Posted By: Carol hunterIt's just that we're getting stiffer and older

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Posted By: Carol hunterThinking Mass/storage heater type of electric back up just for background warmth when/if we're away or when we can't light fires any more.

Sounds like a night storage heater.
They can still be had - but IMO unless you have night rate or off peak or PV generated electricity there is no advantage of these over an ordinary electric heater. Both have an efficiency (COP) of 1:1 at the point of use.

If you have a timed cheap rate or PV generated electricity then a storage heater might make sense (heat now / when the sun shines and delay usage by about 6 hours).

Otherwise without cheap rate electricity what about a small A2A heat pump (that can also give cooling in the summer if needed) which should give a COP of 3:1 or better. Depending upon your view of ROI a COP of more than 3:1 may prove better than a storage heater but difficult to beat a simple fan heater or electric oil filled radiator (on wheels) especially if portability is useful.

BTW electric storage heaters that I have seen needed a dedicated 16A supply (more for larger ones). Would this cause a problem for your supply?

Posted By: Peter_in_Hungary[Storage heaters} have an efficiency (COP) of 1:1 at the point of use

In terms of kW of heat delivered = kW of electricity used, yes. But in terms of heat that's useful, no. They pump heat out all night, when you prob don't need it, an effect moderated with varying success by mechanical means of impeding the convective component of their output, but on the whole, significant heat wasted.

Posted By: djhstorage heaters that use water to store the heat?

Water has half or less the volumetric specific heat of the special solid blocks used, as well as the blocks get a lot hotter than 100C. So prob over 3x more volume, if water.

Yes, can be gd, just saying it's not quite like the 100% of an instantaneous heater. A super-heavy house will even out peaks and make closer to 100% useful use of xs heat input at unwanted times. But for example no hope of accommodating someone's preference for sleeping with no heating, even window open!

BTW, original question, is clay a good medium for off-peak storage?

Posted By: fostertomIn terms of kW of heat delivered = kW of electricity used, yes. But in terms of heat that's useful, no. They pump heat out all night

Is that true even with modern (HHR) storage heaters?

It can be quite convenient having a deducated E7 supply in some ways. The timer appears to be imnune to power cuts, so you don't have to reset it after every little power flicker or cutlet. That's the major drawback to most electronic timers, at least where we live. They don't seem to have any memory of their previous settings, and don't simply restart when the power comes back on but require the ON button pressing again.

But if you have an old-fashioned E7 system then ALL electricity used during the E7 period is at the cheaper rate, so any old timer will access it. We used to just run our old washing machine and dishwasher by plugging them into a spur from the E7 circuit. Modern machines have to be reset every use using only their internal timers, not just by turning the power on.
But a storage heater can be charged through a plug-in timer on an ordinary socket, up to its current rating.


We used to have an antiquated E7 meter that used an actual mechanical clock for it's timer, electrically rewound. It slowly lost time over the years, so when we inherited it we got electricity at the E7 rate during the daytime.

I agree the modern trend for built-in electronic controls is bad. We regularly get power cuts and have to adjust everything after each one. It rapidly becomes annoying.

Storage heaters now require two mains supplies - a 24-hour one, and an E7 one :(

Just to chime in, on the subject of storing thermal energy in something other than water, there is also the SunAmp heat battery approach which uses Sodium Acetate as the storage medium. This is more 'energy dense' than water, so it can store more heat in a smaller area.

Not a direct replacement for a storage heater (more like a boiler/water cylinder substitute) but you can use them with an E7 tariff - we charge ours overnight, and I think they can be plumbed into the space heating system.

I have a lot of clients in a similar position, with the conumdrum of where to go for automated heating to back-up logs, or replace direct electric panel heaters. The go-to was always storage heaters, and I have provided these for various clients, with a lot of success (improved comfort and reduced elect consumption).

I now am going to the A2A solution more regularly for various reasons. Considerations that crop up are:

- storage heaters are expensive items at around £600-£800 each

- if you haven't insulated reasonably well, there will be a larger number of the storage heaters, and so the power draw will be very large (the charge rate is much higher than the release rate). That can lead to insufficient capacity on a standard single phase domestic supply (explains partly why they were often on their own phase supply with separate breakers etc)

- ASHP A2W appear to be hugely inflated in terms of the supply installation costs (my belief is installers take advantage of the gov't grants). Disruption for wet rads install is significant, and costs of copper, radiators, labour are huge. (I also include these for some clients, so not poopooing them).

- ASHP A2A can be had for a fraction of the price, are zero VAT rated like wet ASHP's, have a different supply/install market (more of a commercial refrigerant/aircon focus) and so aren't overweight with grant binging.

- disruption with A2A installation is relatively low

- A2A does not allow for storage of energy of course, so harder to take advantage of low rate tariffs, however ASHP is 1/4 running cost of panel heater on daytime. Storage heater would be a bit above 1/2 of that same cost. Ao A2A would be less than 1/2 of running cost of storage heaters.

- as noted above re. current capacity of your domestic single phase feed, if you go for octopus (which I have, and love it 100%), your car charger will take say 7kW power, which reduces the scope further for storage heater capacity (remember charge rate is higher than rated output).

- warm air from storage heaters is a bit closer (sensation wise) to the warm air from A2A, so it's not such a leap to having warm air, versus say UFH.

- A2A not being storage, does have the benefit of being more reactive, and lower risk of charging over night for a day that suddenly is 15oC warmer than the previous day (something not that uncommon these days). Storage heaters are pretty good at retaining heat, but not for 24-48 hours.

There is no one right answer for all. Every case has to be thought about carefully. The OP did ask for a heating solution, but as pointed out by others, it may be that including batteries in the mix might turn A2A into total winners, as they effectively become storage heaters, that are super responsive, but with a very low relative power draw, overcoming many of the issues raised above.

I have approached ASHP supply/install companies and had ridiculously high prices offered, compared with aircon companies, who are much more competitive. Caveat emptor.

A great 'Guide To ...'