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advise on low loss header

Discussion in 'Plumbing and Central Heating' started by Zehroni, 2 Oct 2021.

  1. Zehroni

    Zehroni

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    i built an extension and upgraded my main house heating by installing all underfloor heating. And I am in a process of replacing my old boiler combi(Worcester 28cdi, see pic) to new Worcester 8000 style 35kw system boiler and 250L Megaflo unvented cylinder. there is only one small radiator in the main family bathroom in the whole system. The rest are all underfloor heating, both upstairs and downstairs. there are there manifolds in the house; one for the main house upstairs, one for the main house downstairs and one for the extension (for both floors down stairs and up stairs). Each of these manifolds consists of 6 zones , see pic for one of them.

    I have been inviting local gas engineers for quote to replace the old system with new one and I am getting very confused and conflict messages as to weather a low loss header needs to be fitted into the new system. some say you need it, other say you do not need it, because although you have 3 manifolds (i.e. 3 plumbs), but all underfloor heating which they will run on low heat and hence the demand on the boiler will not be as high.

    any advise please whether I need a low loss header or not and why.
     

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  3. muggles

    muggles

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    For starters it's highly unlikely that you need a 35kW boiler, unless the floor area of your home is around 500-700 square metres. Do a heat loss calculation on www.heat-engineer.com to find out what size you actually need. Doing this will also better inform you as to whether you need a header or not - they're usually used on very large systems where the boiler's own pump can't provide the flow rate required for the system. Some form of separation may be desirable to account for the different flow rates between the UFH and what the boiler wants, but a header may not be the best solution. More system info needed, starting with that heat loss...
     
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  4. Zehroni

    Zehroni

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    the average area of the main house and the extension is 250 square meters. the Worcester 8000 style 35kw system was recommended by the first engineer who came around to provide a a quote and verified by others as well . However, when I checked Worcester website, it does also recommend it for large properties. the loss calculation is attached. can someone please let me know what size of boiler I need.
     

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  5. picasso

    picasso

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    A lot depends on level of insulation, windows (double glazed, single glazed, window area ect) did you try the link provided my muggles ?
     
  6. Zehroni

    Zehroni

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    yes i did, the calculation is attached in my previous reply, can't you see it
     
  7. picasso

    picasso

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    Something isn't right, more than one engineer has quoted a 35kw boiler and your calculations are less than 9kws , your heat load is probably nearer the 9 than the 35 but need more info.
     
  8. muggles

    muggles

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    Your calculation shows that you need 9kW, so 35kW is massively oversized
     
  9. Zehroni

    Zehroni

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    the calculation might be wrong, I only entered few parameters correct but the rest I did not understands (particularly the UV values) so just gust them, is there and instructions to show mw how to use the heat loss calculations?
     
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  11. muggles

    muggles

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    You shouldn't need to guess them, there are drop-down menus so you can select various building materials appropriate to your home. Did you use the paid one for £12 (more work but more accurate) or the free one? Worth using the paid one really to get the best result. If you go around guessing things you don't know then you'll always end up with the wrong result
     
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  12. Zehroni

    Zehroni

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    I used the free version. but still I do not know what to select. for example

    U Value Roof/Ceiling Glazing (W/m2K) . I do not have glazing in my roof. it is a normal pitched roof with 3000mm mineral insulation but all the options refer to glazing or U values which do not know what it is.
     
  13. muggles

    muggles

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    U values are insulation values. Further down under "N° of Roof Glazing" you can select zero, which will cause the calculator to ignore whatever value you might have entered in the box above, but you don't have to answer the first question about roof glazing if it's not relevant.

    If your total floor area is 250m² and the property is well insulated, the 9kW figure might not be too far out. I'd have gone for around 12-15kW on a rough back-of-an-envelope guesstimate. Either way, 35kW is massively oversized
     
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  14. dilalio

    dilalio

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    OP... Be careful what floor covering you use over the UFH. The TOG value of the floor will massively affect the MW-AT.
     
  15. Zehroni

    Zehroni

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    is it safe to calculate the heat loss from the under floor heating CAD design, see attached, if so then, the total output heat from the 3 manifolds is approximately 15kw. add another 1kw for the small radiator in the main family bathroom would make it 16kw.
    if the above assumptions are corrected then a system boiler of 20kw would be more than sufficient. Hence, can someone please help with the blow

    1. recommendation for a boiler
    2. do I still need a low loos header. some of the gas engineer who came around recommended it, some not, few never heard of it.
     

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  16. dilalio

    dilalio

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    You're asking for far more than is within the scope of this forum. We can advise but not do the research for you. You either learn how to do it yourself or pay for someone to come in and do it for you. If your contractors can't do this, find one who can and be prepared to pay extra for the survey and assessment, before works even begin.
     
  17. Zehroni

    Zehroni

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    I understand this is an open free forum and I am entitled to share the knowledge and benefit from other people experience. Therefore, i am not asking you to do the search for me. I am directing my question to whoever can positively and politely help.
     
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