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Discuss Joining two cold water tanks together in loft. in the Bathrooms, Showers and Wetrooms area at

  1. Wrighty8

    Wrighty8 New Member

    Afternoon guys.

    I am looking to connect two tanks together in order to supply my shower I am installing.

    I am aware that one big tank would be the best way to go however I have been given a 25 gallon tank so I want to attach the two together.\

    Here is a rough sketch, would that be ok? any issues there or a better way?

    Tanks have to be like this as there is no room end to end I f that makes any difference.


    Thoughts please?

    • Useful Useful x 1
  2. Whn1

    Whn1 Plumber GSR

    Looks good to me mate, definitely add some clips to the pipework though
    • Like Like x 1
  3. jtsplumbing

    jtsplumbing Plumber GSR

    I would be more inclined to link them together with 28mm with a 28mm leaver valve in-between
    • Like Like x 3
  4. Chalked

    Chalked Plumber GSR

    I would be fitting the ball valve in the left tank. Then taking a feed between the two. Then any outlets from the tank with no ball valve.
    This will make sure you don’t have ant stagnant water sitting in one tank.
    • Agree Agree x 4
  5. Wrighty8

    Wrighty8 New Member

    Thanks jtsplumbing, only reason I mentiond 22mm is I already have that in stock!
    Yeah I was thinking about the stagnant water angle, my theory was because the main fed cold ie taps etc are in the main tank and only the Shower is in the second tank that this would be ok.

    Doing it your way would it make a massive difference? it would mean re routing the cold mains and swapped the ballcock over like you say.
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Looks fine you want the links as short as possible

    If your using 22mm you need to link it either on the side or front and back but you will require 2 links
    • Like Like x 3

    CHRISX Active Member

    Hello Wrighty8,

    To ENSURE that You will not get problems with water stagnation you should definitely fit a Floatvalve in each CWS Tank.

    For the very small additional cost of the Valve, Pipe & Fittings and very little additional work it will ensure that both Tanks are being filled with oxygenated water at every draw-off.

    I have found quite a few problems with CWS Tanks that have been linked together where the water in the Tank that does not have a Floatvalve has stagnated.

    If You think of there being stratification levels in the `secondary` Tank - basically when the Water levels are equalising from the bottom links the upper level of the water in the Tank without a Float valve does not get used or mixed with the water flowing in from the other Tank.

    However when that Water `strata` stagnates it will contaminate the rest of the water in that Tank.

    I realise that there would usually be Oxygen in the water flowing in from the `Main` Tank which might rise up into the upper level of water in the `Secondary` Tank - depending on how much water had recently been drawn off - but that might not be enough to also re-oxygenate the upper level water - however even the water flowing in from the Main Tank may have `lost` some of its Oxygen into the atmosphere if there had not been any draw-off for some hours.

    For the very small amount of extra work and materials cost You will be able to `Guarantee` that the water both CWS Tanks will NOT stagnate.

    Because of what I have described I really don`t know why any Plumber would ever install an 2 Tank configuration without a Float Valve in each Tank.


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    Last edited: Mar 5, 2018
  8. Best

    Best Trusted Plumber

    I agree, - definitely a ball valve on each tank keeps the water moving and not stagnating.
    I have used the cold water draw off on one tank and the draw off for cylinder on the second tank. This keeps both tanks water moving and guarantees even distribution, but one concern I have is the risk of the cold draw off running dry before the hot draw off and risk of sudden hot water coming out of a shower, as pump manufacturers MIs try to avoid
    • Like Like x 2
  9. Wrighty8

    Wrighty8 New Member

    Superb stuff by everyone yet again and Chris that is very in depth thinking there and I like it :)

    I take it you meant to say never here as you say to install two ball valve's

    Thanks all, I think I've enough now to be able to complete the job in the correct way :)
  10. CHRISX

    CHRISX Active Member

    Hello again Wrighty,

    Sorry for the mistake in the paragraph that you quoted - this is what I should have written:

    Because of what I have described I really don`t know why any Plumber would ever install an 2 Tank configuration without a Float Valve in each Tank.

    I hope that You will see this message.

    I advise that You fit a Floatvalve in each CWS Tank.


    • Like Like x 2
  11. Wrighty8

    Wrighty8 New Member

    Got you, cheers Chris.
  12. CHRISX

    CHRISX Active Member

    Hello Best,

    The comments in this message are not directed at You as you will already know the details - they are for possible future readers of this thread.

    You made a very good point about the Cold Feed to a Cylinder - which should apply to EVERY CWS Tank installation - including Member Wrighty8`s CWS Tank:

    As I am sure that You have done - it MUST be connected to the CWS Tank higher from the bottom of the Tank than the Cold Water Service so that in the event of the Tank being drained while someone is having a Shower the Hot Water supply is stopped before the Cold supply.

    That would prevent the person in the Shower from being scalded by the Hot Water - even a moment of Hot Water only can cause very serious scalding.

    Especially when Shower Pumps are installed it is possible for a short burst of Hot Water only to flow from the Shower head even if the connections to the CWS Tank are level with each other.

    All it needs for that to occur is that the Cold Water supply pipework is shorter than the Hot Water supply so that the Pump `empties` the Cold supply first in the event that the CWS Tank has been drained for some reason during the Shower use.

    It is definitely possible that this can be the case because the Hot Water supply is coming from a Cylinder / Cylinder cupboard whereas the Cold supply may be taking a shorter route to the Shower from the Tank.

    When the Shower is just Gravity fed the user will see and feel the water flow slowing down and hopefully would not remain in the shower to a point where there might only be Hot water flowing out.

    As I mentioned this is for possible future readers - but it should be how pipework is connected to any CWS Tank installation.


  13. Jim Goodenough

    Jim Goodenough Member

    Just one thing Wrighty8, you've probably thought of this though - please make sure you have good sturdy supports for the 2 CWS tanks with 18mm WBP ply or similar base that extends minimum 150mm beyond the base of the tanks in all four directions.
    • Agree Agree x 2
    • Informative Informative x 1
  14. Best

    Best Trusted Plumber

    Hi Chris,
    And the only thing I would add to that is the two storage tanks method adds to the risk of shower getting hot only water, if outlets are taken from separate tanks. Even if outlet to cylinder is drilled at higher level to cold outlet from other tank, there is a possibility that one tank will drain slightly quicker than the other, due to various worse case scenarios
    • Agree Agree x 1
  15. CHRISX

    CHRISX Active Member

    Hello again Best,

    I completely agree with your comments.

    Both for the reason that I described about the Cold supply pipework to a Shower Pump / Shower possibly being shorter and could be emptied quicker and because of the possibility that the Shower Pump might be drawing off the water from the CWS Tanks configuration quicker than the Tank water level can equalise via the pipework link.


    • Like Like x 1
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