the cold side from the fixtures send oxygen molecules into the the cold feed through supply of the manabloc? This of course would introduce oxygen into the radiant heating system which would be a bad thing.


  • Snowmelt
    Snowmelt Member Posts: 1,404

    The answer to your question is yes, that's why we call it a closed loop system. Also we have to get the oxygen out by way of air seperator.

    Unless you want a open loop system where the circulator is no bronze or stainless steel. Along with the expansion tank is made for potable water.
  • Zman
    Zman Member Posts: 7,542

    It is ok to use non barrier for domestic water. The system is oxygenated anyway.

    I don't see the radiant system in your drawing. It should be isolated by a backflow preventer and use barrier tubing.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SWEI
    SWEI Member Posts: 7,356
    Manabloc and DHW recirc

    Just in case you haven't read the fine print, Viega does not approve of DHW recirc through the Manablock.  Too bad IMO -- it would be such an easy hookup and would bring hot water right to where it is needed.
  • Weezbo
    Weezbo Member Posts: 6,232
    edited May 2014
    that sounds like a very bad idea.

    i have seen it done , hooked up to a munchkin cannot say much in a positive way for that lash up . PLS fittings from wirsbo would have been a better choice lashed to a flatplate ,if realestate was the deciding factor in the arrangement .

    A buffer tank off the plate might even salvage that . rust needs O and heat to accelerate ,so, you have to consider that in you selection of parts and pieces.water has plenty of O as it is...think about it for a min.

    i am off t help out a bit moving an old bucket of heat converted from coal to oil,

    for a tank and new boiler and new pex lines for the domestic .

    The three hundred gallon tank he has rusted from the inside out and no amount of screws with rubber washers can call back the decay over time. : (

    maybe the thing to do is look long term in your future , that may help . especially if you would like to or have to sell it one day.

    i hope all goes well.

    *~//: )

    and helps in some small way.

    this was a radiant heating system that i had seen run thru the maniblock ...

    long time back i was interested in using a wirsbo block that is built in pieces to do about the same thing for heating.. then , when the guy said no thats not quite what it is supposed to be used for , ...... i bagged the idea , then when i considered using a different lash up for domestic with a recirc line he wasn't good with that idea either.

    so , recirc lines thru the maniblock are not a good idea for heat or domestic.

    with domestic non barrier pex is what we use to be certain for the most part , some times i use Red Rehau barrier pipe for recirc or and hot water lines.
  • fixerDIYupper
    fixerDIYupper Member Posts: 8
    Yea, sounds like a bad idea. Not really a closed system for heating. I wouldn't mix porta water with heating system. get a separate manifold for the closed system, and use PAP instead of O2 barrier.
  • jbimmerle
    jbimmerle Member Posts: 1
    edited August 2016
    Hi all. Sorry to resurrect such an old thread but I had a similar question that is a variation of Cloves original question. I'm planning to have something similar done but have one of the 1/2" cold ports off my 30-port manabloc supply the Weil McLain boiler which in turn feeds the heater water to three separate zones. The water in these zones circulates back through the boiler when a heating call is made but never enters back into the manifold (the manabloc is only used for supplying all other plumbing fixtures in the house).

    Would this limit (I doubt it would eliminate) the introduction of oxygen into the "closed" system? Or would a better approach be to have a separate line branch off from the main (before the water filter and similar to what is done for my external hose bibs) and not have it use the manabloc at all? Everything would be fed to the burner with hePex - including the main line that supplies the hose bibs as well.

    Thanks in advance for the help.