How long do storage heaters take to charge?

glocal

I am on E7 and the other day I had the lounge storage heater (Heatstore HSXC24N) on charging for 5 rather than the usual 7 hours. To my surprise, the following day we couldn't tell the difference. I am now wondering how many hours it actually takes for the heater to charge. Reducing that to 5, 3 or 2 hours could save significant amounts of energy and extend the life of the element. I am guessing there is a thermostat switching supply on and off, so it's not really 7 hours it consumes energy, but if, say, 2 hours is sufficient, it will still make a difference. I could and probably will experiment, but what do others do? Temperature in the lounge dropping in the middle of the night is not an issue here, so re-charging can start at 5am or so.

CashStrapped

It is all determined by the input setting. The higher the input the more electricity it will use and the more heat it will store. Unless the manual gives you kwh ratings for each input level then it is a process of working it out yourself based on night rate meter readings.

You will probably not notice huge difference in the actual temperature of the heat being released. It is more to do with how much it has to release.

I would not worry about extending the life of the elements. Storage heaters will go on for 20+ years without any maintenance.

Just ensure you use the controls as intended. Setting the input each night based on tomorrows weather. Leave the output on the lowest setting at all times and only turning it up for short bursts to release more heat (if required). The output should always be at the lowest setting during the night.

The storage heaters should be in charge mode during e7 hours only (anywhere from 12 - 6am). Why do you think yours only start charging at 5am?

Also ensure your E7 hot water tank is taking advantage of heating at night too, while being well insulated to retain the heat for the next day.

glocal

I have input and output permanently set to 1. The heater is very hot in the morning, so I don't see how it can store more heat. It then slowly gets lukewarm in the evening, so I don't think there is any spare heat to release. I notice that on average charging consumes 14kW more at night rate, which seems about right (7 hours x 2.5kWh). If charging can be done in 2-3 hours with the same results, I am wondering if I should reduce charging time. Intuitively, I don't see why any bricks will take 7 hours of extreme baking to absorb sufficient heat. That is unless it's really 7 hours of on and off charging regulated by a thermostat, in which case there is less (but not zero) wasted energy.

CashStrapped

The input may control how many elements activate. With the lower input levels, less elements may come on and only heat smaller portions of the bricks. The bricks then have less stored heat for the next day.

There will probably be some thermostat control involved. Again, this may be determined by the input settings.

Both these things will determine how much heat is available to be released, and what you individually feel is required as an input level. The background temperature also has an effect as to whether they will make it through the next day with enough heat. If you are still using 1 for the input level in current weather, then you must have a well insulated flat.

The bricks are very a dense material. They are designed to be heated for a intensely for a 7 hour period and then loose that heat very slowly. If you think about it, they are only heated for 7 hours but have to retain that heat and release it slowly for the next 17 hours.

- Are you saying you have tested the heater at the highest input and lowest input and see no difference in kwh usage?

DigForVictory

As the helper involved in relocating a storage heater, those things are *solid*. You really do not need to worry about the element - delicate fuse wire it is not, and the bricks are good solid lumps that leave you wondering if your back will recover in days, months or ever.

If the heater is warm enough after 5 hours, it will cool faster than if it had 7 hours, but thermal comfort is a matter of taste. By all means experiment, but if 5 hours is sufficient, let it stay at 5.

glocal

I never had to change the input setting, and seeing that set to 1 results in 14kWh overnight consumption, I am reluctant to change that to 6. The flat is indeed well insulated, but it may be something to do with people always telling me I don't a have a sense of cold That last point makes me less ideal for subjective tests, but I will experiment with different charging times and see what my gf thinks. If I find anything interesting I will report back, but somehow I doubt it.

CashStrapped

Out of interest, how are you manually restricting the charging time?

Due to the high power/load nature of storage heaters they usually are wired into fused spurs for safety rather than having a socket with the ability to put a timer on.

I would experiment with the input settings. You do not have to go straight to 6. Maybe turn it up to 3. You should still see a difference in recorded kwh use.

Do the storage heaters have any type of automatic function that may override manual input control?

If you discover that there is no difference in kwh use at any input level, this could indicate a faulty input control or thermostat. It may turn out it is currently using an equivalent input level of 6 (full power) regardless of what you have set it at.

molerat

That particular heater has a capacity of 24kWh with an input rating of 3.4kWh. To fully charge it from cold will therefore take 7 hours. The input switch will control the amount of charge put into the bricks so setting to 1 and using 14 kWh suggests it is only actually charging for 4 hours, leaving it switched on for 4 or 7 hours will make no difference (in reality there will be a small one) to the amount of electricity drawn, it is being governed by the input dial.

glocal

Good point! 14kWh sounds like full power. Each heater has a switch on the wall. This one actually has two -- the second one is for the boost function (and there is a boost button on the heater itself). Heaters are indeed fused separately in the fuse box, and there is also a digital timer I can switch on/off or program. So, there are several control points. The timer is probably there because my E7 gives me 2+5 hours with 2 hours gap, so some user control may be necessary. AFAIK, there is no automatic control other than a possible thermostat.

glocal

molerat wrote: »

it is only actually charging for 4 hours, leaving it switched on for 4 or 7 hours will make no difference

This would explain why I don't see a difference between 5 and 7 hours. Do you mean it works at full power for 4 hours and then stops, rather than trickle-charge for 7 hours? How does it 'know' when to stop? I am presuming there is no internal timer. Would that be a thermostat then?

molerat

The charging is either flat out on or off. There is an internal thermostat, that is what the input control is, which measures the temperature of the core and switches on and off accordingly. http://www.storageheater.co.uk/heatstore/hsxc12n-hsxda24n/hsxc24n/input-thermostat-cutout.html