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10.5kw Shower and Storage Heaters?

dandare1980
Hi,


I would be grateful for some advice regarding a potential electrical upgrade which I intend to get completed this summer when we have our kitchen and bathroom refurbished. I will engage the services of an electrician nearer the time, but wanted to explore some possibilities to help with planning the works.


A bit of context first - The property is a small ex-council 3 bed semi built in 1937 and most electrics appear to be from the 80s.


Everything is set up around economy 7 (no option for gas). Heating is delivered via 7 storage heaters, hot water comes from a cylinder with immersion element and the kitchen has a free standing electric cooker.


EON upgraded us to a smart meter when we moved in and fitted a separate non-adjustable time switch which activates the storage heaters via their own consumer units (2 in total).


The economy 7 night rate is active for 7 hours between 1:30 and 8:30 am in the summer, and 12:30 and 7:30 am in the winter.


The storage heaters collectively draw as much as 13.6 kw at peak. The 3 kw immersion is on a timer and generally used between 5:30 and 7.30 am, then a short boost 5:00 to 6:00 pm.


We don’t have a shower and would really like to fit a 10.5 kw unit when we upgrade the bathroom. This is where I have concerns – although our supply is rated at 100 amp, would I be in an overload situation if I was to shower when the storage heaters and immersion are all going together?


This is likely as we are all up and getting ready before the storage heaters switch off. Worst case scenario would be the storage heaters, immersion, hob plate and kettle are all going while the shower is active (other than these items we have very few other power demands).


I understand that principles of diversity may apply. In practice, when the storage heater circuits are first activated there is likely to be a big draw, but as we’re all in bed, by the time morning comes and we want to use the shower etc. most heaters will be up to temperature and only drawing intermittent power through thermostatic control. Of course, none of this is an issue in summer.


Should I instead consider a less power hungry 8.5 kw shower or do away with the idea and opt for better stored water and a pump (not preferred)?


Our current collection of consumer units (4) is a total mess so I will be getting quotes to have the lot upgraded. I am hoping it will be no more than 2 units, one for storage heaters the other for everything else.


I wanted to consider RCBOs instead of a dual RCD setup, but the cost may be prohibitive. I have thought about only applying the RCBOs to the main board, leaving the storage heaters protected by a single RCD. I have often seen showers on their own consumer unit but assume this wouldn’t be necessary with an appropriately sized consumer unit.


The electrician will need to install it all to meet regulation, so I may have no say in the matter on this point anyway.


Any advice or recommendations will be gladly received.


Daniel.

  • 0
    I knew that I had it somewhere, and now I've found it. The reference source that I needed about H.R.C. (high rupturing capacity) fuses. The book is "The Electrician's Guide" 17th Edition by John Whitfield. Third Edition. 


    Page 38. B.S. 88 part 2 fuses (which might be used as a main house fuse) according to the B.S., fuses rated at 63 Amps or less must NOT operate within one hour when carrying a current 20 per cent greater than they are rated at.


    For higher rated fuses operation must NOT be within 4 hours at the same percentage overload. The latter are required only to operate within 4 hours when carrying 60 per cent more current than their rated current.


    Z.




  • 0
    It is possible to put things like water heaters on a boost box or a relay change-over contactor so that they are on E7, but then clonk over automatically to the 24hr supply if the temperature drops and E7 is off. It is not often done however.
  • 0
    The high rated electric showers are often just too hot to use, "scalding" in fact, so many people only use them at a reduced heat setting anyway.


    They dont work by reducing the power input, they just increase the flow rate when the temperature is turned down.

    Thermostatic ones do the same. They will always use the rated current.

    A shower rated at just under 9kW is more than adequate in most cases.


    I've been very disappointed with 10.5kW showers, they should be 20% faster flowing compared to 8.5kW, but in reality it doesnt seem it. I fit on average 3x 8.5kW showers a week, and they are suitable for the majority of people. They are never going to be power shower pressures, but they are adequate for bathing.


    As for the power problem, I think it would be fine as it is. If you regularly shower after midnight, then maybe think about turning off a few heaters before showering. That is the easiest way to do it. A quick calculation shows the storage heaters, when on full power draw around 56Amps, a 8.5kW shower around 33 amps, so that'd be fine on a 100 amp supply.


    RCD covering 4/5 circuits against RCBO's. If your wiring is in good condition, then there is no reason why a split RCD board would not suit your requirements. 'Nuisance' trips are very rare,and usually traced to a faulty appliance. RCBO's are convenient, but at an extra cost. I'm happy with a split load board in my house.

  • 0
    Its overloaded, there will be the usual schemes such us contactors buzzing away keeping everyone awake, switching a few rads off while you have a shower, late at night, really? I am sure the kids are going to remember that..Its all electric, make full use of the tariff, use the Im heater with a mixer tap?. You are left with the radiator load and sundries.

    Regards, UKPN.Zap
  • 0
    Let's do some more sums! ?


    10.5 kW will heat 10500/4.2  = 2500 g water by 1 deg C per second.


    Assume that the input is at 10 deg C and the output at 40 deg C. Now we get 2500/30 = 83 g (or 83 ml) of nice hot water per second. That's 5 l per minute, which is enough.


    We have lived here for 20-odd years and I have never had a bath at home. (The things which one admits in a public forum! ? ) I prefer a shower to the extent that I will accept less than some people. 40-odd years ago we had a 3 kW shower. That was sufficient to get clean, but (especially in winter) not really adequate*. IMHO 6 kW would be adequate and 8 kW perfectly acceptable.


    *There is an old legal aphorism that consideration must be sufficient, but need not be adequate. In other words a contract requires payment (which could be a peppercorn even if the recipient does not like pepper) but the law does not require a deal to be fair to both parties.


    If you really want to know how much water is sufficient, ask a submariner! ?
  • 0
    More sums!


    10 min shower at 5 l/min = 50 l of water and 1.75 kWh of leccy. The leccy will cost about £0.30.


    The cost of water is difficult because the cost of sewerage is based upon water usage. Available figures online show wide variation. Nonetheless, if your water costs more than 0.6 p/l, it costs more than the leccy!
  • 0

    alanblaby:
    The high rated electric showers are often just too hot to use, "scalding" in fact, so many people only use them at a reduced heat setting anyway.


    They dont work by reducing the power input, they just increase the flow rate when the temperature is turned down.

    Thermostatic ones do the same. They will always use the rated current.

    A shower rated at just under 9kW is more than adequate in most cases.


    I've been very disappointed with 10.5kW showers, they should be 20% faster flowing compared to 8.5kW, but in reality it doesnt seem it. I fit on average 3x 8.5kW showers a week, and they are suitable for the majority of people. They are never going to be power shower pressures, but they are adequate for bathing.

     




    Hello Alan,

                        indeed the increase in water flow of the electric shower at a constant electrical input will reduce the water temperature and the opposite it true as well. Reduce the water flow and the water temperature increases.


    I was thinking of the Triton Enrich shower unit. The heating tank has two separate heating elements. Either one or both can be selected for heating, so you can get "half heat" or "full heating" of the water. So the current used is altered with this make of shower unit.


    Z.


     

  • 0
    I know someone who uses diversion on off peak a bit.

    I think most DNOs allow either 12 or 13KW storage heaters on single phase.

    He has a baby heater in bathroom (0.85KW) and to stop kitchen pipes freezing up diverts this heater to a fan heater in kitchen run by a relay and stat set to between 5 and 10 degrees. If that makes relays or contactors worthwhile on a larger scale I don`t know because for every KW you are doubling you are effectively twicing the charge time for each radial and that increases the cycling of storage heater stats thereby creating more peaks than the norm
  • 0
    Thanks to everyone for your responses and advice, it's really helped me to understand the situation better.


    I think for simplicity I'll press ahead with an 8.5 Kw shower, just to give me a few more amps of wriggle room.


    I've contacted Western Power and they're happy to send someone out to check the main fuse is rated at 100 amp (fingers crossed).


    I'm also contacting my supplier EDF to see if they can rid me of the smart meter - it hasn't been "smart" since 2015 when I changed provider. The setup with an external heating contactor is both messy and very noisy when it operates. The previous Landis + Gyr meter had an internal contactor and relay for the storage heaters which was silent in operation and much less cluttered.


    The shower priority devices are quite interesting, but hopefully an added cost I can avoid by choosing a lower rated shower.


    I want to stick with an instantaneous shower device Vs a stored solution, as it will require some fairly extensive tank upgrades otherwise.


    I'm getting the consumer units upgraded and as the shower is no more than 5 metres from this location the cost for installation shouldn't be too bad. If I opt for an unvented cylinder or bigger tank and pump, it's going to cost considerably more.


    Out of interest I observed the wattage draw when I got up this morning at 5.30 am via my smart meter's half-broken wireless screen. The storage heaters were active and the immersion had just come on timer. The draw ranged from around 2 Kw to 8 Kw peak, but the higher loads were only present for several minutes at a time.


    I'm hoping the electrician will be happy to fit all general circuits including the shower onto a 100 amp consumer unit with RCBOs. The storage heaters can be consolidated onto another 100 amp unit, but I might request a split dual RCD board to keep costs down - hopefully with a mix of heaters on each protected run so if a fault condition occurs in the middle of the night I won't lose all the heaters.


    Hopefully this approach won't see the Henley blocks, meter, contactor or main fuse overloaded - not for any considerable amount of time anyway.


    Thanks again for all the great advice.


    Daniel.

  • 0



    I'm also contacting my supplier EDF to see if they can rid me of the smart meter - it hasn't been "smart" since 2015 when I changed provider.


    Best of luck with that. I've not known anyone who has been successful with that. The companies are pressurised by government to fit them under threat of fines. They aint gonna want to remove them.



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