Off peak storage heater charging duration

We’ll have to make some assumptions about your system, until you give us more details.

The normal arrangement is for the storage heaters to start charging at the beginning of the offpeak period, in your case at midnight. Unless you have further control over them, they will keep charging until they’re fully charged. Some more modern ones will limit the amount of charge they take according to what they expect to discharge the following day. Two hours may be enough. 

Do you have a hot water tank also being heated during offpeak periods? An immersion heater will typically draw just as much power as a storage heater. 

We’ll be able to offer better advice once you tell us exactly what equipment you have.

Firedog thank you for your reply.

I've got 1970s Dimplex storage heaters & no off peak immersion heater was on. My new tariff is OVO Economy 7 after the smart meter was fitted - hours defined as midnight - 7am.

After my new smart meter was fitted my off peak meter red light started blinking rapidly last night at 12.03am & stopped at approx. 3.50am. Thats 4 hours off peak instead of the 2 hours off peak before my smart meter was fitted - when I was on an Economy 7 off peak type tariff with a Radio Teleswitch.

That's double the off peak hours (just for the storage heaters) & cost.

I agreed to the smart meter because I was told the signal was being turned off at the end of June. I was given an installation appointment 48 hours later. 

The IHD hand held device works well.

I've read on the OVO Forum about asking the OVO support team to reconfigure the ECAUL/ALCS configurations via SMETS commands - is this relevant in my case ?

Thanks.

In the first instance, yes. We find that the ECAUL/ALCS reconfigure trick solves most of these cases so it’s worth a try. The worst it’ll do is just refresh with the exact same config as the meter already had, or fail to go through and do nothing.

Blastoise186 thank you.

Thank you.

OK, so the immersion heater is switched off. I wonder how you heat the water now? Or do you perhaps, like me, do away with using the hot water tank and boil up a kettle or two when you need some hot water? What about baths or showers?

AS the name implies. Economy 7 gives seven hours of power at a lower rate, specifically to allow for charging storage heaters and water heaters overnight. Any electricity you use between midnight and 07:00 will be billed at the lower rate, not just that used by the heaters. 

What controls do you have for the storage heaters? For example, some have dials on the top for ‘input’ and ‘output’, but there are many variations. It may be possible to achieve what you want by adjusting the available controls. 
  

Yes, it sounds as if that’s what it takes to charge up the heaters. If they don’t discharge fully during the day, they will take less charge the following night, but I don’t think that’s particularly likely - older heaters aren’t as good as modern ones at retaining the heat.
  

No. Your meter appears to be working just as intended: it starts recording offpeak usage at 00:03 and will do so until 07:03. The heating circuit which powers your storage and water heaters will be live for exactly the same period. 

Once we know what controls you have for your storage heaters, and how you heat water, we’ll be able to make more suggestions. It would help to know the make and model numbers of the heaters, and photos are always welcome.

Firedog - my immersion heater was not turned on during this off peak period. It is used earlier. My daily electricity use is the same.

The OVO electrician replaced my previous meters with a smart meter. That's the only change. Now my off peak meter (storage heaters charging only) is on from midnight - 4am approx instead of two 1 hour pre smart meter charging periods - increasing the bill.

The storage heaters heat input dial settings (for colder weather) have been left the same as pre smart meter so the installation of the smart meter - & its settings - is the only change made.

Its nothing I've done at this end so it must be the new smart meter & its internal settings controlled remotely by OVO.

Thank you, but I’m still a bit confused about the arrangement you have. 

• Where do you live? The first part of your postcode should be close enough for us to nail down the tariffs and timings of the various plans, both before and after your meter exchange.
• How do you pay for your electricity - Direct Debit, on receipt of bill or prepayment? This also influences which plans are or were available to you. 
• What was the name of the tariff you were on before the meter exchange? It should be given on a recent bill, e.g. THTC, Simpler Energy, Superdeal … there are many possibilities.

I would advise against asking for the ECAUL request to be sent, because there’s nothing to suggest that the load switch in your meter isn’t doing just what it’s supposed to: to make electricity available to power-hungry equipment like heaters during the night at a lower rate. 

You say “my immersion heater was not turned on during this off peak period. It is used earlier.” There is only one offpeak period each day - from midnight to 07:00 (+ 3 minutes). If you had the immersion heater switched on before midnight - perhaps using a boost function - it would have been using electricity at the peak rate, which may be much more expensive. 

You haven’t exactly told us what has changed, just that the change was caused by the new meter. You mention that the bill has increased - where do you see this? Are you comparing daily meter readings from before and after the meter exchange?

If your previous arrangement gave you enough heating from the storage heaters to be comfortable all day without supplementary heating*, then you should be able to limit the amount of charge the heaters take by screwing down the input dial. It sounds as if it’s the output setting that’s dictating how much charge they take, and this is demanding almost 4 hours of charge. Because the power to the heaters is no longer restricted to only two hours a day, they are taking whatever they think they need. The restriction made sure they couldn’t achieve this before, so it’s plain that you’ll have to vary their controls to match your requirements. 

Your old system depended on a radio signal to energize your heating equipment. That radio signal will not be broadcast after 30 June this year at the latest, so it’s time to adapt to the new arrangement. It’s unlikely that you will be much out of pocket as a result of the meter exchange. 

*  I’d be surprised to hear that this is in fact the case. My own experience of old night storage heaters is that while they might keep the temperature at a reasonable level until sometime in the afternoon, it’s all downhill after that. I have either to light the fire at sunset, or cocoon myself in an electric blanket to ward off hypothermia,  should I feel like watching television of an evening.

Firedog - thanks for your reply.

Postcode - TW5.

Payment on receipt of bill. 

Tariff before smart meter - Simpler Energy - Flex Rate 01 October 2024, & Simpler Energy - Flex Rate 01 January 2025 (copied from bill).

The smart meter was installed & OVO gave me a new tariff - Economy 7, hours defined as midnight - 7am.

Before my smart meter was installed my Off Peak meter red light blinked quickly from 10.30pm -11.30pm & also 4.30am - 5.30 am (total 2 hours) caused by my storage heaters being charged. No other Off Peak using equipment was on during that period.

I thought that my new smart meter would just send my meter readings automatically to OVO, that my new Economy 7 tariff times would be moved to 12am-7am, & that my storage heaters would continue to be charged for two 1 hour periods i.e. = same cost.

I don't understand why my smart meter is running off peak for 4 hours instead of 2 - doubling my nightly Off Peak cost.

One odd thing occurred last night.

Because my storage heaters were being charged for 4 hours instead of 2 hours they seemed hotter than before the smart meter. I turned down each storage heaters' heat input dial for safety's sake at 4am . The smart meter red light blinking began slowing down markedly & nearly ceased. My IHD unit then showed minimal electricity use.

I obviously can't wake up at 4am to manually reduce each storage heaters' heat input dial.

Before the smart meter was installed the storage heaters were charged up off peak for two 1 hour periods each night. Why 4 hours now ?

I want my storage heaters to be charged up for two hours each night to have the same cost.

I can’t be sure about any of this, but from what you say, before your smart meter was installed, you had electricity at offpeak rates to your storage heaters for two hours each day. You haven’t said when your water tank is heated, even though it could well be using as much energy as a storage heater. It could be that your immersion heater was also being powered at the offpeak rate. This could be a major element in your electricity bill.

On the old plan, you were paying 22.29 p/kWh for the offpeak rate for heating and 27.47 p/kWh for peak rate (anything other than heating). 

On your new Economy 7 plan, the offpeak rate is 19.56 p/kWh while the peak rate is 29.18 p/kWh. 

It is quite normal for customers with storage heaters to use the largest share of their energy on heating. If this is your situation, then the 12% saving in offpeak usage costs will outweigh the 6% higher peak usage cost. Only you know your usage pattern, so you will have to do your own sums to work out what the costs might now be.

Now, the two-hour/four-hour charging question. Your storage heaters have a certain capacity, which is usually designed to deliver an acceptable amount of heat during the day. What is acceptable depends on the size of the space being heated and the preferred temperature. How to achieve that temperature depends on the weather.

To give that desired amount of heat would normally involve charging the heaters for half the number of hours you want to maintain the temperature during the day. Seven hours of charge would give 14 hours of heating. You have clearly been making do with less, to keep costs down. I see that you still haven’t made any mention of supplementary heating, so it could be that the four hours or so of heating you were probably getting during the day was enough to keep you comfortable. Is that the case?

The input setting on the heaters dictates how much power the heater draws. The ‘cold weather’ setting is probably the highest, meaning that the heater will draw as much power as it can until it has reached its capacity. If the heater itself feels too hot after charging, you should try turning the input dial down to, say, its middle setting. You can see on the IHD the effect of doing this, because the kW being drawn should be less at a lower input setting. You’ll have to experiment to find the setting that works for you. There should be a thermostat in the heater that will prevent it from overheating.

If you have access to your online account, you should be able to see just how much the heaters are consuming every half-hour during the night. The IHD can also tell you how much electricity was used since midnight, say. 

I’m writing this to explain that it’s not just how many hours the heaters are charging for that counts, but also how quickly they’re charging. This also matters because the heaters are clearly not particularly well insulated (they wouldn’t ever feel ‘too hot’ if they were), so they are discharging some heat while they’re charging - during the night when you probably don’t need it. The longer you can make the charging part last, the longer the heater will be able to deliver heat the following day. 

Thank you for reply Firedog.

My immersion heater has no timer. It is manually turned on & I don't put it on after midnight so its electricity consumption wasn't on during my storage heaters 4 hours  charging.

I don't have any supplemental heating. My storage heaters are wide stand alone ones which are quite good. I have one wall mounted in the hall (bad electricity board shop advice) which is ineffective.

Explaining the p/kWh of my old/new tariffs was very useful. The lower Off Peak rate will help.

I've never had any timer control for my storage heaters. It was always two 1 hour off peak charging periods from their installation. I assume that the electricity board electrician set it up that way when he installed them or maybe the electricity company did that at their end ?

I understand your point that it is not only how long my storage heaters are being charged, it is also how quickly. The OVO smart meter electrician upgraded some of my meter cables to wider ones 😧 - perhaps that means that more current goes to my storage heaters ?

However I'm missing something.

I don't understand why a new smart meter with a new tariff with different Off Peak hours & pricing would cause my storage heaters to receive charging for 4 hours instead of the previous pre smart meter 2 hours.

Even with my new tariff 12% off peak reduction 4 hours charging will be more expensive than 2 hours. My IHD showed an off peak £2.25 approx hourly charge. 2 extra hours  = £4.50 x 30 days = £135 extra a month. OVO gains - but I have extra cost which wasn't mentioned by OVO on the phone when they discussed a new tariff for me.

That may not be particularly economical. Any usage between 07:00 and midnight will be billed at peak rate. A water tank could take 5-10 kWh to heat up from cold, depending on the temperature it’s heated to and how big the tank is. 10 kWh at peak rate costs you almost £3. If you were to switch the immersion heater on at midnight and off in the morning, it would cost less than £2. A reasonably well insulated tank should stay hot for at least a day. 

The short offpeak periods were part of your old Flex heating deal, which no longer applies. The schedule was set by the RTS, and managed by the electricity network operator (UK Power Networks). They have been replaced by one single offpeak overnight period. Your meter now switches power on to the heaters at midnight. If you want to restrict how much electricity they draw, turn down the input dial.

Please don’t rely on the £p figures from your IHD; they are only a guide, and the big numbers you see are instantaneous values. If you boil a kettle for tea, it will show something like £0.90 per hour. Because the kettle is only working for a couple of minutes, the cost of boiling it will be only something like 10p. Get used to looking at the kW figures in order to spot higher-than-normal consumption from time to time, e.g. when you turn the immersion heater on.

Your online account will tell you far more about your usage and what it’s costing than I can guess at.

Firedog - thank you for explaining about the old Flexi deal which no longer applies, as it was controlled by my Radio Teleswitch Service (RTS) which was removed with the new smart meter installation.

That explains why my previous x2 Off Peak charging periods are now only one period at the start of my Off Peak period - midnight.

What stops my Dimplex storage heaters drawing Off Peak current ? Is it a thermostat in each heater or unlikely the end of the Off Peak period at 7am ?

In addition, what is the schedule in the Auxiliary Load Control Switch (ALCS) ? You mentioned it in the attached post a year ago. You suggested to the OP that although their smart meter was switching from Peak - Off Peak - Peak at the correct times their ALCS schedule might not be right.

Thank you.

Both. The heaters are fed from a circuit separate from everything else (although I would normally expect the water heater to be on the same circuit).  This makes sure that heat storage equipment is never using power at the peak rate, because this ‘switched’ circuit is only live during offpeak hours.

If a heater reaches capacity or the maximum temperature set on its thermostat, it will stop drawing power even though the offpeak period hasn’t yet ended.

The normal arrangement is for the load control switch to close at the start of the offpeak period and open at the end of it. The example you saw was of a switch that wasn’t doing this, which is why I suggested the customer ask for it to be corrected. In that case, heaters were charging during peak periods, costing more than they should. As far as I can tell, your control switch is operating just as intended, so there’s no need for any change. 

I’ll say again, just in case you missed it: all electricity you use during the offpeak period will be billed at the offpeak rate, and all electricity you use in peak hours will be billed  at peak rate. It no longer makes any difference what the electricity is used for, as it may have done on your old plan. This is why it’s important to aim not to run any power-hungry equipment - like your immersion heater - during the day.  

Firedog - thank you.

Been on to OVO chat. There is an Economy 10 tariff with Off Peak times - 12am-5am, 1pm-4pm, & 8-10pm GMT.

It seems to be cheaper Peak/Off Peak/Standing Charge than my new Economy 7 tariff which is Off Peak midnight - 7am.

Would my storage heaters potentially charge up in each of the 3 Economy 10 Off Peak time periods ?

My situation with a new smart meter is somewhat confusing.

New Economy 7 tariff Off Peak - midnight - 7am.

Before smart meter I had a now redundant RTS controlled tariff which switched on my storage heaters for only 2 hrs a night - 10.30pm-11.30pm & 4.30am-5.30am. Now my smart meter charges up my storage heaters between midnight - 7am. From 2 hrs to up to 7 hrs. Will this increase the Off Peak element of my total bill ? (I appreciate that it is not just charging time but how much current is used as well).

In addition I now have to wait until midnight to manually turn on my immersion heater to get Off Peak rates instead of 10.30pm as before my new smart meter. It doesn't have a timer on it.

I see the need for a smart meter - but I thought that when getting a new smart meter I would have roughly the same bills & not have to turn on my immersion heater until after midnight.🤔🤔

That sounds unlikely. Where you live, the peak/offpeak unit rates for Economy 10 are currently 26.98/20.90 p/kWh, as opposed to 27.79/18.63 p/kWh for Economy 7.  Note that it’s significantly more expensive to pay on receipt of bill rather than by Direct Debit.
  

Yes, in just the same way as they now charge during the Economy 7 offpeak period. 

I did ask earlier, but is your immersion heater wired on the same circuit as the storage heaters? That would be the normal arrangement with any peak/offpeak arrangement, but it may have been different under the Flexiheat plan. 

Is there an indicator by the immersion heater switch to show when it’s heating up?

If it’s wired together with the storage heaters, it would have power during the same offpeak period. Depending on how big the tank is, and how well insulated, it may be enough to allow it to heat up fully one night; this could give enough hot water to last for two or three days. The thermostat will switch the power off when the tank has reached its target temperature. Again, you’d have to experiment. 
  

My immersion heater can be switched on at any time of day so it can't be on the Off Peak only circuit. Its electricity used in the Off Peak period presumably is charged at that rate even though it isn't on the Off Peak only storage heater circuit ?

It has a thermostat & it is possible to hear when it is no longer heating up.

The OVO chat lady mentioned an Economy 10 tariff (I had signed in so my having a smart meter should have shown up) but the OVO website stated that there is no Economy 10 smart meter. My smart meter would have to be replaced by a non smart Economy 10 meter & I would have to pay an installation charge.

If you have Economy 7/9/10, then ALL electricity usage during Off-Peak hours is tracked as Off-Peak and charged at the cheaper rate, regardless of what’s using juice.

Likewise, ALL usage at Peak times is charged at Peak rates. Please make sure to factor this into your usage patterns so you don’t accidentally rack up huge bills. If memory serves, OVO wouldn’t be able to reimburse/refund you nor offer a discount if you ended up using high power stuff at the wrong times.

Blastoise186 - thank you.

Yes, that’s how it works. It doesn’t matter how an appliance is wired up or what it’s for: if it’s used during offpeak hours, its usage will be billed at offpeak rates.

I suggest you try just one night switching the immersion heater on at five past midnight, and switching it off again the next morning. It will have heated up to its target temperature and switched itself off. Then note how long the hot water lasts for. 

I think you must have found an old article. OVO has been installing smart meters configured for Economy 10 for a long time. It’s not certain that it will be quick or easy to re-configure your present meter just now, though.

You were concerned that you were now getting seven offpeak hours instead of the two you were getting before. Economy 10 gives ten hours of offpeak power. What changed your mind?

A bit of a delay in replying…

When I requested a new smart meter I thought that there wouldn't be any other implications. 

Before the smart meter my Off Peak storage heater charging was restricted, by the electricity board on storage heaters first installation, to 10.30pm-11.30pm & 4.30am-5.30am - a total of only 2 hours.

With the smart meter the Off Peak storage heater charging period is now 12am-7am - up to 7 hours. Although it depends on how much current the storage heaters draw, up to 7 hours charging could put the Off Peak cost up a lot ?? ☹️

In the summer I will turn the heaters input dials down/off but next winter I'm concerned about the increased Off Peak cost.

Secondly, re. the Economy 10 tariff I was trying to align my Off Peak hours to my evening immersion heater use. I don't want to leave it on overnight, & rely on its thermostat to turn off, for hot water later that evening. My pre smart meter Off Peak hours started 10.30pm. I used to switch it at 10.30pm & it heated up by 11pm summer & 11.30pm winter.

My new Economy 7 tariff Off Peak hours start at 12am. Switching it on then means my immersion heater will heat up by 12.30am summer & 1am winter which is not as convenient.

A smart meter was necessary but it had led to other considerations.

Hey ​@Chas888 

I understand your frustration. We’ve had similar conversations with other community members on the forum before.
 

I’ve taken the below information from a similar topic. There is some variation but not much. 

When are my peak/off peak hours?

If you have a Smart meter installed by OVO, the off-peak times can be worked out using your Meter Point Administration Number (MPAN). You can find your MPAN on the ‘Plan’ page of your online account or OVO app (download for Android or iOS)

Please be advised that Secure, Aclara and Honeywell smart meters don't adjust for BST. The result of this is that during summer your off peak times will be an hour later than advised above. 
 

• Everything you need to know about an Economy 7 (Eco 7) energy plan F.A.Q.

• Getting a SMETS2 smart meter with storage heaters, underfloor heating or other 5th port appliances Tutorial

• Can you tell me my day/night switching times for Economy 7?

Emmanuelle_OVO - thanks for your reply.

I wasn't told on the phone by the OVO advisor that my new Aclara smart meter wouldn't adjust to BST so my new BST Off Peak hours won't be 12am-7am but will be 1am - 8am … 

I'm not switching on my immersion heater at 1am.

My old Off Peak hours started at 10.30pm, 11.30pm BST.

Secondly, that OVO advisor also probably wouldn't have known that my pre smart meter tariff was capped at 2 hours a night instead from 12am - 7am or 1am - 8am .... but OVO head office might have known - or asked me.

The change to a new smart meter shouldn't penalise a customer twice. I feel a bit aggrieved.

I think I need a new OVO tariff - or a different company. 👎

Easier solution is just to fit timers to your heaters. They’re fairly easy jobs for an electrician to do.

Likewise, if you only need to heat the water for two hours a night, then you can just set said timers for two hours a night.

Blastoise186 - thank you.

Installing new equipment shouldn't result in any downsides for a customer.

I don't think that it's helpful to change my Off Peak from 10.30pm to 1am.

Changing my 2 hour nightly cap for off peak storage heater charging to up to 7 hours is concerning for costs.