Posting a message to the forum will remove the above advertisement
  1. Checkout our Plumbers Insurance area - heavily discounted Public Liability Insurance and Van Insurance specifically designed for plumbers.

Discuss Upgrade from 15mm to 22mm worthwhile? in the Fittings & Pipes area at

  1. Muppet7

    Muppet7 New Member

    A present I have a 25mm MDPE main pipe to stop cock. From here it reduces down to 15mm copper pipework.

    This 15mm copper pipework then splits into 2 x 15mm copper pipes, 1 pipe feeding the cold mains and 1 pipe feeding the unvented combi boiler.

    Is there any benefit in upgrading the front part of the system to 22mm? so 22mm from the stop cock to a 22x15x15 tee to the cold/combi?.

    This originally came about after looking into fitting a pressurised accumulator and needing a 22mm upgrade anyway. I'm just wondering if the 22mm upgrade would make any difference to flow rates on its own without the accumulator?

    example: shower on and someone then opens a cold tap, would there still be sufficient flow at the 22mm tee that the flow to the combi doesn't reduce?

    Hope that makes sense, I'm clearly no plumber, but i'm not lacking in enthusiasm or determination to have a go at something.
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    It's worth a try but I don't think you will gain that much more
    • Agree Agree x 1
  3. justlead1

    justlead1 Trusted Plumber GSR

    By increasing pipe size you reduce frictional resistance. However if say the proposed 22mm is only 1m in length the flow rate increase would be minimal. But if the length of 15 mm too the tee was say 10 m the flow rate when 22mm is employed would be a marked increase. As well as pipe length elbow and valves etc have an effect (more friction)
    To calculate discharge from a pipe try Box pipe sizing formula it will give you idea of how Effective length, Diameter, Head and flow rate all are combined to give an effect/answer.
    Pipe sizing is one of the most important parts of plumbing but overlooked by most.
Similar Threads - Upgrade 15mm 22mm Forum Date
System upgrade unvented etc Central Heating Forum Jun 30, 2018
Wireless controls to upgrade gravity system Gas Safe Registered Plumbers Only May 17, 2018