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Combi vs unvented

Discussion in 'Plumbing and Central Heating' started by FRAN1870, 5 Feb 2019.

  1. FRAN1870

    FRAN1870

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    Had two plumbers round and both have given conflicting advice.

    Basically I’m having a new water main put in to seperate an old lead shared supply with a low flow rate.

    Ideally I want two showers to run at the same time because I’m only getting 10l per min at 3.5bar

    First plumber says ... fit an unvented cylinder and the hot / cold balancing valve will give you mains pressure. Didn’t say anything about upgrading existing pipes!

    Second plumber says ... unvented cylinders are more trouble than they are worth and I should have a bigger combi to replace my 5 year old Bosch CDi 30. This is because it’s impossible to run two showers simultaneously and I would need to upgrade the whole house to 22mm with an invented!

    Thoughts?
     
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  3. Dan Robinson

    Dan Robinson

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    Please clarify this statement..
     
  4. Dan Robinson

    Dan Robinson

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    A stupid statement

    Not a totally stupid statement

    You won't get two decent showers from a combi no matter what size water main you have.
     
  5. FRAN1870

    FRAN1870

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    At the moment I have two electric showers .. they can’t run at the same time because of the low flow rate. (Ignore the electrical amps issue at the moment, it’s not my intention to try and run them at the same time electrically).

    I want to end up having two thermostatic mixers but this move lays the foundations.

    My girls are only primary school age so don’t fight over the shower just yet.
     
  6. FRAN1870

    FRAN1870

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    That’s what I thought hence the lean towards unvented... or there may be a possibility to run one leccy and one mixer?
     
  7. Dan Robinson

    Dan Robinson

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    At 3.5 bar, a new 32mm main will be able to run an unvented cylinder perfectly well. You'll need 22mm cold supply to the cylinder then 22mm to the split point between showers. From there 15mm will probably be fine to the points of use.

    Assuming a balanced feed is taken from the safety group to the bathrooms.
     
  8. FRAN1870

    FRAN1870

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    I think they’ve quote 25mm mains pipe... it’s 40lpm at the road
     
  9. Dan Robinson

    Dan Robinson

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    I'd be asking for 32mm, but 25mm is still a vast improvement.
     
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  11. Razor900

    Razor900

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    Go unvented and keep the CDi. No need to scrap a perfectly good boiler
     
  12. ScottishGasMan

    ScottishGasMan

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    Personally I would go with the Unvented. Even if you had a high flow rate combi, the unvented would be able to supply the water at a higher temperature, therefore better showers when mixed with the cold water. Plus the option to have an electrical immersion heater if the boiler breaks down will be invaluble when the kids are older and have even less patience than now.

    if you live in a house where you could only have say 15 litres a minute max flow, then a big combi would be fine, if hot water is important and you have the potential to get the higher flow, then go for an Unvented every time.
     
  13. Dan Robinson

    Dan Robinson

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    Don't forget about immersion heater backup.
     
  14. FRAN1870

    FRAN1870

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    Immersion heater ... like the good old days


    Thanks fellas, I think the unvented is the way to go..... now I just need to find someone to fit one!
     
  15. Dan Robinson

    Dan Robinson

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    Ask neighbours and friends first. If you contact The Intergas Shop, they sell Joule cylinders and may know someone near you that is open minded.

    Remember this is a major capital investment in your property and price should be secondary to quality even if it means waiting a while. Anyone that can do this level of work at a drop of a hat should have good reason to be available.
     
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  16. FRAN1870

    FRAN1870

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    Thank you and yes I agree ... with unvented what am I signing up for maintenance wise?
     
  17. Dan Robinson

    Dan Robinson

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    Nothing major if you have a good boiler man.
     
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