6kW hot water cylinder

[AndyPRK]

John. While I can understand you arguement for not having a bath/sink switch on an E7 system, it doesn't really apply here because:
1. This setup isn't on E7 so it doesn't matter if it was left on 'Sink / upper'
2. Both heaters are the same size.

In fact one could leave it on Sink, to get some economy out of the system if the op was living alone. And should they want a bath, could switch it to bath!

Simon, cleaver idea about using the stat output.
I expect those shower priority switches cost £100, so the OP would not save £100 in electricity having one.
But if a cheap relay system were available it would be interesting to consider. (but probably not very economical on electricity)

The options I see are.

1) A dual or 32A supply to the tank area
2) A sink/bath change over switch
3) 2 dual pole switches, with a simple label saying don't turn both on at the same time. (I guess the MCB would trip and be annoying) These fed from a timer or 1 fed from a timer and one as backup
4) A timer with boost function. The timer feeding one element and the boost feeding the other. This could be connected either way round.
These are the ones I like.
https://www.tlc-direct.co.uk/Products/SMTRTM7.html
and won't allow both elements on together


The way I see it, for the cost of a switch, it would be a great shame not to have the ability to turn the 2nd one on, if the normal one fails

 

[JohnW2]

John. While I can understand you arguement for not having a bath/sink switch on an E7 system, it doesn't really apply here because:
1. This setup isn't on E7 so it doesn't matter if it was left on 'Sink / upper'

Why not? If one switched it to 'upper' and then forgot to switch it back to 'lower', then one would subsequently never get a full tank of hot water unless/until one remembered to change the switch position.

2. Both heaters are the same size.

You give that as a reason for "it not really applying here", but I can't see that it would ever be relevant 'anywhere', with or without E7. Apart from anything else, maybe I've missed exceptions to this 'norm', but I have personally never seen any standard domestic HW cylinder with two immersions which were not both of the same 'size' (power) - have you?

As I've said, I really can't see the point of the upper immersion, with or without E7 (other than as a 'spare') - since,as I have said, switching on that element has essentially the same effect as would switching on the lower immersion for a limited period of time. If one can trust oneself to remember to switch it off after that 'limited period of time', then a simple manual switch would suffice. If one can't trust oneself (i.e. might leave the lower immersion 'on' for a long period', then some sort of 'lag switch' ('boost switch'), as mentioned above (maybe as a function of a timer), could be used to switch it on for a pre-determined period of time.

What point do you see in having the upper immersion (except as a 'spare, in case the main/lower one fails!)??

Kind Regards, John

 

[AndyPRK]

If one were to leave it on sink with an E7 system, one with be rather annoyed at having to pay peak rate electricity prices to heat the full tank.
Clearly this doesn't apply without E7, and is just a minor annoyance of having to wait 30 mins or so.

I've seen vented cylinders (with dual vertical mounted immersions). It basically fits into the same hole as a standard one. It has a long (standard) element, and a short element (lower power), that only heats the top half.

Clearly the manufactures see a reason to fit a second immersion as standard on bigger tanks. They would not go to this extra cost for no reason!
I could guess the reasons maybe:

1) There is a building regulation requirement that tanks must heat up in a certain time. Providing 2 elements enables compliance with this


If the op lived on there own, and didn't take baths, and used peak rate electric, I would consider it more efficient to only use the top element.

 

[JohnW2]

If one were to leave it on sink with an E7 system, one with be rather annoyed at having to pay peak rate electricity prices to heat the full tank.

True - but that still doesn't explain why one needs the 'sink' (upper immersion) facility in the first place.

I've seen vented cylinders (with dual vertical mounted immersions). It basically fits into the same hole as a standard one. It has a long (standard) element, and a short element (lower power), that only heats the top half.

One of my cylinders has one of those - but it's exactly the same as if I had two separate immersions (both are 3 kW) - just a way of doing it if the cylinder only has a single, top, immersion boss.

Clearly the manufactures see a reason to fit a second immersion as standard on bigger tanks. They would not go to this extra cost for no reason!

It's not them that are paying the 'extra cost' - in fact, it probably increases their profit! You'd have to ask them the reason they do it!

I could guess the reasons maybe:
1) There is a building regulation requirement that tanks must heat up in a certain time. Providing 2 elements enables compliance with this

I dont think so ...
1...I am unaware of any such regulation.
2...If it were to stand any chance of achieving what you suggest, both immersions would have to be powered simultaneously, which everyone here seems to be saying is not an intended/'normal' mode of action.
3...I doubt that it would actually speed up heating all that much. Once the lower element had heated some water, it would rise to the top, and that would cause the upper element's thermostat to turn it off. It would work if the two 3 kW elements (and their thermostats), or a single 6 kW one, were at the bottom, since neither would then be turned off by their thermostats until the temp at the bottom of the tank was up to the desired temp (i.e. the cylinder would be full of hot water).

If the op lived on there own, and didn't take baths, and used peak rate electric, I would consider it more efficient to only use the top element.

... or, as I keep saying, use a time-switch to switch the bottom element on for fairly short periods.

I still struggle to see any real point/value in having elements 'top and bottom' - maybe someone can help me?

Kind Regards, John

 

[SimonH2]

I still struggle to see any real point/value in having elements 'top and bottom' - maybe someone can help me?

If on single tariff, I'd agree - no point. However, there's an argument that (from the manufacturing and distribution PoV) it's not worth doubling your SKU count to provide single immersion units for single tariff customers, and double immersion units for dual tariff customers.
For those using electric only heating and who have E7 like tariffs, then heating the whole tank off peak is the only sensible way to operate it. For those occasions when you "run out" of hot water, having the upper immersion makes sense to heat only the upper part of the cylinder. It's notable that when I've been looking at thermal stores, electric-only models seem to have two immersions, while all those with other heat inputs have only one - which would fit in with that, who would have an electric-only cylinder if they had the option of other heat sources ?
To many of us these days, the idea of "putting on the immersion" in advance of having a bath is but a quaint memory of something our [grand]parents used to have to do. I imagine most youngsters these days have never experienced anything other than "constant hot water".

As an aside, a while ago I went on the tour round Chatsworth House. At one point, on a back stairs landing, I spotted a large panel with quite a few sets of switches and indicator lights. For each room fitted with it's en-suite (and some of them were quite clever in the way they'd been fitted into an old building), there were two switches (bath and sink) and two corresponding lights. That was obviously done back in the days when you did just put on the immersion prior to needing hot water.

 

[JohnW2]

If on single tariff, I'd agree - no point.

Glad you agree.

However, there's an argument that (from the manufacturing and distribution PoV) it's not worth doubling your SKU count to provide single immersion units for single tariff customers, and double immersion units for dual tariff customers.

True, but the fact that its better for manufacturers/distributors to only produce cylinders with provision for two immersions does not mean that anyone has to fit two ('blanking plugs' are cheaper than immersions!). Unless they come with factory-installed immersions (very rare, at least for vented ones), it's therefore those who install them, rather than the product, which results in installations with dual immersions.

For those using electric only heating and who have E7 like tariffs, then heating the whole tank off peak is the only sensible way to operate it. For those occasions when you "run out" of hot water, having the upper immersion makes sense to heat only the upper part of the cylinder.

As I keep saying/asking, is that really materially different from running the lower immertsion for a short period of time (e.g. with one of those 'boost' {'time lag'} switches)?

... who would have an electric-only cylinder if they had the option of other heat sources ?

Well, that depends upon what the 'other heat sources' are. I have the facility to heat my cylinders with LPG, but haven't done that for very many years since (although it's gradually creeping closer in price) heating water with E7 electricity is cheaper than heating it with LPG.

As will be apparent from the above, I continue to struggle to see the point/need for the upper immersion, even with E7 (or similar).

Kind Regards, John

 

[AndyPRK]

I thought E7 was going out of fashion.

I think my tank comes with 2’heaters in larger form and with heating coil from boiler

I’ll check the make in a minute.

 

[JohnW2]

I thought E7 was going out of fashion.

Well, it's becoming progressively less financially attractive - and, as has always been the case, is, in general, only usually worthwhile for people with storage heaters (not having storage heaters, I'm an exception which some might say 'proves that rule'!).

Of course, if EV charging ever takes off in a very big way, then the situation might reverse, with the 'cheap rate' of dual-rate tariffs (like E7) becoming the daytime, not night-time, hours!

I think my tank comes with 2’heaters in larger form and with heating coil from boiler

My tanks all have a coil and two immersions. However, as I've just written to Simon, I don't use the coils since cheap E7 electricity is still a cheaper option than LPG (although it is gradually 'catching up'!).

Kind Regards, John

 

[AndyPRK]

Made by jet

 

[JohnW2]

Made by jet

Fair enough, but what did you mean by "2 heaters in larger form"?

Kind Regards, John

 

[SimonH2]

... but the fact that its better for manufacturers/distributors to only produce cylinders with provision for two immersions does not mean that anyone has to fit two ('blanking plugs' are cheaper than immersions!).

Can't speak for vented cylinders, but from what I've seen it seems to be standard for thermal stores to come with the immersion(s) fitted.

 

[AndyPRK]

Fair enough, but what did you mean by "2 heaters in larger form"?

Kind Regards, John

Sorry. In larger capacity. Eg 200 litre plus from memory.

 

[JohnW2]

Can't speak for vented cylinders, but from what I've seen it seems to be standard for thermal stores to come with the immersion(s) fitted.

Yes, I believe that's true and, as I implied, I think also many/most unvented cylinders in general. However, I don't recall having seen a vented one which came with factory-fitted immersions.

In fact, there might be an issue in relation to the 'SKU count' matter you mentioned before. I live in an area of extremely hard water, and if I use 'standard' immersions, they only last 'five minutes' - I therefore have to use appreciably more expensive ones. If immersions were factory fitted, they'd either all have to be fitted with immersions much more expensive than those in soft water areas would need, or else the manufacturers would have to up their 'SKU count' and offer multiple options.

Kind Regards, John

 

[JohnW2]

Sorry. In larger capacity. Eg 200 litre plus from memory.

Thanks for clarifying. Mine are 140 litres and, as I said, have a coil and provision for two immersions.

Kind Regards, John