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Discuss PB versus Pex, something not quite right in the Fittings & Pipes area at

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  1. windycol

    windycol New Member

    I am converting a stone barn with 4 washrooms to fit and a remote boiler ( 3 Ph electric due to an abundance of solar power) I intended to fit a hot water loop system, however on aquiring the required PB barrier pipe (polyplumb) i find that the application notes for this product say under no circumstances should this be used for this type of installation.:thumbs_down: So not being one to take this lying down I started digging a hole! first i spoke to polypipe to ask why? they said it was due to the oxygen content of the hot water being constantly circulated would over time strip away the barrier layer??? This sounded a little off so decided to speak to WRAS and ask if this also applied to Pex? they couldn't comment however in the course of the conversation it became apparent that WRAS approval for polypipe was originally for cold water use and that the approval for hot water had been achieved by a work around using Bs 7291 part 1 2 or 3. The WRAS approval expired in august and to date, no application has been made for re-approval, for either cold water use or for hot water use which would require a lengthy testing.
    Apart from this though, My question/concern is that my understanding is that Pex is also approved under BS7291 part 1,2 or 3 and also would not be suitable under this for use in hot water loop circuits yet many suppliers of Pex and PB are saying Pex is o/k
  2. SimonG

    SimonG Trusted Plumber

    Rural barn? Plastic pipes and mice dont mix.

    Secondary returns not to be done in plastic. Manufacturers say no, so do at your own risk.
    • Like Like x 2
  3. snowhead

    snowhead Well-Known Member

    Manufacturers test to their own standards and industry standards.
    Their own may exceed Industry.

    If a manufacturer says it's OK for recirculating, then it must be.
    Who have you found that say it can be used.?


    All the above are part of the Plastic Pipes Group, say not suitable.
    Last edited: Sep 13, 2016
  4. Chalked

    Chalked Plumber GSR

    No pex or PB will allow circulated hot water. Only Uponor q&e is suitable.
    As above though, mice love pex and PB. Why not use copper?
  5. snowhead

    snowhead Well-Known Member

    From here;

    Uponor MLC & Secondary circulation.

    Secondary circulation is classified as a system that:

     Provides potable hot water
     Maintains a temperature in excess of 65°C
     Replenishes water used in outlet with fresh water (oxygenated water) .
     Is a pumped circulation system.

    If all four of the points are covered your system is classified as a secondary circulation system (or recirculation system). Plastic pipeworks manufactured under BS-7291-1/3 2010 cannot be used in secondary circulation applications. Uponor MLC pipe can be used in secondary circulation because it is manufactured under a different standard (BS EN ISO 21003-1 2008) also because of the aluminum layer within the pipework it has a higher tolerance than a standard PEX pipe system. Although there still should be appropriate water temperature control on the system to ensure the water temperature does not exceed 70°C as stated in our guidelines.
    • Like Like x 2
    Last edited: Sep 13, 2016
  6. oz-plumber

    oz-plumber Plumber

    Why is it that some of these pipe brands can be used for heating systems, circulating at the same or higher temperatures and not be a problem.

    As for Uponor pipe stating that the temperatures should not exceed 70 C, well that's barely above the temperature requirements for prevention of Legionella.

    Not sure what your regs state, but ours state, the circulation temperature should be a minimum of 65 C.

    I wouldn't use a product that gives the supplier a 'get out of gaol card' over a 5 C clause.
  7. snowhead

    snowhead Well-Known Member

    Heating systems cycle On /Off so the pipe isn't constantly at high temperatures, even in the UK


    Heating systems and fan coil installations where the water temperature does not continuously exceed 80oC, or momentarily exceed 95oC (no more than 100 hours a year), and maximum operating pressure of 10 bar. Also, the system must be installed with room and water temperature controls in accordance with the current Building Regulations Parts L1 (Energy – Dwellings) and L2 (Energy – Non Dwellings) for England and Wales, or an equivalent national standard for Scotland or Republic of Ireland.
     Hot water services installations where the water temperature
    does not continuously exceed 70oC, or momentarily exceed 95oC (no more than 100 hours a year), and maximum operating pressure of 10 bar.
  8. Masood

    Masood Guest

    Plus CH primary water will eventually de-aerate. It's oxygenated water that creates problems for plastic pipe...
  9. rpm

    rpm Trusted Plumber

    Having seen what small mice can do to plastic pipe I wouldn`t risk it.
  10. windycol

    windycol New Member

    Cos copper doesnt come in 50metre coils at 28mm diameter that's why!
  11. SimonG

    SimonG Trusted Plumber

    Your putting a 28mm secondary return in?
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    O God get a plumber in unless it's a swimming centre or a small hospital you won't need a src that big
  13. Chalked

    Chalked Plumber GSR

    Do what you like then! What do we know.?
    • Like Like x 2
  14. NickH

    NickH Active Member

    I've been led to believe that plastic is ok for a return loop provided the system isn't running continuously , ie it's on a timer so it's only running at intermittent times.
  15. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    No no only copper, q and e or mlcp
  16. windycol

    windycol New Member

    Abandoned secondary return, now going with straight delivery. Mice shouldn't pose a problem as the pipes will be in a dedicated insulated structure buried in the ground /concrete floors of the main building. I have never experience mice damage on any of the electrics/pipework i have dealt with over the last 30 years. I would think there would be less likelyhood in the countryside than an urban environment as field mice tend to be smaller than the normal domestic variety and don't struggle to find natural foods etc. With older town properties having timber joist floors I could imagine this might be an issue. Rats might be more of an issue in urban areas as it has been found that you are never more than 5 metre from one!

    This barn conversion is a total rebuild internally with solid floors and modern fully insulated structures above with attention being given to voids and cavities. so not envisaging a problem!
  17. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Depending on run / run off times of hot water you may need one
  18. Riley

    Riley Plumber GSR

    Thing is you've asked for help and gone with what you want anyway even when we're telling you from Our experience it's not a good idea, but you obviously know better
  19. windycol

    windycol New Member

    Sorry don't understand the point you are trying to make here, as because you have all advised that loop was not a good idea, i have reverted to a straight feed of the hot water to the bathrooms and not looping it back though for the life of me i cannot see that the effect on the pipework will be any greater in a direct feed than it would be in a controlled loop!
  20. Riley

    Riley Plumber GSR

    I was really making reference to the insistence on using plastic when you would be susceptible to wildlife. I have seen it loads of times in rural areas
  21. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    The reason we said no is the size doesn't need to be the same size as your main hot circuit

    And s lot once that length has cooled down you need to draw all the cold water off before you can get hot with a src this is minimal
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