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Unvented: What post installation changes should I make or "If it ain't broke.."

Discussion in 'Plumbing and Central Heating' started by David Costelloe, 25 Jan 2021.

  1. David Costelloe

    David Costelloe

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    Should I change out all the old low pressure taps and valves after going unvented?

    I recently had an unvented cylinder installed. Our pressure is around 3bar and max flow rate via a water softener is c. 20l per minute. It's on the limit and one day we or the next owner's will have to bite the bullet and upgrade the capacity of the mains feed. But for the three of us, it should be OK.

    Previously most of the hot cold/taps, toilets etc were fed from a large water tank installed in a bedroom cupboard, providing little gravity pressure for the top floor bathroom - this was offset by the use of gigantic imperial pipes (40+mm), so the flow rates were perfectly fine. And the flow to the middle floor bath was the fastest I'd ever seen (bath filled in a couple of minutes).

    Now, post installation, the flow rate to the bath in the top floor bathroom is similar, but we now have a thermostatic shower that is excellent.

    The old restored Mira 8 shower (c 1964) on the middle floor runs beautifully, and you can run the two showers at the same time without a large impact on flow rates. The middle floor bath, fed by these big pipes, when running on its own is similar to the top floor in flow rate. However, this outlet is "greedy", and if running at full pelt, starves the upstairs outlets if you try to use them.

    After the change, two of the toilet float valves leaked and needed to be changed to high pressure variants. I've tested the impact of flushing the toilet on the Mira shower and there is little change in flow rate and no unacceptable change in temperature?

    So, is it worth doing any of the following:
    - Put bigger hoses on the water softener?
    - Change out/put restrictions on taps designed for low pressure supply? Would this reduce the middle bath's "starvation" of other outlets?

    I'm tempted to replace the Mira 8 with a thermostatic shower - but it is disruptive and I like the idea of having a well regarded old shower valve.
     
  2. rbranco

    rbranco

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    If you do not need the pressure just the flow rates to taps etc you could look into PRVs, might be cheaper than replacing all the taps.
     
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  4. MeldrewsMate

    MeldrewsMate

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    Yes, put larger (high flow) hoses on the softener.

    Your supply rate, by modern standards, is remarkably good at 20 litre/minute. What you are experiencing is a nuance of any unvented water system, that the maximum total water flow is only that which the mains can deliver. Previously you had this wonderful buffer store of water which allowed water to be used (albeit temporarily) faster than the mains could deliver. There were problems with interaction between outlets both then and now, just of a different type!

    Rejoice in your shower performances, and take fewer baths!
     
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  5. Madrab

    Madrab

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    The larger bore pipes, by their very nature, will always steal as much of the flow and pressure they can when in use. That will always reduce the dynamic rates that the upper floor has access to unless there is 3bar dynamic mains pressure.

    You say you have 3 bar, how well does the mains sustain that pressure when multiple outlets are being used? If you have enough flow capacity to the upper floor outlets (they work fine on their own) then it must be the pressure that's dropping off when the outlets on the larger bore pipework are being used.

    I'd be tempted to gauge an outlet upstairs and check the dynamic pressure drop when the floor below is being used, you may find the pressure drops off rather sharply. If you find that's the case then the large bore pipework may need replaced to bring some balance back into the system.
     
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