New boiler installation

Discussion in 'Plumbers' Talk' started by SylviaCB, Jan 17, 2020.

  1. SylviaCB

    SylviaCB New Member

    Hello, we have 4 bedrooms house 2 bathrooms, our plumber said we need system boiler and he proposed Vaillant EcoTec 637, 37kW. Currently we have 15mm gas pipe from the meter but he said the current gas regulations require 22m pipe. Is he correct? We have the pipe installed under the floor and it is going to be a lot of work to replace that. Maybe we could actually get 30kW model and this will go ok with 15mm?What are the current gas regulation for pipe size for system boilers thank you
     
  2. Mike83

    Mike83 Well-Known Member

    It’s not a regulation that states what pipe serves what boiler.
    It’s a calculation that has a few variables.
    But 15mm is usually insufficient. With a 37kw boiler it’s a definite no.
     
  3. SylviaCB

    SylviaCB New Member

    Would 15mm be ok with 30kW, and 30kW would be sufficient for 4 bedroom house/2 bathrooms?
     
  4. dcox

    dcox Active Member

    As above. I’d always factor in upgrading the supply when quoting for a replacement boiler if the current supply is 15mm. Modern boilers draw a lot of gas when they start but then modulate down when they’ve warmed up.
     
  5. SylviaCB

    SylviaCB New Member

    Our plumber just said this is required by gas safety regulations that system boilers need 22mm, nothing about efficiency or what is best for the boiler ...
    Is there any gas regulation in regards to system boilers? I know that all combi boilers require 22mm pipes
     
  6. dcox

    dcox Active Member

    There is a test to check that the boiler is getting enough gas when it’s working hardest. If the pipe is undersized it will fail the test. It must pass the test to comply with gas regs.
     
  7. Mike83

    Mike83 Well-Known Member

    A 30kw system boiler may be a bit much.
    It depends on the full system requirements.
    How many radiators and cylinder size needs considered.
     
  8. SylviaCB

    SylviaCB New Member

    14 radiators and 200l cylinder, 130m2 house
    He said we need Vaillant EcoTec 637 which is 37kW
     
  9. Heat

    Heat Well-Known Member

    A system boiler is just the same as a combi boiler except the combi has hot water heating.
    So I am not sure why system boilers could be mentioned in regards to gas pipe size.
    The gas pipe size is determined by the kilowatt maximum demand the pipe will supply, plus the length of pipe run to include extra length each bend will cause to resistance in the pipe.
    A pipe can be oversized to be certain it is ample for boiler and to serve potential extra demand or extra gas appliances in the future.
    Check with another gas installer who will confirm your installer is correct
     
    SylviaCB likes this.
  10. Mike83

    Mike83 Well-Known Member

    If he did want to fit a 37kw boiler I would probably go with 28mm either partial or full run.
    Your 14 radiators may require 10-15kw. If it’s a more modern house then even less.
    This would leave the rest to supply the cylinder which is overkill.
    You don’t want to grossly oversize the boiler as it won’t modulate low enough when there’s less or low demand.
    I have 14 radiators and a 200 litre cylinder. New build house. 15kw boiler.
    My heating and HW times are staggered through the day. I notice zero drop in performance. Radiators always heat up within minutes.
    I’m not for one minute suggesting a 15kw boiler but 37kw for me is a big no.
     
  11. SylviaCB

    SylviaCB New Member

    I just told him this I he doesn’t agree with 15kW for us, I think I will get some other plumber locally to confront him, don’t want to invest £1500 in boiler which we actually dont need. Thank you
     
  12. Mike83

    Mike83 Well-Known Member

    Regardless of what kw boiler you fit a pipe upgrade may be required.
    Lots of boilers will work with undersized pipes but it’s the pressure loss from the meter to the appliance that matters.
     
  13. SylviaCB

    SylviaCB New Member

    Thank you for your reply Mike.
    Is the oversized boiler a problem?
     
  14. Mike83

    Mike83 Well-Known Member

    If the boiler is oversized for the gas pipe then it could lead to incomplete combustion of the gas.
    If the pressure at the appliance gets really low the boiler will just keep going to ignition lockout (faulty).
    The thing is that us as gas men need to do the job correctly. We need to ensure the boiler is safe and fitted correctly. This usually involves upgrading the gas but not always.
    Get another quote or 2. See what others say.
     
  15. SylviaCB

    SylviaCB New Member

    Thank you. He is saying we need higher kW because our mega flow is installed in the attic, 2 floors above the boiler so we need better pump, does this make sense? Is this any factor to be considered for getting higher kW?
    our old boiler was Ideal FF 60 which had 22kW and he is saying that it broke because the pump couldn’t pump the water to the mega flow, it was 20y old boiler same age as our house. I just want to make sure we don’t install something we don’t actually need. Thanks
     

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