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High end Combi vs. Unvented for 3-bed semi-D & 1 bath.

Discussion in 'Plumbing and Central Heating' started by EMFTeo, 18 Jan 2012.

  1. picasso

    picasso

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    The unvented cylinder and system boiler would be a better choice if you have the budget and space, although I like combi boilers I have an unvented cylinder in my own house, if you can stretch your budget you wont be sorry you went for the system/unvented .
     
  2. EMFTeo

    EMFTeo

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    How much did you invest in it?
     
  3. picasso

    picasso

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    The boiler was about £600 and the cylinder roughly the same, I am a heating hengineer so the installation didint cost anything (just my weekends), beats my last house which had a combi hands down, the extra £££ is because its a better system.
     
  4. EMFTeo

    EMFTeo

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    That's all right for some.. we were quoted this for an unvented solution:

    · Strip obsolete plumbing to tip
    · Flush to heating system
    · Supply fit Vaillant EcoTecPlus 618 LPG system boiler
    · Supply fit Vaillant Unistor 155 indirect unvented hot water cylinder
    · Supply fit all controls, remote programmable room stat, motorised valves
    · Supply fit 22mm Magna clean filtration unit
    · Provide waste pipe work for condense
    · Commission system and notify Gas Safe Register

    £5160.00 inclusive of VAT
     
  5. linkyplumb

    linkyplumb

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    I am moving to Berkshire:cool:

    Without getting into specifics, that would be at least 2 grand less down here!
     
  6. picasso

    picasso

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    What was the quote for the 837 ?
     
  7. EMFTeo

    EMFTeo

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    £2832...
     
  8. dangas123

    dangas123

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    I would recommend you go with the combi. A viessmann vitodens 30kw to be precise. The unvented system is far better to give you your shower as they give mains pressured hot water but is more expensive and more space consuming and unnecessary for a 1 bathroom house. Being a 3 bed house im guessing you need the storage space.

    Also you dont want a power shower, you want a thermostatic mixer
     
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  10. EMFTeo

    EMFTeo

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    Is it efficient with the LPG fuel consumption..? We have 3 needs:

    1) More storage space
    2) Lower fuel consumption
    3) Good pressure for shower
     
  11. picasso

    picasso

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    yes the combi is looking like a winner.
     
  12. EMFTeo

    EMFTeo

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  13. D_Hailsham

    D_Hailsham

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    Any boiler which has been converted from NG to LPG can be converted back again. In some cases it's just a case of adjusting the burner!

    I don't know what he is talking about; and I suspect he doesn't know either. The minimum output of the 837 is 12kW and this cannot be reduced. You require 12.65kW when it is freezing outsize, so this is the maximum you require. (OK, say 15kW to allow for Arctic conditions). The 837 would be working below the modulation minimum, which can only be achieved by turning the boiler on and off.

    To add another name to the list, have a look at Remeha Combis. All models have a minimum CH output of 6kW and the maximum can be easily adjusted to meet your requirement. The HW output ranges from 24 to 39kW, so you can select the correct boiler for your HW requirement and know that it will be OK for CH as well. They come with a 5 year parts, 2 year labour guarantee.

    All models, except the 39C which requires a conversion kit, can be changed from NG to LG (or vice versa) by the installer when commissioning the boiler.
     
  14. EMFTeo

    EMFTeo

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    Its' all becoming quite confusing...

    All we want is a modern efficient boiler which can:

    1) Save LPG consumption costs
    2) Free up space so the airing cupboard can be made into a shower
    3) Ensure that the hot water is not interrupted when showering and when someone else is doing the dishes/washing machine is running.

    Fix budget of up to £3,600 maximum.

    And a competent, honest LPG Gas safe certified engineer willing to do a good job!
     
  15. muggles

    muggles

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    OK, so you've chosen the Combi option it seems. For the reasons given relating to having to work at below its maximum power output, the 837 is not suitable for your heating system. It will cycle on and off constantly, using more gas and potentially reducing its lifespan. The 831 is better, but still has a relatively high minimum power compared to other manufacturers.

    All boilers that can be converted from Natural Gas to LPG can also be converted from LPG to Natural Gas.

    At the risk of starting up the 'which combi is best' debate again, have a serious look at the Intergas Combi Compact HRE 36/30. LPG-convertible, it will go down to 7.6kw for central heating (better than the 831's 8.7kw) but also has a more powerful top end for hot water at 32.7kw against the 831's 31kw. This means you get a slightly better flow rate. The heat exchanger has a 10-year warranty, the boiler has three years (or five if installed by a Platinum 5 installer). There are far fewer parts in an Intergas than any other boiler, so there's much less to go wrong. They're also very easy to work on, making servicing cheaper.
     
  16. D_Hailsham

    D_Hailsham

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    All A rated boilers will do this; and as only A rated are permitted (with very few exceptions) this can be ignored when selecting the boiler.

    Then you need either a combi boiler or an unvented HW cylinder installed in the loft.

    That's the hardest one to achieve. It all depends on the water pressure and flow rate.

    You said you had 25lpm @5 bar from an open tap. You need to measure the flow rate at the kitchen cold tap (a) with the outside tap off and (b)with the outside tap fully on. If it's lower when the outside tap is fully on, then you should use this figure when deciding how many kW you need for hot water heating (work on 2.5kW per litre per minute).

    You can measure the flow rate with a marked bucket and a clock/watch with second hands.

    The flow rate is important for both combi and unvented cylinders as both supply hot water direct from the mains.
     
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