Advice on shower over bath replacement

Discussion in 'Plumbers' Talk' started by JimDC, Nov 11, 2016.

  1. JimDC

    JimDC New Member

    First time buyer and first time poster so apologies if info is missing.
    I'm looking to replace the taps on the bath to include a shower head. Currently we have a low pressure water system (cold water tank in the loft, immersion heater in main bedroom cupboard) and what seems like great water pressure coming from the bath taps.
    Current shower is a plastic unit clipped onto the taps with a switch for tap/shower head control. The shower is pretty useless, hence the need to replace.
    My ask for advice is whether simply changing the taps to a built in tap & shower head type would be likely to improve the flow from the shower? Or, should I forget that and go straight for a power shower?

    Thanks in advance for any advice or assistance, if you need any further information please let me know.

    Attached Files:

  2. wiggy

    wiggy Screwfix Select

    All the plumbers are in the pub mate
    JimDC likes this.
  3. Joe95

    Joe95 Screwfix Select

    You gotta wait till they appear, usually one comes out of hiding early morning or midday.
    JimDC likes this.
  4. Joe95

    Joe95 Screwfix Select

    As you mentioned water pressure is good coming from the taps, you would likely get away with the mixer shower/bath tap combo. Don't mix up flow and pressure though.
    An electric shower would need sustained pressure and flow, which you would likely have with tank fed system. However, you would have to get one suited to your water pressure. An electric shower also uses an incredible amount of energy and you will notice the difference in the electric bill. If the shower is simply being replaced because it is a 'bodge' (lets face it, that is) then you should already have the pressure behind it. An alternative is to use a shower pump before the mixer tap to improve the pressure that the water flows, note it will not increase the flow. This will be cheaper in the long run. I removed the electric shower when re-fitting my bathroom, and installed a shower pump before the bath taps. It provides better pressure to the water and gives the shower some 'life', so to speak.
    JimDC likes this.
  5. G&W Plumbing & Heating

    G&W Plumbing & Heating Active Member

    You need at least 1mtr of head which even then is poor. Fit a shower pump but you need to modify pipe work
    JimDC likes this.
  6. Jim, you say the flow coming out the taps is good? Cool. But that's at 'tap level'.

    See when you turn on the shower, well hold the showerhead also at tap level and check the flow (you could fill a pan for 10 seconds and measure the litres) and then repeat this with the showerhead held at its working height - which is above yer 'ead. Again, measure.

    That'll give you some idea of the likely success. I suspect it'll be little...

    Mira make (made?) an Excel model thermostatic bath shower mixer, and if ALL the flow restrictors (including the non-return valve on the outlet!) are removed, then it'll apparently handle down to 0.1bar pressure, which I reckon is as low as it gets.

    Even then it may struggle without pumps - it all depends what your tests above indicate.
    JimDC likes this.
  7. JimDC

    JimDC New Member

    Thanks Joe, G&W and D.A. I'll give it a test and see what comes out at head height.
  8. Joe95

    Joe95 Screwfix Select

    Ah, as usual DA comes in and provides a more detailed answer and more useful information
    What a way to make our answers look useless! :D:p

    Yes head pressure is important and the tank would have to be rather high up to supply an electric shower. As G&W suggested, much better luck with a shower pump. See how you get on with DA's suggestion on testing pressure
  9. Ok, time for me to stop paying you...

    (But, thanks :) )
    G&W Plumbing & Heating and Joe95 like this.
  10. JimDC

    JimDC New Member

    So I took your advice (thank you once again!) and measured flow rate for the shower and the taps, details below if they help illustrate the problem/ a solution?
    I set the shower to a comfortable temperature at head height and switched between shower on or taps on for my testing:

    1 litre every 3 seconds from the tap unit itself
    1 litre every 18 seconds for the shower at head height with the shower head fixed on
    1 Litre every 12.5 seconds for the shower at tap level with the shower head fixed on

    Without the shower head attached I get 1L in 11.5 seconds at head height or 8 seconds at tap level

    Not quite sure what to do with these stats but they suggest to me that the rate of flow reduced by the increase to head height is higher than any change in the shower unit itself without the flow rate/pressure being increased.
  11. What those stats tell you is that you will have a miserable shower from your existing set up.
    You have three options:
    Shower pump
    Electric shower
    Unvented cylinder
    The last one is a complete curve ball so forget it.
    Shower pumps are straightforward to install and you'll get lots of hot water - until the cylinder empties.
    Electric showers are straightforward to install on the wet side but can be problematic on the sparky side but you never run out of hot water.
    Take your pick!
    JimDC likes this.
  12. Pollowick

    Pollowick Screwfix Select

    One quick, temporary fix might be to look at the shower hose bore. Some are quite fine and if yours is such then it will restrict the flow.
    JimDC likes this.
  13. If the cold water storage tank in the loft is sitting on the ceiling joists then you have 300mm head to your shower. Even with a 100mm hose you'll still have rubbish flow. Ye canna argue with physics captain!
  14. Joe95

    Joe95 Screwfix Select

    Which is why a shower pump may be the best option, finding an electric shower that is optimised to work at such Low pressure will be fun...
    JimDC likes this.
  15. Pollowick

    Pollowick Screwfix Select

    I know that but just look at the comparison of tap flow to shower hose at tap level - it is around 1/3 suggesting that there hose is constricting, reduce that if possible and at least the flow at head height might increase a little.
  16. Joe, you don't run an instantaneous electric shower from tank cold. It's off the mains.
    There's another option, you could use an electric shower that has an internal pump, 3A demand, and utilises the existing tank H & C.
  17. Joe95

    Joe95 Screwfix Select

    Makes sense. I was thinking about pressure, not amount of water the shower would use.
    Proabably a good thing I've never installed one new then!:D
  18. But Joe, people come on here asking for advice yet you proffer an opinion even though you don't have any knowledge. How does that sit with you?
  19. Hi Jim.

    Comprehensive testing there - well done!

    I wish I could say it tells us everything we need to know, but as pointed out above by the likes of Pollo, it' doesn't - quite.

    Back to basics - you said in your OP that the 'pressure' from the taps was 'great'. It isn't.

    What I mean is, the flow from your taps may well be good (and you've chust confirmed it is at a nice 20lpm) but the actual pressure behind this flow will be pants - you could stop the flow easily with yer thumb, for instance.

    The pressure is pants because that is typical of vented/stored systems like yours. There's nothing wrong with that, but it's why the pipes going to your bath taps are 22mm wide - when you have low water pressure, then the pipe size is important.

    Also, as soon as you raise the water outlet, the flow will fall away dramatically (as the outlet gets closer to the actual height of the water store - where the water is actually coming from - then the pressure and flow will fall away. When your hose is at the same height as the CWS in t'loft, the pressure will be zero - and so will the flow).

    You've done a good check here by comparing what the flow direct from your taps is to that coming from the attached shower hose at the same tap height (and with no shower head). The water flow from the shower hose at tap height falls from 20lpm (taps only) to 7.5lpm (from the shower hose at tap height). That is a very dramatic fall, and suggests that the nasty shower attachment you currently have is really restrictive.

    That in turn suggests that if you were to fit a good quality bath shower mixer unit (like the Mira Excel BSM), then your flow at head height should be a lot better than what you currently have (a paltry 3.3lpm - which is worse than an electric shower!).

    But the problem is that we cannot guarantee that from here...

    Ok, your choices are:

    1) Check where your cold storage tank is in the loft - is there any chance of lifting it higher? You might not need to, but it would be good to know it could be done if needed. Or is it already as high as it can realistically go? If your tank could go higher, then if I were you I think I'd risk a Mira Excel BSM (provided I bought it for a lot less than the RRP of £600-odd!). I got one for my bro recently for around £175 on eBay, brand new. But that was lucky...

    2) If the tank cannot go any higher, then it's a tougher call. You could still risk a bath/shower mixer but be prepared to fit pumps to the hot and cold supply - this will likely come to about a further £300 or more. It might not be needed, but it could be...

    3) That's your bath/shower mixer options taken care of, I think. Now you need to look at separate shower units, and a really cracking option is an electric pumped unit. These look exactly like electric 'instant' showers, but have a wee pump inside which usually runs on low voltage with a mains transformer mounted elsewhere - under the bath or in the roof space. These give a really great shower and are cheap to buy and install.

    4) I personally wouldn't go 'instant electric' showers as they are pants (although fractionally better than what you currently have!)

    The Mira Excel is very expensive, but if you rip out all the restrictors inside them it can apparently handle right down to 0.1 bar pressure, which is probably not far from what you have. If you want to look for a cheaper alternative, then you'll certainly need one that'll go down to 0.2bar, and it'll mention that it's suitable for 'gravity' systems.

    It's tricky to know whether the huge drop in flow when you use your shower attachment is down to it being restrictive or chust you raising the hose end up to the proper showering height. It would be useful to see what the flow would be like with an unrestrictive hose on there... And chance of getting hold of s short length of normal hose and holding it tight directly against a bath nozzle - even use tap as a temp measure! Then hold the other end at 'head' height and try the flow test once more.

    If this turns out to be significantly better than the 7.5lpm from your current hose, then it could be promising. (Bearing in mind you'd only be testing one bath tap at a time. Test both...)

    And please report back as to the location of the CWS in t'loft.
    Last edited by a moderator: Nov 15, 2016
    JimDC likes this.
  20. Joe95

    Joe95 Screwfix Select

    If you read my earlier post, I offered advice based on my knowledge. Which is far from 'none' but also far from a professional plumbers. Although not well explained, it gives an idea.

    An instant electric shower could, in theory, be installed to a tank fed system. I have seen it done, and with reasonable tank height, this can work. It also depends on what is setup to refill the tank. I know of functional systems setup in such a way the electric shower does not drain the tank.

    I have also replaced showers with internal pumps,and replumbed them to the mains supply after air has been introduced to the pipework and destroyed the pumps.

    Regulations would require an electrition to install the power for an electric shower, as it is classed as a 'new circuit' and would therefore add large costs.

    As for sitting with me. It does not bother me. As you said 'people on here are asking for advice' therefore I offer advice based on the knowledge I have, of which is not at a professional level, but good. I am also on here to learn things too, and by offering my advice and then listening to constructive criticism and resoning, I can broaden my knowledge. I am open to your constructive criticism, not your accusation of 'no knowledge'.

    Lighten up a little :) you are being too 'resistive' to other people's ideas, I'm sure it is not to do with the 'Ohm' in your name. Yes I also have terrible puns
    Last edited: Nov 15, 2016

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