Shower set up - what is more efficient

artyboy

We have a new flat which is electric only - hot water tank with solid green foam lagging and 2 immersion heaters.

The current shower doesn't use the tank water, it's a Triton electric thing with just a cold feed.

We're in the process of renovating the whole bathroom, and it's got me thinking - is there a clear winner re efficiency in having the new shower also as an electric one, or taking hot water from the tank? 

Or are there too many variables with each option to suggest that one will generally come out better than the other?

Mr.Generous

Having a seperate electric shower will make it less likely you get stuck with no hot water to bathe, provided you have a bath, should something go wrong. If you heat the water tank daily all year then using that water to shower would be cheaper, if during summer months you don't heat the tank then I'd say elec shower cheaper.

QrizB

The flat has E7 or similar?

If it does, tank-fed will let you use cheaper electricity to heat the water for the shower. But a tank-fed shower is likely to have a higher flow rate than your instantaneous electric shower does, so you'll use more hot water. The savings will be rediced and you might even end up spending more.

Probably the cheapest option is to stick with the current style of shower and try to use it during the cheap rate period. This is easier if you're an early riser, and easier during BST.

Stubod

I would stay with your current set up....ie a shower that just heats the water when you need it..

Rodders53

Electric showers often have poor flow rates in the cold months.  Tank fed showers are similarly poor (and often poorer) unless the tank is mains water fed unvented HW type, as flats often have the CW tank atop the HW cylinder so there is little to no 'head' for the water.

A satisfying shower depends on the water pressure available!

Two immersions suggests that some form of off-peak electricity was/is available.  Green foam suggests a vented HW tank.  So it needs further investigation to check.  Changing to mains pressure unvented is not cheap.  

Probably most money saving will  be to stick with existing unless revamping the whole bathroom when changing to unvented HW may be more cost-efficiently done>

Scot_39

In terms of electrical and heat losses - energy efficiency - direct would almost certainly be better.
But I guess that's not really what your interested in but more  in terms of operating cost not energy efficiency.

Any water run from a tank will leave x metres of hot water and pipework - the x depending on flat plumbing layout.  In summer and quite a bit in winter that energy is just lost.

Not a massive share of hot water heating maybe but it will add.

In some properties with tanks with 2 heaters - one is often fed by off peak rate,  and the higher one often acts like a boost.  But that might just be to stop heating a full tank in your case.

How big is the tank ?
It may not be sized to support 2+ (the "we") full showers on just 1 overnight temperature boost,  if sized in tandem with cold fed shower
My tanks only c120l - could struggle with 2 showers and normal use - except mines is het 3x per day at off peak rates on my legacy e10 tariff.

And then others do make an effort to shower at off peak - whether you can time showers at off peak - in some regions e7 off peak ends 7 or 730 am GMT - so 8 am 830am in DST clock time.

So the cost of a shower - 10m 9kW shower = 1.5kW would cost 

On single rate - at c26p/kWh - 39p

On e7 maybe more like c14p 32p balance in some regions
E7 Night / Off Peak would be 21p
E7 Day / Peak - 48p

The tank would be similar pricing ratio for actual use, assuming your heating it anyway - plus any pipework losses in run to shower.

But tanks even the modern one's specs admit they will lose 1-2kWh per day when het to 60C.

So increasing the use would make the losses - useful heat in winter, waste in summer,  a lower percentage of total and arguably more bearable if worry to that level.

Others have stopped using their tanks to save that sort of 1-2 kWh loss per day (or worse on old tanks) - but I think it's worth it to know theirs hot water their and that my airing cupboard is damp free year round.

Shower Flow Rate vs Time - their is some study evidence for certain groups - higher flow rates reduce time in showers - and may even reduce water use for some.

You will probably find that unless money tight the main factor you might want to make decision on should be quality of the showering experience.

And for me flow / pressure matters.

But sadly I've looked at converting my cold fed shower - as its a pretty feeble flow rate if want it any sort of hot n the depths of winter - to tank fed in current place - but when I got quotes - the majority recommendation has been to go mains pressurised hot water - £1000s I just didnt want to spend - by time clear up the pipework in my loft space.  

There was a cheaper option - just connecting cold feed tank inlet to tank outlet - but that seemed a bit of frig (but it's actually what SG did to my parents when fitted the Combi boiler and took their header tank away).  

And if water pressure fluctuates with others in your flat or block and you stay cold fed (if someone runs a tap or flushes the loo) you might want to make sure you upgrade to a thermostatic protected shower, not stay with one of the cheaper manual electric if thats what is currently fitted.

wrf12345

Have a look at YouTube videos on the benefits of taking a cold shower each morning and consider not heating water at all, nice gesture to our greedy energy companies...

GingerTim

wrf12345 said:

 the benefits of taking a cold shower each morning and consider not heating water at all

Life's too short.

MattMattMattUK

A hot water tank on E7 or an EV tariff will be a far better option than a heat on demand electric shower provided you have decent water pressure. What is the EPC of the flat, well insulated, what kind of heating do you have? I have a very well insulated flat so I rarely need to use the heating even in winter, I have a large hot water tank and heat that on an EV tariff at 7p per kWh so roughly comparable to gas. 

Ildhund

MattMattMattUK said:

A hot water tank on E7 or an EV tariff will be a far better option than a heat on demand electric shower provided you have decent water pressure. 

I'm not sure that statement's always accurate. In a typical use case, an electric shower will heat and deliver about 30l and use something like 0.8kWh each time. Most hot water tanks contain enough for many showers, but using E7 to keep it heated up will consume far more than what's needed for a couple of showers each day. If the immersion heater's in use anyway (for what else?), then it might make sense, but I'd certainly do some sums before committing to an expensive plumbing job.