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  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?
  16. n141311

    n141311 New Member

    Plumber is an individual. Won't be able to cover cost of materials (walls were thermally upgraded before being acoustically sealed and skimmed) let alone labour for other specialist trades. He has cocked this up royally but refuses to accept it will make a difference - believes Bosch over spec'd. At this point, priority for me is to assess impact, understand way forward as I don't want the other trades men being held up. Suing him at this stage doesn't help anyone. All pipework has been halted but theres still 2 thirds of the remaining property left to pipe up and for the boiler / cylinders / pumps etc to be installed.
  17. Chalked

    Chalked Plumber GSR

    Where abouts in Yorkshire are are you?I could have a look for you if its fairly local
  18. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    your in leeds are you mate?
  19. n141311

    n141311 New Member

    Yeah I'm in York - about 30mins from Leeds.
  20. n141311

    n141311 New Member

    Hi mate, yeah I'm in York - is that local enough for you? Would be good to have someone take a look / chat with plumber who did the cock up to see if there's some way forward. I will also ring around some M&E outfits tomorrow to see if a proper design can be done. @ShaunCorbs@ShaunCorbs - do you know anyone you can recommend? I have CAD drawings.
  21. n141311

    n141311 New Member

    Hi mate, yeah I'm in York - is that local enough for you? Would be good to have someone take a look / chat with plumber who did the cock up to see if there's some way forward. I will also ring around some M&E outfits tomorrow to see if a proper design can be done. [​IMG]@ShaunCorbs - do you know anyone you can recommend? I have CAD drawings.
  22. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    You are gonna need more kw bud and upsize the main run pipework 35mm minimum, i would suggest cascading two boilers this will give you more options if needed ,installed alot of systems like yours get a proper ME consultant involved regards kop
  23. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    no sorry bit far from me and i think chalked is in leeds
  24. Chalked

    Chalked Plumber GSR

    I'm 10 mins from York ( near Tadcaster) I'm working over towards Hull this week, but could pop over early morning or late afternoon this week.
    Give me a ring on 07808914448
    • Like Like x 3
    • Agree Agree x 1
  25. scott_d

    scott_d Plumber GSR

    Lol at the pump
    It's meant for a small combi

    Did Bosch spec a booster pump, break tank etc?
  26. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Darren jackson is in leeds based another possibility ?
  27. Chalked

    Chalked Plumber GSR

    Hi mate
    Sorry I didn't ring you back. I didn't save your number, so could you ring again?.
    Pm sent too.
    • Like Like x 1
  28. Chriswareham

    Chriswareham GSR

    loveing your calculations will relook when sober
  29. n141311

    n141311 New Member

    hey guys,

    Just a quick update. So I've got an M&E engineer involved and he's come up with the same conclusions as some of the posts here. Kudos to @ShaunCorbs@ShaunCorbs -

    - M&E challenged boiler size if I'm to reheat the 2 x 300l cylinders at 25 litres per minute in tandem. Says it needs to be bigger than 50kW - probably closer to 80kW. Thoughts?

    - he also reckons that I'm going to struggle to get 11.5 litre per min pressure to the showers thanks to the plumber cocking up pipework with 15mm. His suggestion is to use a series of 3 Rennai gas-powered condensing heat generators that operate similar to boilers for endless hot water which gets around cylinder capacity / reheat. No idea if this solves the pressure problem though. I am keen to retain unvented system because a) it delivers high pressure hot water b) is super energy efficient which means low running costs c) highly reliable . the rennai website link is here: Rinnai :: Products

    - third issue he sees is that the 15mm pipework will prevent sufficient hot water temperature reaching the showers so said we might need to compensate and increase temperature to shower supply but that this might take away from radiators. I don't quite understand this but will explore when I chat with him again.

    What are you thoughts on this? My view is that if possible I'd like to retain unvented cylinder system, up-size boiler if needed but not sure if there's any equipment we can add to design to compensate for pressure loss to showers thanks to 15mm pipework
  30. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    would think if you wanted the re heat times as you stated with heating on the same time 100 kw is what you want, if your happy with a slightly longer re heat time (approx 20 mins more 80kw sounds about right)

    rinnais are very good and can handle the load but its more cost (alot more) esp if you have already bought the cylinders but agree with his pressure/flow thoughts as hes on site

    dont agree it will limit hot water temp, under sizing will only limit flow rate and esp if you havent got a secondary return it will add to the water draw off before it hot

    you have two options (one you might not like)

    one try and get as close as you can and re pipe in correct size (and hope its enough)

    two re pipe the lot and either put the costs onto the inexperienced plumber for any damage to the walls / finish

    best option is normally the worst sorry to say

    sorry i couldn't be of more assistance
    • Like Like x 1
  31. n141311

    n141311 New Member

    Hi Shaun,

    Cylinders and boilers haven't been purchased yet.

    What are the pros / cons of the Remmai solution vs unvented cylinders in your opinion? I'm concerned about the 3 things: instant hot water, delivered high pressure, in a cost efficient manner so I don't get killed by running costs

    Appreciate your experience mate.
  32. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Right ok (thought they had been )

    Both if installed correctly will give instant hot water

    Your water main governs both so no difference there

    You need a high pressure water source either mains fed or tank and booster set (I would recommend the second if you have the space)

    Usage should be about the same

    One downside to the Rinnai's is more to go wrong than an unvented cylinder

    Other than that there about the same
  33. n141311

    n141311 New Member

    Gotcha. Ok so my thinking is if I have a breakdown, I really don't want to stuck trying to find a plumber that can sort it. appreciate your other points - didn't realise it was virtually identical in all other aspects.

    Got another thought: if we upgrade where we can & pray...there is still the rest of the house yet to be piped up. If we do that properly, will those other rooms at least get high pressure water without any issues? Or are we now f* through the whole house because part of the piping is in wrong size?
  34. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    The only part that will be effected is the bits he's done / you can't get at

    If the other parts / the rest is done right / to what somone works out they should be fine

    (Hope that makes sense)
    • Like Like x 1
  35. n141311

    n141311 New Member

    Thanks mate. That message made my night. Have been crapping myself thinking the whole house might be compromised. Thankfully the guy only did 4 rooms.
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