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Cold water supply design

Discussion in 'Plumbing and Central Heating' started by Cael Mills, 9 Nov 2015.

  1. Cael Mills

    Cael Mills

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    Hi All,

    I am totally renovating my home i've just bought. We've ripped out al the plumbing plus had a new 25mm MPDE water main installed with good pressure.
    We're doing a loft conversion so there will be a total of 3 floors with 2 bathrooms (1 on each upper level). I am trying to design the system to minimise flow rate/pressure drops when more that one outlet is in use (2 showers for example). The main premise being trying to avoid that dreaded shower fluctuation when an appliance or tap is in use.

    So......

    I was thinking of running a 22mm cold flow throughout the house T'ing of to 15mm for the various outlets, Keeping the 15mm runs as short as possible. The boiler supply will be closest to the stop cock so this should get fed 1st and should avoid the supply rate dropping to this i assume?

    i am a bit stuck with the loft though. Should i run 22mm to the 1st floor, feed the 1st floor bathroom then continue up to the loft/2nd floor.

    or....

    is it worth running 2 separate 22mm flows, one to 1st floor bathroom, one to the 2nd?
    My thinking is that if i do this then the loft supply shouldn't be interrupted by any use by the 1st floor. E.g. every room is running direct off mains pressure without interuption. Is my thinking correct?

    I would also appreciate any thoughts on hoe to run the hot water. The issue there being it's a combi boiler, so only 1 15mm outlet to supply the whole house. So how to do i avoid drops there?

    The boiler is 35kw and has a 14.5L flow rate. i have read that a 15mm pipe can only run max 8L/pm flow, so if i have 2 showers running and the boiler offers 14.5 per min, does it mean in effect the 2 showers would still be getting 7.25L/per min???

    many thanks in advance

    Carl
     
    Last edited: 10 Nov 2015
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  3. Dan Robinson

    Dan Robinson

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    Not much you can do.

    Flow restrictors in the shower and 22mm pipe from the boiler to the split point.

    You could run a manifold on the hot and cold to give each appliance its own draw off, but frankly, it won't be worth it.

    You should have gone up a size and get an unvented cylinder.

    35kW combis are largely pointless really.


    It should be noted that you haven't given us the static and dynamic pressures.
     
  4. The boiler will have a 15mm cold feed and 15mm hot outlet. :whistle:
     
  5. Cael Mills

    Cael Mills

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    Hi Dan,

    Thanks for the reply. Sadly because of the loft conversion we were too limited on space to get a cylinder. You say about running 22mm from the boiler to the split but this surely isn't possible beacue the boiler only has 15mm DHW outlet? Also i'm afraid i don't know the static and dynamic pressure (way over my head! )

    Hi MJGas,

    I know the boiler only has 15mm DHW feel and outlet, i mentioned this in my original post. Thats' why i'm looking for the best solution, so i don't quite understand your point?

    Regards

    Carl
     
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  7. Dan Robinson

    Dan Robinson

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    The point being there is very little worth doing. Having a loft extension does not preclude having a cylinder.
     
  8. Cael Mills

    Cael Mills

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    So bottom line, for all their talk of flow rates and kw output, the reality is combi boilers just can't hack the demand on their own regardless of how high the output?
     
  9. Agile

    Agile

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    It just demonstrates the lack of professionalism in the industry for anyone to specify a boiler without knowing the mains water supply characteristics.

    It also seem that the limitations of a combi have not been discussed with you either.

    For the minute extra cost I would have fitted a 32 mm new water supply too.

    Tony
     
  10. Cael Mills

    Cael Mills

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    Hi Tony,

    Thanks for your response. Sadly the company that fitted the water main didn't even give me an option! i wish i knew 32mm was feasible.

    As your the heating engineer, i explained what we were having and he just said a 35kw combi would be fine so it would appear i've been ill advised.
     
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