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power shower... or dribble?

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power shower... or dribble?

Old 24th May 2022, 17:20
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power shower... or dribble?

I'm in the lucky position to rent out 2x 1 bedroom flats in the same building. Right now both have an electric immersion heater in the cupboard next to the consumer unit, this supplies all the hot water. Back when I lived in the one of the flats it drove me nuts to have to turn on the immersion an hour before wanting a shower, and heating a tank of water. Now with electric prices the way it is it must be awful for my tenants. There's no gas in the building,

So I fancy replacing the tank with an instantaneous 10kw electric water heater, heats water from cold as there is demand. But I'm loath to lose the full on power shower experience that's there now. Anybody have any experience of a whole house electric heater? I'd rather not install an electric power shower as it's a lot of wiring. One flat has a single man, one a married couple so I'm not fussed about temperarture fluctuations if somebody else turns on the hot water in the kitchen for example. Room heating is by electric panel radiators. They're 3 floors up so no chance of ground/air source heat pumps etc. My theory is get their electric bills down and they're more likely to stay as renters and be easier to let out in the future.

Simon

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Old 24th May 2022, 18:11
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Interested in this Simon - I have a similar situation and set up with two tenants - immersion heater for all hot water except one flat has the instantaneous heater under the sink in the kitchen - both have rather weak electric - 6kw showers - ie dribble at best
I would like to update for their benefit also
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Old 24th May 2022, 18:22
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My daughter's married quarter has an electric power shower, I would describe the output as akin to a warm mist rather than a decent shower.
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Old 24th May 2022, 19:28
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10kW shower running at mains water pressure (no pressure/flow boost) is quite adequate without being exciting.
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Old 24th May 2022, 20:57
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I understand that heating and hot water bills are 'cause celebre" in the UK at the moment.

Go ahead and spend your money buying and having installed a new hot water system that will save, what", 10 or 20 or even 25% cost in energy. Basically all you have done is transferred your tenant costs to yourself. Way to go.
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Old 24th May 2022, 22:17
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Originally Posted by DType View Post
10kW shower running at mains water pressure (no pressure/flow boost) is quite adequate without being exciting.
Agreed, but upgrading to one often means upgrading the usual 6mm cable to 10mm, which can be a faff.

CG
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Old 24th May 2022, 22:29
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Dont Brits have a shower once a year?
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Old 25th May 2022, 06:43
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Originally Posted by ChrisJ800 View Post
Dont Brits have a shower once a year?
Where I live, we have showers 300 days a flippin year!

CG
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Old 25th May 2022, 07:00
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Originally Posted by charliegolf View Post
Where I live, we have showers 300 days a flippin year!
What? Your're trying to tell me that S Wales only has 65 days a year of continuous rain? I'm sceptical...

Not withstanding the wiring faff, a 10kW electric shower will have by far the cheapest running costs, and the latest ones are surprisingly good. I'd ask your tenants how much they value economy over getting a really good shower. When I used to rent the showers were universally terrible; I suspect that a 10kW electric job will put you ahead of most of the rest of the market.

Worst shower I ever had in a rented flat was the gravity-fed one from a header tank at head height :-(
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Old 25th May 2022, 07:26
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I used to have a very nice 2 bed flat down in sunny sussex,the only thing I hated about it was the shower 'pump' which never really worked,I put up with it for a couple of years (no money) then luckily got to know a couple of guys at work - one who did a bit of plumbering on the side and the other (who was a sparky) who did house electrics on the side.
The 'plumber' came one morning with the longest drill I had seen up till then to drill through the wall from the fuse cupboard to the bath wall and between us we mounted the elec shower (10 kw ?) and pushed the heavy wiring through to the fuse board,the leccy came over in the afternoon and upgraded the fuse board to be a CB board and connected everything up - as others have said - a very capable shower.
A couple of years after that another mate fitted an on demand gas heater in the kitchen which meant I could get rid of the huge immersion tank and have some more cupboard space

One thing I forgot to mention - when I looked under the bath to remove the old 'pump' wiring I found that whoever installed the wiring (early 1980's built) had just left it on the floor with a non waterproof terminal block connecting to the actual 'pump' wiring - placed right under the bath drain and associated pipes - good effort
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Old 25th May 2022, 07:28
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Originally Posted by pasta View Post
Worst shower I ever had in a rented flat was the gravity-fed one from a header tank at head height :-(
That was one of the problems in my flat mentioned above - it was a top floor flat with the immersion/hot water tank mounted on the floor of the 'airing cupboard' - result next to no hot water pressure LOL
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Old 25th May 2022, 08:48
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CG
Agree, but I cheated.
Ran one cable in conduit up an outside wall from under the ground floor to the attic.
Another time, I dropped a cable down the cavity wall (before it got filled with insulation). Not sure that one is legal, though a professional did think it was a smart move!
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Old 25th May 2022, 09:23
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I had a 10kW, 2 phase inst. electric whole house HW heater. It was done this way in Australia in the 50s; I bought the house in the 70s. It wasn't adequate and I replaced it with gas, these days I'd go heat pump. That doesn't help because neither is available to you. Just don't expect much from the inst. electric heater.
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Old 25th May 2022, 10:27
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Originally Posted by DType View Post
10kW shower running at mains water pressure (no pressure/flow boost) is quite adequate without being exciting.
A bit of quick maths suggests you'll either be running around to get wet or getting cold.

Heat input: 10kW = 10kJ/s
Heat capacity of water = 4.182kJ/kgC
Change in temperature of water = 10kJ/s / 4.182kJ/kgC = 2.4 kgC/s

Either decide the flow rate to determine the resultant temperature change or decide the temperature change required to decide the flow rate.
A typical household or garden tap running flat out delivers about 15 litres a minute. A quick google tells me that in Australia in new homes the shower is not supposed to flow more than 9 litres/minute and that 7.5 litres/minute is common.

Let's go with a very conservative 6 litres/minute = 0.1litres/second = 0.1kg/second.

2.4kgC/s / 0.1kg/s = 24degC temperature change.

Start with water at say 10degC, that gives you a 34degC shower, barely luke warm. (A bit more googling tells me that a comfortable hot shower is about body temperature or slightly higher, so around 40degC)

I would think about a 20kW instantaneous hot water heater would provide an adequate shower; offering 4.8kgC/s, enough to heat 9 litres/minute up by 32degC. Even that might be a bit feeble if your water starts close to freezing...

I'd been meaning to get around to a calculation like this for a little while to determine how big a propane instantaneous hot water heater was needed for portable hot shower. Here are the (abridged) specs for one such unit, to check my numbers are somewhere near reality:
Fully adjustable temperature with a maximum of 50C
The constant water flow of up to 8L/min
Total nominal gas consumption: 28MJ/h
Maximum water temperature: 50C
Flow rate: 480L/H


8l/min = 480l/h = 0.133kg/s
28MJ/h / 3600 s/h = 7.778kJ/s (kW)
7.778kJ/s / 4.182kJ/kgC = 1.86kgC/s
1.86kgC/s / 0.133kg/s = 14degC change in temperature.

The system may be electronically limited to 50degC, but it needs to start with water at 36degC (or to flow much less water) to get there.
Can't honestly say I'm surprised. Running at 4 litres/minute it could get from 12degC to 40degC, a more realistic temperature change required for a shower.

Last edited by nonsense; 25th May 2022 at 15:08.
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Old 25th May 2022, 10:38
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I am always very nervous about electric showers: standing underneath the water, completely wet from head to toe with mains electricity flowing through the heating element in the heater tank on the wall next to me, and wondering who installed it and how much care they took and if it was properly tested and verified........You absolutely must get it checked 100% that the electric shower is properly and correctly earthed in the bathroom with the correctly sized cable etc.

I had to replace an electric shower which stopped working, and out of curiosity took it apart, only to find that the earth wire inside had only been half crimped onto one of the terminals, so not a good enough connection.............

The OP might be better buying a programmable timer, capable of switching the immersion heater load (up to 13 amps) to operate the existing immersion heater in the cylinder. No plumbing required for that, (although a "sussex" outlet flange on the cylinder would be good idea to prevent one shower stealing hot water from another).
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Old 25th May 2022, 12:20
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When travelling in Bolivia some years ago the showers tended to be a heating element in the shower head. Some of the installations were, shall we say, dubious.
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Old 25th May 2022, 12:26
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I am afraid that my old system is prone to dribbles.
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Old 25th May 2022, 12:27
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Uplinker
We have “Rain showers” but they need a pump to supply enough water to make them work. As we do not pay water bills in UK as we have spring water and septic tank I think the power required and cost is nominal and no issue. My apartment in Munich has a mixture of rain shower and power shower but again require pumps but I can not say they seem that expensive as the heating / AC in the Apartment are considerably cheaper than heating an old farm.

As for showers v bath I cannot remember my last bath !

Cheers
Mr Mac

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Old 25th May 2022, 14:24
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Join Date: Apr 2007
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You need to consider many items – water pressure, water useage, power available.

If you’re on a metered water supply then a traditional pumped supply off a hot tank will easily consume loads of water. An electric shower fed by mains pressure is likely to use much less water. Few electric showers will supply the type of rainfall shower head c300mm diameter that is so popular these days.

A 10.5kW shower can only ever supply that much heat to the incoming water. In UK incoming mains water temperature will vary greatly according to the season. 10.5kW heating in the summer will give a good hot shower at a good flow rate (although not generous enough for a true rainfall shower head). The same shower heating water in the winter will still give you the same outlet temperature but at a far reduced flow rate.

The old 6.5kW showers really struggled to get much more than a dribble in the winter but customers were happy when I fitted them in the summer!

Electrically you’ll need at least 10mm2 supply cable for a 10.5kW shower – maybe 16mm2 depending on length of run and amount of insulation you run through. The larger 10mm2 cable may not fit within the terminations in the consumer unit or shower isolator. 16mm2 will certainly be a struggle. Some older consumer units may not take larger loadings of 40 amps plus. Any new shower should be supplied from a circuit protected by an RCD. You may need a new one fitted.

If you’re really unlucky you may need an electric pump to boost low mains pressure in a block of flats to an acceptable level for the electric shower.

The plumbing’s the easy bit; you need a qualified sparks for the rest. I’ve lost count of the number of burnt out, overloaded shower circuits and accessories I’ve seen.
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Old 25th May 2022, 18:57
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Cremegg
Thank you on behalf of others as that was very well explained, and may help in some people with their decisions re plumbing and showers.

Cheers
Mr Mac
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