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Thermal Store/Heat Bank or Two Combi's?

Discussion in 'Plumbing and Central Heating' started by JohnH74, 2 Mar 2009.

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  1. JohnH74

    JohnH74

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    Location:
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    United Kingdom
    I currently am running Two Ideal Isar Condensing Combi boilers (5 years old)

    One is completely broken, the other is on the way out.
    They run independantly for C/H on 2 zones but are T'd together for DHW (due to mains water pressure (6bar) and output requirement).

    I need to fix/upgrade my system but have received lots of different advise.

    Requirements:
    Around 32kw c/h total output to feed approx 20 radiators.
    DHW requirement, not sure but would need to run at least two high pressure mains fed shows + sinks at same time (5 bed's, 4 kids + wife in the jacuzzi bath!)

    Boilers are currently situated on 2nd floor (of 3 floors) and don't have F&E tank at top of house (don't particularly want to fit one either!)

    Would like (not essential) option of solar power in future.

    Purchase/Installation cost, Reliability, Performance and Running Costs are all factors to consider.

    Option 1:
    Replace 2 combi's with large Baxi (40kw) - not sure if will cope with DHW requirements though.

    Option 2:
    Unvented System - don't like thought of space this would take up and extra installation,servicing cost, also think thermal store as more advanced option.

    Option 3:
    Replace 2 Ideal Combi's with 2 Baxi Combi's under the current set-up.
    This would have more than enough output but would also require two service contracts etc.

    Option 4:
    Thermal Store or heat bank- not many installers know too much about them.
    Are these suitable for my requirements?
    We live in hard water area and have heard of limescale issues.
    Will they need an F&E tank at top of house?
    How do you go about getting one?

    Any advise would be appreciated.

    Thanks

    JH
     
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  3. doitall

    doitall

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    Option 2 would be my Only choice. :rolleyes:

    A gledhill sludge bucket in a hard water area, que Dr Drivel.
     
  4. swbjackson

    swbjackson

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    I'd say option 2 or go for a Rinnai twinflow set up.
     
  5. DP

    DP

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    Did a job some time ago. It comprised two combination boilers (Baxi 105e) and 300l Megaflow.

    The building was split in two- main house and granny flat. One Baxi supplied DHW to main house kitchen and utility room as well as heated the rads there. Second boiler supplied granny with DHW and heat her rads. This boiler also heated the water in the Megaflow.

    Another job was one Vaillant 635 to supply two heating zones and heat a 300l Megaflow. Megaflow fitted will allow future connection to solar panels.

    Fail to see the quibble about annual inspection or BC documentation. I see it as a safety thing that ensures no corner cutting which seems to be prevalent now. It is rare to find an installation that is someone's pride and joy instead it is 'take the money and run'

    20 rads mean nothing other than it is a large number. What is relevant is the heat output. If each rad puts out one Kwatt, 20 would need boiler supplying 20kwatt (well within the power output of a the smallest combi)
     
  6. Paul Barker

    Paul Barker

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    It's a no brainer cheapest option all things considered is a guaranteed fix service contract with ideal on the existing boilers. Make them pay for their mistakes. It is your cheaoest option all others cost 10 times as much.

    Other way to this route is have both combis in working order and sign up with British Gas we love working on ideals. We have so many to keep going your two won't make any difference. And a great response time.
     
  7. BigBurner

    BigBurner

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    Avoid unvented cylinders. First, what is wrong with getting the combis fixed? At 5 years old they are pretty newish. What was the DHW performance with the two combis? You have zoning so must be cheap to run.

    You have two choices.

    1. Install a thermal store/heat bank

    2. Replace the two combis, or just one of them. Look a Broag combi.
     
  8. JohnH74

    JohnH74

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    Thanks for the advise.

    The current Ideal boilers have had PCB replacements already, most valves replaced but the heat exchangers are knackered.
    One has been canibalised by a plumber to get the other one working.
    They have been leaking over a few years as the service contract I had on them with BG wouldnt cover 2 boilers (only 1 per household contract).

    The current boilers claimed to be 29.3kw DHW each pushing out 13.86 v/min (specification D?) each. They coped fine with one main performance shower but we have since added another performance shower/jacuzzi bath! Combined, as long as they didnt fight against each other, (which some people suggest they would), they should create around 27 l/min. This is comparable to a heat bank but it will take a combined 60kw to produce this (30kw*2).

    Considering the size of the system in a very old uninsulated house, my bills have been reasonable (but we do only have c/h set at around 18C!)

    Thanks for input.
    JH
     
  9. gas4you

    gas4you

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    Find the space needed and fit an ATAG Q solar with the 38 boiler.

    It is the most up to date, quality and reliable set up you can get and will enable solar panels to be fitted when you wish.
     
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  11. DP

    DP

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    All I can say is, 'A little knowledge is a dangerous thing'. Information gleaned from books and pamphlets should only be used as a guide not as gospel. Hands on experience cannot be beaten.
     
  12. gas4you

    gas4you

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    Good post Danny.
     
  13. BigBurner

    BigBurner

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    Nice to know the combis delivered the DHW. Pity about the poor quality. Well you can still just replace each combi with quality models. I always put the combis on separate showers and only combine for baths. Always works well.

    A vented heat bank and boiler is a great option. Have the heating system off it. Have the CH circuit using a Smart pump, TRVs all around and no central wall stat.
     
  14. BigBurner

    BigBurner

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    Spot on nearly. Intelligent engineering analysis is the key.
     
  15. gas4you

    gas4you

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    He was refering to you, you forum laughing stock :rolleyes: :LOL: :LOL: :LOL:
     
  16. DP

    DP

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    BB, can you say how you combine DHW from two combis to run a bath?
     
  17. JohnH74

    JohnH74

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    I do not proclaim to be an expert (in fact I am a rank amatuer at best), but our current 2 combi's are joined together to provide all the DHW for the entire house.

    They are T'd together just underneath the boilers and whenever a tap/shower/bath is turned on, both boilers fire up.

    The plumber who fitted them did it this way as 1 boiler on its own (14l/min) couldnt cope with the water requirement from the taps.

    I guess to run the showers on dedicated boilers and the taps on combined boilers would require separate dedicated plumbing to each shower and the rest of the DHW on a regular circuit. If this is the case, it sounds messy.

    I am currently looking at a Torrent RE 277 Thermal Store (solar capability for future), with a 30-40kw standard boiler.
    The Torrent would provide 25 l/min DHW.
    The top part of the house would be on a sealed primary system (as no F&E tank above it) feeding direct of the boiler.
    Downstairs on the house would run through the thermal store (F&E would sit on top of thermal store).
    Until I get solar (when grants are available!), I will connect the boiler to the regular heating coil on the thermal store (this is half way up) and also to the solar coil (which is only 8kw and at the bottom).
    Total c/h output required would be 30kw.
    Water output required 25l/min+ for 2 en-suites+bath+jet shower/jacuzzi.

    I am not interested in unvented system.
    It is either the above or a couple of Baxi's again.

    Thoughts?

    JH
     
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