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15mm or 22m for correct gas pressure

Discussion in 'Plumbing and Central Heating' started by rhinosaw, 8 Feb 2019.

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  1. rhinosaw

    rhinosaw

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    had a couple of quotes for replacing an existing vented CH System S plan, going to pressurised system (not hot water ) either WB or Vaillent. 15kw. (system boiler or heat only.

    last quote said that 15mm gas feed is OK so long as there is 16.5 operating pressure, is that correct figure please? no other gas appliances in the property (flat).
    thanks
     
  2. FiremanT

    FiremanT

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    Not entirely. There must be a maximum pressure loss of 1mb between meter outlet and immediately before any appliance, when ALL are running.
     
  3. footprints

    footprints

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    Normally 22mm these days perhaps a short run of 15mm (metre or so) up the wall would be OK.
    How can he know his working pressure until the new boiler is installed? The gas rate may be different to the existing one.
    I would go for 22mm.
     
  4. Iamchamps

    Iamchamps

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    I have a 1 metre run from gas meter to boiler which was in 15mm since house was built when new boiler was fitted the instructions stated it should be 22mm. That meant destroying part of my kitchen to do that so the fitter agreed on 15mm and has been no issues.
     
  5. rhinosaw

    rhinosaw

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    Thanks for replies, I suppose that I just assumed that there has to be 16.5 coming out of the gas pipe into the boiler but looks like not so simple. I know a bit about CH systems but nothing about gas pressure, I don't really want to pay for increasing the pipe size to 22mm unless I have to. I thought that 15kw is one of the smaller boilers so not so much gas required?
     
  6. durhamplumber

    durhamplumber

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    There never would be an issue with 1 metre 15mm domestic run to a boiler
     
  7. Dan Robinson

    Dan Robinson

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    Really? :LOL:
     
  8. durhamplumber

    durhamplumber

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    I am sure you gonna find 1 Dan..The example with multi appliances and a humongous boiler...Should of said 1 appliance....Narrows it down for you!
     
  9. Dan Robinson

    Dan Robinson

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  10. John D v2.0

    John D v2.0

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    Even with 1 appliance if you have enough 22mm and elbows before, that 1m of 15mm could easily go over the edge! There's always a point where it goes over the limit.
    Edit: although i read it as 1m of the run couldn't be changed, but it could be that the whole run is 1m long with no elbows?
     
  11. durhamplumber

    durhamplumber

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    Obvioulsy, i meant 1 run.1 metre.1 appliance.
     
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  12. durhamplumber

    durhamplumber

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    Nissan luxury Coupe
     
  13. durhamplumber

    durhamplumber

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    How many elbows you going to have on a 1 metre run!!!!
     
  14. John D v2.0

    John D v2.0

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    Yes realised that afterwards, 1 metre with no elbows and bends in the mix! Although you might hear the sonic boom of gas rushing through the pipe
     
  15. Dan Robinson

    Dan Robinson

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    Domestic sized boiler.
     
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