boiler size

Discussion in 'Plumbing and Central Heating' started by mon, 15 Jan 2013.

  1. mon

    mon

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    hi. thinking of replacing ancient heat only boiler for a worcester green star heatslave combi oil boiler. the house heated nicely with existing size rads, i will problably replace them with same size newer ones. there is bathroom, with bath, basin, toilet, elec shower. 1 kithen sink.
    total btu`s of rads: 49458 ish.
    do you think a heatslave 12/18 will be big enough for system, will a 18/25 or a 25/32 be too big? thanks.
     
  2. Agile

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    A combi is rated for hot water output.

    24 kW is the normal minimum and this will supply about 8-9 li/min at 35 c temp rise.

    In practice this means a combi will supply just one outlet. Fine for a small flat with one or two people not very suitable for a house with more living there in my view!

    Tony
     
  3. oilboffin

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    I think you'll need the 18/25at the very least there a very good boiler there is a lot on this island
     
  4. dcawkwell

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    Small house the 12-18 will do nicely.
    Larger house the 18-25.
    Big house the 25-32
     
  5. dcawkwell

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    This is an oil boiler. Water delivery rates are nearer 20 litres a minute.
    Because they are use a heat store.
     
  6. mon

    mon

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    Thanks to you all for your advice, from what your saying it sounds like the 18/25 should be fine? 1bathroom, abt 10 rads in total.
     
  7. Agile

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    Until the stored heat is depleted after a few minutes when they revert to what the boiler output can deliver.
     
  8. dcawkwell

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    Grant specs for their combi.
    Average temperature draw off of 50 degree for 100 litres and 4 minute
    recovery time even on the smallest boiler. Impressive.

    **************
    VTXCOMBI21*
    15 litres per minute at an average temperature of 50°C
    Recovery time 4 minutes approx. Based upon 100 litre draw off.

    VTXCOMBI26*
    17 litres per minute at an average temperature of 50°C
    Recovery time 4 minutes approx. Based upon 100 litre draw off.

    VTXCOMBI36*
    20 litres per minute at an average temperature of 50°C
    Recovery time 3 minutes approx. Based upon 100 litre draw off.
    ***************
     

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