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Please help with boiler/unvented cylinder choice

Discussion in 'Plumbing and Central Heating' started by RickyLee53, 19 Sep 2013.

  1. RickyLee53

    RickyLee53

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    Hello,

    I have a 4 bed 2 bathroom house. However have a very large bath, 400litres. And 2 large showers.
    Only 16 rads, 2 towel rails. Most of the house has aircon which also heats when required (and is arguably more efficient)

    I have a static pressure of 3.5bar. And a flow rate of around 30l per minute. (however I have laid 32mm MDPE upto the road, and I'm currently waiting for the waterboard to upgrade the lead from the edge of my property to the stopcock. I don't know how much this will improve the flow but i'm hoping a lot!)

    I have looked at system store boilers from recommendation on here some time ago. However the drawback is it has to fit in a tall unit in my kitchen. 590 approx by 590 by 1700mm.

    Option 1.

    System store Glow worm 170sxi

    I think massively underspec'd, but was recommended on here previously.

    Cheapest and easiest by far.

    Option 2

    Install 250litre indirect unvented in the cellar. Height is the issue 1740mm.
    This wouldn't give me enough hot water to completely fill the bath I don't think. Reheat time is 27 minutes but it would only have around 8 at 30lpm.

    Vaillant Ecotec 37 boiler. The cylinder is 20kw, so that only leaves 17kw for central heating for the rest of the house.

    This is underspec'd IMO but a plumber local recommend this and said it would be ok.
    Cheap, around £2000 plus controls.

    Option 3.

    2 x 210 cylinders, plenty of stored hot water however reheat will require 36kw!
    Pottering 46kw boiler, again only leaving 10kw for CH when reheating.
    Around £3000.

    The huge worry for me with this is balancing the cylinders and still having the rad's going cold when the water is being reheated, or doesn't this really matter if setup correctly?

    Option 4.

    2 x 210l cylinders
    2 x boilers, maybe even a combi and a system.

    Thanks for any help, i'm open to any other suggestions.
     
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  3. dcawkwell

    dcawkwell

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    2 bathrooms

    Glow worm ultra power
    a cross between unvented and combi you will never run out of hot water as it falls back to combi mode should the tank run out of hot water.
    Boiler and tank all in the nice one box and will outperform a 300 litre unvented cylinder.
    Sorted job done.

    It should fit in a kitchen cupboard but check.


    Two fairly small combi boilers would also do it easily.
     
  4. RickyLee53

    RickyLee53

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    Hello,

    I can make that fit and did have that as my first option.

    However reading the literature it says it only actually stores 120litres of hot water and has a reheat time of 10 minutes. Hence the name 170sxi (I think) as it gives 170litres at 30lpm approx. This certainly wouldn't be enough to fill my bath.
    I understand it also has a combi type feature that gives 12lpm approx. But i'm not sure how this works. Does it always run the combi for the first 12 litres per minute then use the tank for the other 18? Which ever way it just doesn't seem large enough for the bath.

    [​IMG]
     
  5. RickyLee53

    RickyLee53

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    dcawkwell;

    I didn't really think about 2 combi's. How would you go about the balancing of them though. Fitment might be an issue though. And still i'd be looking around 24litres per minute hot water even with a fairly large combi.
     
  6. rich4nancy

    rich4nancy

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    Are you not intending on mixing any cold into your bath water ? Also the bath may well have a capacity of 400 litres, but surely not when 2 people are in it? Water displacement? (The pic looks like a 2 person bath btw?)
     
  7. RickyLee53

    RickyLee53

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    Hello,

    Yes, i'd say approx 1/3 hot water. This means around 250 litres approx hot water.

    It is 2 person. Only normally use for 1 or the kids. It is actually 460 litres to just below the overflow. So you would need approx 400 litres to be full. I don't want to leave the rest of the house with no hot water for 20 minutes because somebody has been in the bath.
     
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  9. rich4nancy

    rich4nancy

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    I think you may have your maths wrong. Filling the bath 1/3 with hot water which you calculate to be 250l then your bath would be 750 litres? Still without any water displacement.
     
  10. cozzmic

    cozzmic

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  11. RickyLee53

    RickyLee53

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    Sorry 1/3 cold water is what was meant.
     
  12. RickyLee53

    RickyLee53

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    That seems like a good idea.

    I wish there were some intelligent controls which would allow you to use a combi in conjunction with a cylinder.

    I have also though, would I be better using 2 boilers. One in the cellar next to the cylinder, and a second in the utility.

     
  13. cozzmic

    cozzmic

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    You could use a combi and split the heating with motorised valves to heat the cylinder seperately from the heating and the combi to do one of the bathrooms.
     
  14. CBF

    CBF

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    i wouldn't go the combi route unless you want to wait at least 25 mins to fill the bath
     
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