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Discuss New bathroom pipe size conundrum in the Bathrooms, Showers and Wetrooms area at

  1. JamesT

    JamesT New Member

    Good morning all,

    I know this is a common thread topic and the answer has probably already been provided however just wanted clarity and piece of mind.

    I have just bought a house and want to convert the bedroom above the kitchen and the boiler into an upstairs bathroom. I have already determined the pipe runs from the boiler approximate longest length 8m.

    I am installing the pipework myself but want to know whether I should run the main DHW from the boiler in 22mm as the main "header" and then branch off for the shower and sink in 15mm? Or should just run it all in 15mm (already bought all 15mm pipe and fittings in 15mm). Would I notice the difference if I run it in 15 or 22?

    The boiler is quite an old Worcester 9.24 boiler with 15mm DHW outlet and 15mm Cold water inlet, the flow out of the hit water is approx. 9.5litres/min

    There are 9 radiators in the house.

    I hope I have made it clear what is going on and what I require clarity on.

  2. scott_d

    scott_d Plumber GSR

    15mm is plenty if you only have 9lpm
  3. JamesT

    JamesT New Member

    I thought as much however I then thought if in the future maybe a year or so I decide to upgrade the boiler would it not be wise to install 22 in preparation for it or will most combi boilers be ok on 15?
  4. scott_d

    scott_d Plumber GSR

    Most combis are 15mm outlet on the hot so not really worth it.
    What Lpm do you get from the cold?
  5. JamesT

    JamesT New Member

    Cold water lpm is around 17
  6. snowhead

    snowhead Well-Known Member

    Using 22mm will create a larger volume of cold water to be cleared before Hot comes through.
    This will mean excess use of water and gas.
  7. scott_d

    scott_d Plumber GSR

    15mm is fine for the hot and cold to a bathroom
    If you are doing other work you could upgrade the cold supply for future.
    22mm from the stop tap with a 15mm branch for the boiler, 15mm branch to kitchen, 15mm to branch bathroom
  8. JamesT

    JamesT New Member

    Ok thanks snowhead, I'll run it all in 15mm...what determines the pressure of the hot water then?
  9. JamesT

    JamesT New Member

    Ok what benefits would that give me just a greater flow rate and pressure around the system?
  10. Riley

    Riley Plumber GSR Top Contributor!!

    Remember a new bathroom site is notifiable
  11. JamesT

    JamesT New Member

    Who do I notify and how much does it cost me? Why do I have to notify people?
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Building control

    Also they might want to come out and inspect the first fix wastes etc
  13. rpm

    rpm Trusted Plumber

    PS He is in Cardiff Shaun, any difference there?
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    No only difference would be in Scotland
  15. JamesT

    JamesT New Member

    Thanks Shaun, I'll look into it and see what I need to do
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