Cheapest way to run immersion heater

Section62

wittynamegoeshere said:

I need one of those black curly wigs so I can say "ey ey calm down".

You've lost me.  Are you suggesting wearing a wig alters the efficiency of water heaters?  I'm fairly sure that isn't how it works.

wittynamegoeshere said:

I do understand how electrical heat works, no need to describe the basics.  Both turn electricity into heat, one does it at the time you need it, on demand.  The other does it whether you need it or not, just in case, then leaves it sitting around going cold.  Which do you think is likely to be the most efficient and why?

As I've said several times, it depends on the circumstances in which the heater is being used.  You've been over focussing on the loss of heat from a hot water cylinder, based on your unrepresentative experience.  There are lots of other factors that need to be taken into account to work out which heating method is most efficient overall in a particular situation.

wittynamegoeshere said:

Tell me what I've missed.  Does the heater somehow put the electricity into tiny rockets and fire them into space?  Otherwise it's dificult to imagine how it could mysteriously make energy vanish somewhere so could use more power than an immersion heater.

With that I'm not sure whether you actually want a serious discussion about the relative efficiency of different methods of water heating? I'm assuming not.

wittynamegoeshere said:

I'm accepting as an assumption that anyone deciding what system to get will do their own research before going ahead and won't do this solely on the advice of a random stranger on the interweb.  But hopefully they'll consider all the options and not just start from where they think they should start.

That's the crux.  And if I may remind you, at the start you said "The cheapest way to run an immersion heater is to not have one at all!  Get rid of the stupid tank altogether and get something like this..."

Considering all the options should mean just that, considering all the options.  Not randomly deciding that hot water cylinders are "stupid" and "a thing of the past" and excluding them from consideration.

You've actually contradicted your opening assertion by pointing out that a hot water cylinder and instantaneous water heater can be used in combination.  The "tank" can't be "stupid" if it can be used to make instantaneous water heating more efficient and cheaper... think about it.

k_man

@wittynamegoeshere

@Section62 has a point, it is inconsistent to state:

An open mind is a good place to start.

When part of your opening statements included:

The cheapest way to run an immersion heater is to not have one at all! Get rid of the stupid tank altogether and get something like this...


Maybe just a poor choice of words.

Section62

k_man said:

@wittynamegoeshere

@Section62 has a point, it is inconsistent to state:

An open mind is a good place to start.

When part of your opening statements included:

The cheapest way to run an immersion heater is to not have one at all! Get rid of the stupid tank altogether and get something like this...


Maybe just a poor choice of words.

That really was my point from start to finish.  I'm not saying instantaneous heaters are 'bad', just that like any other method of heating they have positives and negatives.

If you are considering one yourself it is important to be aware they aren't intended as a direct replacement for a hot water cylinder or combi boiler.  Even the 9.6kW model is described as only being suitable "For light handwashing at up to 2 basins or light dish washing at a single basin".  (I'm not entirely sure what light dishwashing means)

The standard output temperature is only 38C (adjustable), and they are primarily intended for use with spray taps.  The manufacturer states they aren't suitable for use with thermostatic mixing valves or taps, or to supply a single lever mixer tap.

Also note that they should be installed as close as possible to the point the water is being used. (e.g. under the kitchen sink) Not necessarily where the existing hot water cylinder is.

We installed/used similar units in site welfare facilites and also in our public conveniences.  They worked well enough and for those sort of niche requirements I'd probably still recommend one.  But as a replacement for a domestic hot water cylinder, matching the household requirements to the capacity of the heater(s) is essential.  And probably accepting a fair amount of compromise.

wittynamegoeshere

Apologies if I've ruffled any delicate feathers.  But I stand by my previous assertion, that an on-demand heater is definitely, always more efficient than a hot water cylinder heated by an immersion element.  There really aren't the whole heap of complications that are alleged to be involved.

I don't know how much more simply I can possibly explain it, but I'll have another attempt.  Energy is always conserved, it doesn't just vanish.  Electricity goes into the heater, hot water comes out.  It doesn't have any high-powered floodlights, massive loudspeakers or somehow make the energy vanish into space.  I'm being ridiculous, mainly because this debate is pretty tedious.

If I try and explain further I'd only be repeating myself and/or angering the MSE gods further.

Stepping away from the nit-picking and selective quoting to find apparent contradictions like some kind of daytime TV series barrister, and getting back to actual facts, it's a very efficient way of heating water IF compared like-for-like against using an immersion heater on single-rate electricity.

Of course if there are other factors such as cheap rate electricity, a heat pump, solar panels etc etc then it becomes a more complicated judgement.

I'm not judging it via google, I have one installed.  It's plumbed into an absolutely standard basin tap, not a spray.  It also feeds a mixer shower.  It looks, feels and behaves exactly like any other hot water system but costs much less to run.  Nobody, on washing their hands or having a shower, would know there was anything unusual about it.

I've already stated that it does have limitations but, having tried one in our second bathroom as a cautious test, I'm now happy to install a second that will feed the main bathroom and kitchen.  Ignoring all other factors, it would be preferable if a torrent of high-speed steaming water came out of the tap instead of the modest but acceptable flow of warm water you get with one of these.  But, for a difference of what I know will be £100s per year, I'm very happy with this compromise, and would recommend that others might want to think about one too.

But I'm not saying chuck away your cylinder now, and I credit others with the intelligence to not do this based on one random stranger's recommendation.  What I did beforehand was to fill a 5L bucket from a tap using a stopwatch to see for myself the sort of whatever litres per minute flow rate you get looks like.  You can also get a thermometer and mix hot and cold water to find out what 40 degree water is like, basically it's what you'd call "warm".  I'd say 45 would be more like warm-to-hot.

All I can say is that it's definitely adequate, but only just.  But it also definitely, certainly saves lots of money compared to what I had before.

wittynamegoeshere

A further point...  I did state that steaming hot water would be preferable.  But this would only be the case in the kitchen, and only then sometimes.  Hot water is not desirable for hand-washing and can be hazardous.  You can end up jiggling a mixer valve to not scald you.  It's not a good idea to set a cylinder to heat to only a warm temperature, as the breeding bugs would create a health hazard.  So hot water is mostly hotter than actually needed to keep it clean.  In commercial settings, concealed mixer valves are often used to mix the hot with cold so that warm water is supplied to the tap - you'll often see the metal lump under the sink in public toilets that does this.

A far as I know, this is only a factor with a tank, as the water is essentially stagnant, sitting there doing nothing.  When you're heating the flowing water this is not a factor, as it gets completely flushed out every time.  Perhaps someone with experience of regulations can confirm, but I believe that this is the only situation where warm water is OK.

I do know that heat pumps also heat the tank to only a warm temperature, but the systems also use an immersion element to give it a weekly kill-off.  So this is an additional cost, presumably this leads to the water temperature being unpredictable too.

[Deleted User]

I agree that this debate is getting tedious and rather repetitive. It really is up to each homeowner/consumer to look carefully at their own consumption/costs. As I have said before, a well insulated Greenstar 250L unvented cylinder works just fine for us with the cylinder temperature set to 65C.

So far today, one shower; one bath and washing up the breakfast and lunch dishes has used 1.88kWh of electricity. The immersion heater is agnostic when it comes to the source of the electricity.

wittynamegoeshere

How do you work out that 1.88kWh?  That sounds very low, unless the hamster had that bath.  I just can't see how you could fill a bath alone for that amount of energy. Guesstimated figures here suggest 5kWh for a bath...

https://www.withouthotair.com/c7/page_50.shtml

Your cylinder is probably very well insulated but is about £800 plus fitting.  It's extremely unlikely that the average cylinder in the typical flat that may have been built some time ago by a penny-pinching builder will be of a similar standard.

Anyone would need to get together some proper figures on heat loss to compare their old one and its heat loss against the super duper one, to find out how soon they're likely to get back that £1000+ fitted cost.  I'd start by analysing lots of numbers to see what makes sense.  I suspect that many wouldn't, most people don't replace things until they break.

But all I'm saying is to consider all options, I really don't understand what people are getting emotional about.  Personally I'm very happy with a less capable system that definitely costs less to run.  We will definitely not be having a bath with our system, it would go cold as fast as it filled.  But the system we did have was ridiculously expensive to run.

doodling

Hi,

wittynamegoeshere said:

[...]
Personally I'm very happy with a less capable system that definitely costs less to run.  We will definitely not be having a bath with our system, it would go cold as fast as it filled.  But the system we did have was ridiculously expensive to run.

At the risk of being accused of selective quoting, your assertion that the instantaneous heater is always more efficient isn't true then?

Whilst this is MSE and therefore money is an important focus, ultimately people like to live how they want.  Telling people who might enjoy baths that they should use an instantaneous heater when you yourself admit that it would be less efficient is not MSE.

Instantaneous heating has its place but in the case of instantaneous electric heating, that place is something of a niche for a reason. I have never found an electric shower which delivers a flow which I find acceptable but I know that other people have other views.

Only by understanding the exact circumstances and therefore the whole question can an accurate answer be given. Blind assertions that a particular approach is stupid are not helpful.

[Deleted User]

wittynamegoeshere said:

How do you work out that 1.88kWh?  That sounds very low, unless the hamster had that bath.  I just can't see how you could fill a bath alone for that amount of energy. Guesstimated figures here suggest 5kWh for a bath...

https://www.withouthotair.com/c7/page_50.shtml

Your cylinder is probably very well insulated but is about £800 plus fitting.  It's extremely unlikely that the average cylinder in the typical flat that may have been built some time ago by a penny-pinching builder will be of a similar standard.

Anyone would need to get together some proper figures on heat loss to compare their old one and its heat loss against the super duper one, to find out how soon they're likely to get back that £1000+ fitted cost.  I'd start by analysing lots of numbers to see what makes sense.  I suspect that many wouldn't, most people don't replace things until they break.

But all I'm saying is to consider all options, I really don't understand what people are getting emotional about.  Personally I'm very happy with a less capable system that definitely costs less to run.  We will definitely not be having a bath with our system, it would go cold as fast as it filled.  But the system we did have was ridiculously expensive to run.

No calculations needed. The HARVI energy clamps do all the work.

Mstty

Do you have an ASHP @[Deleted User] I can't remember who does and who doesn't on here lol

The figures don't add up for the use you have had out of the tank.