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Replacing radiators for underfloor heating.

Discussion in 'Plumbing and Central Heating' started by chris765, 27 Dec 2013.

  1. chris765

    chris765

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    Hi,

    I am seeking a bit of guidance please. We have moved into a property that requires renovating.

    We had a new combi boiler installed last year and now we are looking to replace most of our downstairs radiators with underfloor heating.
    When I say most, there are 2 in our utility room that now would be difficult to replace with underfloor heating as the room is finished - so we need to keep them :-/.

    Downstairs is open plan so we have no requirement for separate zones.
    The area is approx 5650mmx9950mm and will be half concrete and half timber floor. The joints are at 400mm so all underfloor pipework will be at 200 centres.

    So what would I like to know?

    Ultimately we just want to have one programmer/stat (we currently have a CM927 wireless). To increase the temperature at the moment we just increase it on the CM927, we don't want to have to do it on more stats if possible? Ideally we would like the underfloor heating to act as if it were a radiator with a TRV but guess this isn't possible because the pump needs to know when to run.
    We have TRVs on all the upstairs and 2 downstairs radiators.

    Because of the 2 radiators downstairs I assume I need to run another flow and return from the boiler, so theres a zone valve on the radiator flow and a zone valve on the UFH flow? Does this new flow and return need to be 22mm.

    What is the maximum zone size, am I able to achieve 55m^2 in one run which maintains a constant heat, or will I get a cold spot towards the end of the run?

    Is there any systems anyone is able to recommend for this?

    Please see attached drawing. I forgot to note that the left third of the house is a ground floor extension. The floor is uneven, hence the reason it's being concrete filled, the original house has a timber floor which is in good order.


    Many thanks for reading.
    Chris.


     
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  3. chris765

    chris765

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    With some further research and thought;

    I am never going to be calling for radiator or underfloor heating separately. Would this then negate the need for the zone valves, the manifold could run from the same flow and return?

    Does the UFH pump/manifold need a permanent live, could I take this from the Switch live from the stat, so the pump/manifold only has power when the heating is being called for, and then would switch in if the UFH isn't up to temperature? Just like a radiator with its TRV?

    Thanks.
     
  4. RickMoore

    RickMoore

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    Underfloor heating will never work properly when though of or treated like a radiator. It usually takes a correctly designed system a good couple of hours to get to temperature. If you zone it with the radiators it will never work properly.
     
  5. dcawkwell

    dcawkwell

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    Stick with radiators.
    Underfloor heating more trouble than it is worth.
     
  6. mogget

    mogget

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  7. chris765

    chris765

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    Thanks all for your advice.

    I'm an electrician so it's just understanding the water element.

    I can now see that the UFH needs to be treated differently to a radiator. I will look into this further, which another zone valve etc.
    Thanks.
     
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  9. RickMoore

    RickMoore

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    Rubbish. Done properly it's very good, the problem is that few installers and fewer users really understand it.
    Ive got underfloor in my bathroom and youngests bedroom. It works spot on and keeps the rooms very comfortable. Ive installed it for alot of customers and without exception they have been very pleased. Ive even improved a few badly installed systems with marked improvement.
    Anything is more trouble that its worth when its thrown in by a monkey.
     
  10. I find the biggest problem with underfloor heating is people not understanding how it operates and what controls to use to make the system operate correctly.
     
  11. Tipper

    Tipper

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    You need to separate the circuits completely.

    Idealy install a low loss header directly from the boiler then add individual pumped and controlled circuits from the header, ie, separate ufh and rad circuits each with its own pump and thermostat.

    That is the only way it will work.

    I have two ufh manifolds with pumps and one rad circuit with its own pump running perfectly. Each has its own thermostat/s.!
     
  12. chris765

    chris765

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    Hi all and thanks for your replies.

    So I will go down the route of installing an extra Flow, having all the radiators on a different zone than the underfloor heating.
    Both will have a motorised zone valve on their flow and a pump each (will the manifold pump alone be suitable for the UFH or do I need another?).

    Both will have their own prog/stat so will be treated differently.

    Do I need to run another return for the UFH or can I use the same return as the radiators, this of course if I go down the route of not using a Low loss header.

    thanks
     
  13. RickMoore

    RickMoore

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    The boilers pump will handle the rads and between boiler and ufh manifold. The ufh manifold pump will pump water around the ufh circuits. Zone valves control weather either or both the rads and ufh get heat.

    Be aware that the ufh may suffer when the boiler is producing alot of hotwater. This may or may not be an issue.

    Best would be to t a new flow and return feed to the manifold as close as possible to the boiler.
     
  14. Norcon

    Norcon

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    You might want to fit a rad in the living area.
    In spring or autumn there will be times when firing up the ufh is just not necessary.
    But still a slight chill in the living area during evening time so the rad gives a quick response.

    Might sound as though its defeating the purpose of ufh but its common practise in new builds round here.
    Just zone it along with the utility room. Turn it off when you don't want it operating. Fit an extra manifold and use full runs to each rad.
    So no joints under floors.

    Well its your choice. At the very least leave pipes in place and the option is there.
     
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