Yearly kWh for an average flat / immersion heater expense

Chrysalis

You could lower the target temp, or you could simply have it on less often, so its not on during the full eco 7 time period.

Ultimately there is a cost to wanting access to constant hot water.  Although I do understand why people would want to run immersions automatically at cheaper times of the day.

If there is no existing timing system, perhaps you could install one?  The idea was suggested to me I think in my own immersion thread.

Something like this.

https://www.amazon.co.uk/Timeguard-FST24-Timeswitch-Storage-Immersion/dp/B01E9R2SZO/

Scot_39

Wouldnt the thermostat be enough for many.  Unless runs a lot of hot water before end of e7 window, it probably won't re trigger within the 7 hr window for a modern of well jacketed tank.

My overnight is only 5 hrs and pretty sure it only heats once in that period.

The timer set for any shorter than thermostat would only mean the tank not getting to full set temp - which is already set low anyway (if c50C).

But could be used to say delay heating start to say 5 am rather than say midnight - meaning water hottest just before start to use and overnight tank losses reduced a little.

Chrysalis

Yep delaying the start would be the most effective way of using it. 
Thermostat throttle saves some power, but would still be a fair amount, after my thermostat got fixed, I would watch the live usage, to see when it would start throttling back and how long for, it was still coming on 3000w at a time for 5 min spells every 10-15 mins.

Scot_39

Sounds like too low a hysterisis.

Thought immersion thermostats  had a good few degrees deliberately to prevent that frequent switching behaviour - in past iirc as high as 8-10 C

bob2302

Chrysalis said:

You could lower the target temp

The OP said that it's already on its lowest setting.

Personally I'm very glad I don't have a tank. Someone quoted a figure of 2kWh/day for the losses from a well insulated tank. My electric shower averages 0.5kWh per shower.  

Scot_39

The manufactures of modern tanks like Gledhill do quote losses in that range - for instance Gledhill quote around 39-89W for one of their direct / indirect cylinder ranges - or c0.96 for smallest 120l - 2.1 kWh for 300l largest - per day equivalent - at 60C - and that's just the tank.  Others like Heatrea quote direct in kWh per day - in similar range on the one I checked it capped out at 1.6x kWh.

One of the reasons combi's are more favoured by those without a massive instantaneous hot flow demand - but tanks are still common in homes with 2 bathrooms / showers etc. as a combi might struggle.

And it's only really wasted heat in summer.

I quite like the "airing" cupboard heat my tank losses provide - it keeps any risk of dampness out of the linens - and I can always open the hall door if it's cold to heat the hall a little more (and of course probably increase the losses to a colder airing cupboard as a result)

But as my shower is cold fed - and I am an otherwise low hot water user - I do often wonder if a couple of undersink units might be the way to go - but then I'd lose the small "airing" cupboard.

Swipe

bob2302 said:

Chrysalis said:

You could lower the target temp

The OP said that it's already on its lowest setting.

Personally I'm very glad I don't have a tank. Someone quoted a figure of 2kWh/day for the losses from a well insulated tank. My electric shower averages 0.5kWh per shower.  

I'm very glad I have a tank and an electric shower which I try to use mostly during off peak. I only put the timed immersion heater on as and when required for a bath and in sub zero temperatures to protect the header tank in the loft. The kettle meets my hot water requirements for everything else, washing up etc.

Chrysalis

Scot_39 said:

Sounds like too low a hysterisis.

Thought immersion thermostats  had a good few degrees deliberately to prevent that frequent switching behaviour - in past iirc as high as 8-10 C

One of the advantages of having a smart meter, can see what is actually happening.  Not all immersions may behave the same as mine,l but I have no doubt if you running an immersion for an entire off peak period, the obvious way to save energy is to add a timer and only let it start much closer to the cutoff time.  Maintaining temperature still costs energy.

PJ2000

Thanks for all the comments - interesting to hear that the averages I've been looking at are generally not for our setup.
A few points just to answer a few of the questions:

We do not have a pumped shower. As one of the posters wrote above - we just have a pump that gets the hot water to the taps and shower - it also helps with toilet flush.

I have tried using the (VERY) old storage heater to give some heat and then add in heat later in the day when we're in the rooms - but it seems pointless - we generally aren't in during the day and the warmth doesn't last very long - the room temperature is generally as cold in the evening as it would've been if I hadn't put them on at all! I appreciate this doesn't say much for our insulation - which is something we are looking into...

Appreciate the comments about legionella and the tank - I have checked the water temperature previously - and (from memory) it seemed to tally with the dial and safety standards - thanks for reinforcing why the dial can't be turned down lower! i will check again though.

We do own - so we could change the system if necessary.

We would very much like to be off the economy 7 tariff as we don't think it's very worthwhile. Two similar flats in our block have recently stripped out the storage heaters and added simpler panel heaters which they can control through an app, as needed, for the evenings...

Thanks so much for all the advice!!

EssexHebridean

Have you thoroughly investigated the settings for the old heater to be sure that any heat-release delay is set and that sort of thing? Generally from my experience old Dimplex ones are relatively straightforward to work out, old Creda ones are a bit more "opaque" and take a bit more experimentation! (aka - guesswork!) 

Be very cautious about considering installing panel heaters - as they do tend to be one of the more expensive methods of heating!