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Discuss Ahhh is there an M&E plumbing contractor in North East that can help me in the Plumbing Forum area at

  1. n141311

    n141311 New Member

    hi all,

    I know this is a long shot but I'm wondering if there are any M&E contractors who specialise in plumbing that can help me. I think my plumber has messed up the plumbing for my property by using the wrong pipe size [​IMG]


    I've got an 8 bedroom, 8 bath property that I'm refurbishing and want to have piping hot, high pressure showers in the ensuites with a system that can accommodate all showers being used at same time during peak periods. As the property will be used as a boutique luxury hotel - these design requirements are a must.

    The property is split into three sections with the boiler being located in the centre - with 4 bedrooms on one section of the house, and another 4 bedrooms on the other section of the house.

    I had Bosch do me a system design to meet this design challenge and they proposed an unvented system comprising:
    • 2 x Greenstore cylinders 300l
    • Worcester GB162 50kw boiler
    • Salamander home boost pump
    • 28mm piping branching into 22mm
    • No point double coiling

    The inputs they were given along with layout designs were:
    • -!Current standing pressure is 4.2 bar
    • - Over 22 litres per minute flow rate on cold
    • - At 4bar pressure, shower will deliver 17 litres of water per minute
    • - 8 thermostatic showers to be installed at the property and used during peak periods
    • - 8 size heated towel rails (to come on at same time as radiators) - 1,119 BTU per radiator
    • - 15 radiators - average 3,500 BTU per radiator
    • Property is split into two sections with the boiler being located in the centre: section 1 will have 4 bathrooms section 2 will have 4 bathrooms
    • - During peak times (mornings) 8 showers will be used simultaneously!
    • - Heating will be on 8hrs a day, 7 days a week during the winter
    • - Heating will be on 3hrs a day, 7 days a week during the summer


    I had work start on section A of the building comprising 4 bedrooms and bathrooms. The plumber re-did all of the pipework for radiators, hot and cold feeds for showers and basins....except he decided to use 22mm pipework branching off into 15mm instead of follow Bosch' guidelines.

    I am now worried about the impact this deviation will have - will it still be able to meet the design challenge or does it make no difference?

    I did some back of the envelope calcs and wondered if someone can:

    a) help me validate if my back of the envelope calcs / assumptions / conclusions are correct? I am not an engineer or plumber.

    b) suggest if there's a possible fix to still ensure I can meet the design challenge for the rooms that have already been piped up (luckily they are positioned close-ish to the boiler)

    I have a CAD version of the property layout as well las technical docs for all of the proposed equipment to go in.


    Grohe Grohtherm Cube Perfect Shower Set - 34506000
    • Assuming 11.5 litres per minute flow rate per shower
    • Ave shower time will be 20mins
    • Assuming 8 showers during peak times, that’s 92 litres per minute required
    • 22mm pipe has flow rate of 0.6 litres per second // 36 litres per minute
    • 28mm pipe has flow rate of 1.1 litres per second // 66 litres per minute

    Assuming there will be a feed for section A of the property covering 4 bathrooms and another feed for section B covering bathrooms, this means max flow rate required will be 11.5 litres per minute * 4 showers = 46litres per minute needed from each main feed

    Conclusion 1. 28mm piping should be used to meet the 46 litres per minute (22mm would be restrictive at max flow of 36)

    However, there is also the issue of ensuring the cylinders themselves can supply enough water given peak time demand and then push it through at appropriate flow rate to avoid loss of pressure. To aid this, the spec indicated 2 x greenstore unvented cylinders at 300l each.
    • Greenstore SC300 can re-heat 300l of water in 24 mins = 12.5 litres a minute
    • At 2 cylinders in tandem, this means a re-heat capacity of 25 litres per minute
    • Going back to design challenge of 8 showers on at same time during peak periods:
    • 600 litre total capacity would be used up in 6.5mins (600 litres / 92 litres per min)
    • But in those 6.5 mins, the cylinders would reheat 163 litres of water (25 litres per min reheat capacity * 6.5 mins) = 1.7 mins
    • Total shower time at max demand: 8.2 minutes (6.5 mins from 600 litre capacity + 1.7 mins from reheat capacity)

    Conclusion 2. while this doesn't quite meet the 20 mins at 100% utilisation, I think Bosch' proposed 2 cylinders is quite balanced because not everyone will shower for 20mins and it's unlikely that all 8 showers will be used at exactly the same time for exactly the same duration. If one or two people did find cold showers, total reheat time is quite healthy at 25l per minute - essentially covering 2 showers at 11.5 litres per minute flow rate.


    I know I've totally neglected pipe runs and the number of bends. I have layout drawings and a CAD version of layout that I can share if necessary.[/LIST]
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    I think your going to have fun at the start

    Got a few questions

    What boost pump have you got / link or pics and do you have a tank supplying thins or just straight off the mains

    And what's your incoming mains pipe size ?

    To get a re heat time for your cylinder (24mins)

    You need to have 39kw going through the coil

    And you have two

    So there's 78kw just for the cylinders and let's say another 20 for rads etc

    So that's in the middle of winter you need 98kw heating load for a re heat time of 24 mins

    Let's say your fine with 48 mins re heat time

    You need aprox 19.5 kw per coil (39kw for both coils)

    Plus your 20 for your heating 59kw needed

    Where in the country roughly are you ?
  3. n141311

    n141311 New Member

    Hi Shaun,

    I'm based in Yorkshire. We have a U16 gas meter providing mains supply to the boiler. The re-heat time came from the Greenstore TC300 spec.

    Salamander home boost pump (not yet fitted): Home Boost

    Greenstore TC300 cylinder: Greenstore SC Cylinder Series - Worcester Bosch

    In terms of the pipe sizing to achieve design requirement - do you have a view on this? Part of house has been done in 22mm branching into 15mm but Bosch had specified 28mm branching off into 22mm.
    Last edited: May 7, 2017
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    • Like Like x 1
  5. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Right your on a looser before you start

    That pump won't do anything for your mains water

    You would need either a break tank and pump to push your lpm up to around 80-100lpm

    Or an accumulator sized correctly

    42-35mm to the cylinders in and around 35-28mm out and to close as possible to each set of 4 then 22mm to each

    Also pg 7 on your manual indirect coil heat exchanger rating in kw
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    My best advice is start looking for a commercial heating engy

    Because you will need other things like

    secondary returns
    Low loss header
    Balancing valves depending on length of circuits

    • Agree Agree x 1
  7. Chuck

    Chuck Active Member

    I think you should seek advice from a company, or consultant, who does a lot of this type of work. It definitely looks 'commercial' not 'domestic' to me and needs to be 'designed' not lashed up using rules of thumb.

    The assumptions you put in about what performance is needed at periods of maximum demand are going to make a big difference to the cost and performance of the system. E.g. where did you get the '20 mins' average figure from? The average (domestic) shower apparently lasts 8 minutes:

    People's showering habits revealed in survey - BBC News

    and that average includes teenagers!

    I imagine that, if one knows where to look, there are data available for shower usage patterns in hotels.
  8. tolly

    tolly Plumber GSR

    Sounds like you need a Mechanical Consultant first unless you can find someone you trust to D&B.

    Crazy if Bosch specced a Salamander home boost pump!
    • Agree Agree x 1
  9. n141311

    n141311 New Member

    Hey all,

    Thanks for so much for the replies. Bosch didn't spec the salamander pump...that was the plumber who cocked up the pipework. Sigh.

    Can anyone recommend a good mechanical consultant and plumber in the Yorkshire area that can help? The problem is that a lot of the M&E firms seem too big to care about a job this size, but it's too large for the smaller plumbing firms.

    None of this would have been needed if the plumber had just followed Bosch' spec.
  10. n141311

    n141311 New Member

    Hi Shaun - thanks mate. Even with secondary returns, etc - can the situation be rectified given part of the plumbing has been done in 22mm branching into 15mm? I don't want to rip it out as 4 of the rooms have been acoustically over-boarded and skimmed
  11. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    How close could you get to the 22mm and what's he done t off the 22mm to each appliance with 15mm ??
  12. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Did you ask him why he's done it his way and not the specd way ?
  13. n141311

    n141311 New Member

    Yeah he said he did it in 22mm to 15mm because his "experienced mate" told him Bosch had way over spec'd it and he'd always seen piping done in 22mm into 15mm. He also said that 'no point doing it in 28mm to 22mm when the inlet valves for all the showers are 15mm'
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    TBH I would get rid of him based on his replys

    And it all depends on distance more length bigger pipe required
    • Like Like x 1
    • Agree Agree x 1
  15. Chuck

    Chuck Active Member

    Try here, see if anyone bites:

    Find a Plumber, Tiler or Electrician

    I'm puzzled by why work that clearly doesn't meet a written spec is a problem for you and not the plumber who installed it wrongly. Have they gone bust?
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