Shower upgrade to 10.5kW

[fiskrond]

My plans have been thwarted due to foreseeable gas prices.. this has complicated things.
So.. I have decided that my best option is to go for an electric shower rather than running off the combi boiler.
There is already wiring for the long-deceased electric shower.. however it was pretty feeble in the winter anyway... 30A 6mm.. max 7.5kW.
The bathroom (ground floor) is being gutted anyway.. ceiling down.. whole lot. Also not too disruptive to lift floorboards through main part of house, so that's not really an issue.

From what I can gather the existing wiring for the shower from the main fuse box is 30A 6mm (see pic).. if I'm going to have an electric shower I may as well get a good one... 10.5kW.

Is it possible to simply change the 30A in the main fuse box to a 40A module and then run a 10mm cable on a like-for-like basis.. basically a 'system' upgrade?

 

[JohnW2]

My plans have been thwarted due to foreseeable gas prices.. this has complicated things. ... So.. I have decided that my best option is to go for an electric shower rather than running off the combi boiler.

Youy may want to think about that, since I doubt that we are going to see any major changes in the differential prices of gas and electricity - no matter how much it costs to heat (water or anything else) with gas, it willprobably continue to cost consdierably more to do the same with electricity.

In any event, unless there are teenagers (particularly female ones!) involved, showers are (should be!) so brief that the cost of heating the water is pretty trivial. A 5-minute shower with a 10.5 kW electric shower would probably cost of the order of 14p at current/recent prices, and appreciably less with gas-heated water.

From what I can gather the existing wiring for the shower from the main fuse box is 30A 6mm (see pic).. if I'm going to have an electric shower I may as well get a good one... 10.5kW. .... Is it possible to simply change the 30A in the main fuse box to a 40A module and then run a 10mm cable on a like-for-like basis.. basically a 'system' upgrade?

A 10.5 kW shower would need a 45A or 50A MCB in your consumer unit (what you call 'main fuse box'), not 40A. Depending on how it is installed (routed) the existing 6mm² cable (if that's what it is) might be adequate - an electrician could advise, and could also advise as to whether a suitable MCB would be available for your consumer unit.

If the MCB were 'upgraded' (and certainly if the cable were 'upgraded') then I think that most people would probably regard that as 'new work' (maybe even as 'new circuit') (rather than just 'replacement') which, in a bathroom, would be work that had to be notified to your Local Authority. That being the case, it would probably not be cost effective to 'DIY' it (if that's what you were considering), since the fee for the notification process would be £££ for you, but only a small handful of £ for a suitably 'registered' electrician ("self-certifying", which really means "self-notifying").

Kind Regards, John

 

[Vicario]

In my experience a 9KW shower is a good option. We have a Mira Sport which has summer and winter settings. It produces a good blast of hot water on both and never needs to be on maximum heat. We fitted a water softener to the incoming pipe and it was well worth the few extra pounds as it inhibits scale buildup in the water heating tanks (inside the shower). It's on a 40A breaker.

 

[ericmark]

I would love to move my showers from electric to the DHW supply, as far more controllable, although with a combi boiler at mothers house there was a problem with combi boiler as it had a small reservoir so starts cold goes hot then cold and then hot again, so easy to get caught out, and also the pump had to be removed to keep it legal. But most combi boilers can modulate 6 - 28 kW so you can select how much water is being used, but an electric has a fixed output. What ever size the heater is that's it.

But as @JohnW2 says the cost of running a shower is that low even if it did save money to in my case go from electric to oil heated water, then as a purely money saving it would never pay to swap, it would make sense to move from electric for better control, but can see no advantage moving to electric.

You don't seem to have RCD protection so would have to replace the MCB with a RCBO not sure if you can get a Memshield 2 RCBO so it could mean a consumer unit change, so on top of cost of shower unit also cost of CU so looking at over £500 could be £1000 that will buy a lot of gas.

 

[Vicario]

The main switch seems to be the rcd for all circuits.

 

[JohnW2]

In my experience a 9KW shower is a good option. We have a Mira Sport which has summer and winter settings. It produces a good blast of hot water on both and never needs to be on maximum heat. .....

We hear a lot of people (like the OP) complaining about the performance of 7.5 kW showers. However, although it is hardly ever used (basicallty exists only in case of failure of the DHW system), we have a 7.5 kW one (also Mira, I think - can't be bothered to look!) and I have to say that on the rare occasions I've tried it, it hasn't been at all bad.

Having said that, if one is going to have an electric shower, one might as well go for the biggest one that one 'reasonably can' - and in the OP's case a 9 kW one could well be a good compromise - because (with a 40A breaker) his existing 6mm² cable (if that's what it is) would almost certainly be adequate.

Kind Regards, John

 

[flameport]

an electric shower rather than running off the combi boiler.

Gas is still far cheaper than electricity.
A shower from the gas combi will be cheaper (both to install and use) and far better than any electric effort ever could be.

 

[JohnW2]

Gas is still far cheaper than electricity.

Indeed - although, as I said the energy cost of having a shower is so trivial (even with electricity) as to not really be a relevant consideration.

A shower from the gas combi will be cheaper (both to install and use) and far better than any electric effort ever could be.

I think most people would agree with that - assuming, of course, that the combi boiler is already installed.

Kind Regards, John

 

[fiskrond]

Lot's of info so far.. much appreciated!

The long deceased shower was a 'Berry' (no model number visible)... have a feeling that probably garbage when new.
Combi boiler is a Baxi Combi 80Eco.
I've got someone who will take care of the wiring (if required) as long as I lift the floorboards and pay for materials.. am owed a few favours for parts-only PC/Laptop repairs.
Is a small stone build terraced house c1860s.
I'm undecided/paranoid on the possibility of DHW failure and having an alternative electric source of hot water.. but I'm a single bloke and I can rough it if needs be.. kettle, bowl, flannel..

Welsh Water report: Static Pressure 18m-20m, 1.8/2 Bar, Flowrate 15Lpm at outsite stoptap.

Kitchen tap is say 4ft of copper pipe from combi.. very skorchio...
Bathroom water mebe 8ft total of copper pipe going down into concrete under hallway and resurfacing in bathroom.. there is a very noticeable loss of heat. Intention is to reroute pipework over top of door frame and come into bathroom at ceiling level.

I tried working out the kWh for heating water, external water pressure, internal flow rate, and then comparing electric vs gas.. aaand my brain fell over.

But I love learning stuff... and look forward to further advice! Again.. many thanks!

 

[flameport]

Combi boiler is a Baxi Combi 80Eco.

A 24kW boiler.
More than double the heat output compared to the most powerful electric shower you could fit.

 

[JohnW2]

I'm undecided/paranoid on the possibility of DHW failure and having an alternative electric source of hot water.. but I'm a single bloke and I can rough it if needs be.. kettle, bowl, flannel..

That's really similar to my situation as I described. All my usually-used showers are fed from (in my case, LPG-heated and stored) DHW, and I have one electric shower 'just in case' the DHW system ever fails -and for that purpose a 7.5 kW shower is fine.

So, I what I'm saying is that, if you want the reassurance/confidence that comes from redundancy, why not stick with combi-heated water (with the advantages that offers) for you primary shower, but have a 'back up' electric one available - which, if just 7.5 kW, could use your existing wiring and breaker?

Kind Regards, John

 

[scousespark]

("self-certifying", which really means "self-notifying").

Kind Regards, John

No it doesn't. If a person is on the Competent Person's Register the process is to certify that the work complies with Building Regs. Anybody else carrying out tasks, identified as notifiable, will notify LABC that they intend to carry out work.

 

[JohnW2]

No it doesn't. If a person is on the Competent Person's Register the process is to certify that the work complies with Building Regs.

Good to see you. I hope that all is well with you and yours.

I suppose what you say is literally correct, but I think we are essentially down to semantics here

Anyone who undertakes electric work who is not on the Competent Person's Register is also meant (per BS7671) to certify that the work complies with BS7671 (which effectively means compliance with the Building Regs, which say far less about electrical work than does BS7671). Hence anyone carrying out electrical work essentially has to 'self-certify' (compliance with BS7671), since someone who has not done the work cannot do that 'certification', whether or not they are a member of a CPS (or, indeed, whether or not thay are 'an electrician').

Anybody else carrying out tasks, identified as notifiable, will notify LABC that they intend to carry out work.

They will. However, the point is that, according to the semantics of Approved Doc P, when a member of a CPS undertakes 'notifiable work', the process of 'notification' (prior to the work being undertaken) does not actually happen - instead, the CPS member self-certifies (compliance with the Building Regs) after the work has been done. Approved Doc P calls this process 'certification', and does not require any other 'notification' in the case of work undertaken by a CPS member.

Maybe the people we're talking about should be called "non-notifying" electricians, rather then "self-certifying" ones - since, as above, strictly speaking anyone undertaking electrical work should ("self-") "certify"!

As you will probably realise, the main reason for my comment was that a lot of people seem to think that if work is not 'notifiable', there is then no requirement for it to be 'certified' (as complying with BS7671).

Kind Regards, John

 

[wundaboy]

Lot's of info so far.. much appreciated!

snip
I'm undecided/paranoid on the possibility of DHW failure and having an alternative electric source of hot water..
snip

When I do a house up (it's mostly been terraces with combi boilers) I've always followed the above principle of having two sources of hot water.

The electric shower I've always used which from my own experience is the best one available is this. It's never going to be a shower off even a 24kw combi, but I believe it's the best you'll get in electric.

 

[JohnW2]

When I do a house up (it's mostly been terraces with combi boilers) I've always followed the above principle of having two sources of hot water. .... The electric shower I've always used which from my own experience is the best one available is this. It's never going to be a shower off even a 24kw combi, but I believe it's the best you'll get in electric.

As I recently wrote above, I am a great believer in that sort of redundancy/'backup' - which is why I have an electric shower which is virtually never used.

However, as I also said to the OP, if the electric shower is only for that back-up purpose, it doesn't remotely need to be 'the best one can get". I would advise someone wanting such a backup to go for the cheapest one that could be easily installed - and, in the OP's case, that probably means sticking with a 7.5 kW one, so that absolutely no changes to his electrical installation would be required.

Kind Regards, John