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Boiler choice

Discussion in 'Plumbing and Central Heating' started by londoner1, 23 Mar 2015.

  1. londoner1

    londoner1

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  3. AngelesPlumbing

    AngelesPlumbing

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  4. Phill Peck

    Phill Peck

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    Almost all manufacturers make a storage combi

    Vaillant 937
    Viessmann 111/222
    Glowworm ultra store
    Worcester highflow
    Etc etc

    You still need a good incoming main even with a storage combi though.

    I've got a standard combi (Vaillant 831) at home at it can cope with 2 taps there is a slight difference in the shower if another tap is used but still reasonable. My water main delivers 25ltrs/min though
     
  5. Hessles

    Hessles

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    As above, check your main incoming flow rate and dynamic pressure. Easy to do with a bucket and pressure guage.

    I'm in the process of having a Viessmann 222f installed, looks like a really good piece of kit that'll deliver 20 lpm of 60 degree water as it stores 130 litres in the bottom, once depleted it falls back to the combi rate. It's heated by a plate heat exchanger instead of a coil so the reheat time is reduced!

    Fits in the place of a 600 wide cabinet so can be "integrated" into a kitchen or utility.
     
  6. Agile

    Agile

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    The makers of storage combis don't usually point out that once the store is depleted the flow rate become average.

    So many installers don't seem to understand either. When the Vaillant 937 came out I asked those installers how long before they reverted to the basic flow rate. None seemed to be aware.

    Even a 24 kW combi will supply three taps! But only at 3 li/min each. Without giving the technical details such statements are of no use.

    The Viessmann are particularly good because the store is quite large.

    Saying your mains flow rate is 25 li/min is useless when that's only the open pipe flow rate.

    Its the dynamic flow rate that matters!

    Tony
     
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  8. BigSnoopy01

    BigSnoopy01

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    one thing to consider is flow restrictors at the taps if you need to share the flow rate from a combi. If you have a good water supply then any combi is a poor choice for multi bathroom properties
     
  9. Tipper

    Tipper

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    I don't think you are right there. The flow rate will always be the same...what goes in must come out!

    What you mean is the claimed hot water supply rate will drop but not so you'd notice particularly if there is a thermostatic bath mixer or thermostatic shower involved. The initial availability of hot water in reserve will be used first and then the boiler supplies HW at it's rated output. One benefit is HW is immediately available so no waiting for the boiler to light up. This assumes the 'back-pack' is in service and fully hot of course.

    I've got 5 Vaillant Ecotec Plus combi boilers in various properties, 2 x 937, 1 x 831, 2 x 824.

    The 937s are excellent but a bit bulky on the wall. Not a good idea in a kitchen. I have one in a garage and one in a utility/boot room so not a problem. The 831 copes well with two showers but as said will dip a bit if another 'tap' is opened. The 824s just work well, they're in small flats.
     
  10. Tipper

    Tipper

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    Size or flow capacity of showerheads is important too. Many don't take account of this.
    (I have argued with my wife at length about not having a dustbin-lid showerheads! They're not suited to either combi boilers or water economy.)
     
  11. Hessles

    Hessles

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    The flow rate will change, the storage combi will use the stored water to give you a higher flow rate of hot water than it can deliver on its own!

    My 222f will give 20l/s until the store is depleted and then it'll fall back to the standard rate
     
  12. Hessles

    Hessles

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    Quite a lot of the modern shower heads I've been looking at are restricted to 9.5lpm
     
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