On 28/04/2019 13:36, David wrote:

This has been somewhat covered in a couple of recent threads but they are
long so I'm trying to pick up on a few points.

(1) The maximum power output of a UK electric shower is around 10 kW. The

There are some at around 11kW

output of a small(ish) combi boiler is around 28 kW. So the combi should

24kW is a common size for a small one.

be able to apply 2.8 times the heat to incoming cold water and so (I
assume) heat 2.8 times the amount of incoming water to an acceptable
temperature compared to the electric shower.

Pretty much - it a linear relationship. See the table he

http://wiki.diyfaq.org.uk/index.php/...ting_the_Power

(2) Electricity costs around 3 times gas (per unit of energy) which kind
of balances out. You can either have about 3 times the hot water in your
shower for the same price or save money each time you shower at lower flow
rates.

I think most people would go for the more satisfying shower which does
reduce/eliminate the cost saving from using a combi boiler.

Probably... Still there are plenty of people happy with the performance
of their electric showers. They also have some advantages like being
less affected by people running hot water elsewhere in the house.

{Wanders off into speculation}

Hmmm....what is the maximum (ignoring wiring restrictions for the moment)
that you could get out of a UK domestic 2 phase supply?

Do you actually mean 2 phase (since that is not a common option). Single
phase or three phase would be a more common choice.

For single phase with a 100A incomer, about 24kW total.


Simplistically, using (Volts * Amps = Watts) and rounding outrageously 4
amps = 1 kW.

So again rounding outrageously a 13 Amp circuit could support a 3 kW fire,
for example.

Yup.

If your mains incomer is 60 amps (a lot go up to 100 amps) then you might
be able to draw (60/4) = 15 kW is nothing else is powered up, or (100/4) =
25 kW for a 100 amp supply.

Yup.

I realise there are all sorts of minor (hah!) constraints but if you had a
100 amp incomer then is there any reason that you couldn't (with some very
thick cabling) take 60 amps for a shower giving you 15 kW of toasty
goodness?

You could...

Perhaps pairing up a couple of lower powered showers in parallel,
feeding a common shower head.

I do note that taking all the output from a 100 amp incomer still gives
you less heat input than a combi boiler.

Keep in mind you can vary the demand dramatically by variation of she
spray pattern, and jet size, as these will have a large effect on the
actual flow rate required.

3 phase electric shower, anyone?

Here you go:

https://www.aquahot.co.uk/zip-dbx24-...er-heater-24kw




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/