Economy 7 or Single Rate?

Ildhund

GasAttacK77 said:

... based on the current tariffs available I'd have to get to about 60% night usage to see a financial benefit.

I haven't studied all of the posts in this thread, but this statement seems to me to be just plain wrong. There is no way that an Economy 7 tariff would be more expensive than its companion single-rate unless offpeak usage were 60% or more of the total. Ofgem expects price-capped E7 rates to be cheaper than single-rate if offpeak usage is at least 42%. The rates I've checked recently have all come up with savings so long as offpeak usage exceeds ~30% of total usage. I can only assume that this 60% figure arises from comparing apples to goats.  

There is a simple rule of thumb: take the night (offpeak) rate n and subtract it from the day (peak) rate d. Save the result. Now subtract the corresponding single-rate s from the day rate d. Divide the smaller number (d - s) by the bigger one (d - n). The resulting figure multiplied by 100 gives  an approximation to the 'break-even' percentage of offpeak use of the total above which E7 will be cheaper and below which more expensive. This little sum assumes that any difference in standing charge is insignificant. 
  

---

Here's an example, using Octopus' rates for the EMEB region:
  

32.84 - 26.37 = 6.47

32.84 - 14.64 = 18.2

6.47/18.2 = 0.3555

or ~36%. 

Scot_39

They are not that old if RF series.

But the 070RF is one of the smaller models - 2nd in 5 sizes -  that only takes around 1.56kW power when charging - so 10.9 kWh charge on a full 7 hrs charge.  With a 700W nominal output.

That's not a lot to heat a large room - like a typical living room to 21C in the coldest of weather.  The Dimplex site sizing tool iirc uses a -3C outside temp (recommends -5 for Scotland) - to size and defaults to 21C for living rooms and 18C for others from memory.

So for instance taking just the top 2 resellers from a Google search forvquantum rf series - this vendor states upto 5m2 based on 21C 

https://www.electricpoint.com/heating/electric-heating/dimplex-quantum-storage-heaters.html

And this one upto 7m2.

https://www.heatershop.co.uk/storage-heaters/dimplex-quantum-rf-hhr-storage-heaters-6

So roughly 2x3m - c6.5 x 10 ft.

As a guide - The UK minimum recommended for a single bedroom is c6.5-7.5m2 from a quick google.

My old living room nsh heater - has over double the charge power c3.65kW - and can charge with that on my e10 upto 10 hrs a day split overnight mid afternoon and evening (so hours in between to cool to create "space" for new charge) if needed in theory.

Depending on room sizes, walls, windows etc and location your heaters may well be underpowered for the coldest of days.  Even if coping on most typical uk winter days as far warmer than that sizing consideration.. But may have beenresorting to using the c0.5 kW boost element if not taking enough charge overnight to maintain 21C in coldest periods. 

Scot_39

Ildhund said:

GasAttacK77 said:

... based on the current tariffs available I'd have to get to about 60% night usage to see a financial benefit.

I haven't studied all of the posts in this thread, but this statement seems to me to be just plain wrong. There is no way that an Economy 7 tariff would be more expensive than its companion single-rate unless offpeak usage were 60% or more of the total. Ofgem expects price-capped E7 rates to be cheaper than single-rate if offpeak usage is at least 42%. The rates I've checked recently have all come up with savings so long as offpeak usage exceeds ~30% of total usage. I can only assume that this 60% figure arises from comparing apples to goats.  

There is a simple rule of thumb: take the night (offpeak) rate n and subtract it from the day (peak) rate d. Save the result. Now subtract the corresponding single-rate s from the day rate d. Divide the smaller number (d - s) by the bigger one (d - n). The resulting figure multiplied by 100 gives  an approximation to the 'break-even' percentage of offpeak use of the total above which E7 will be cheaper and below which more expensive. This little sum assumes that any difference in standing charge is insignificant. 
  

---

Here's an example, using Octopus' rates for the EMEB region:
  

32.84 - 26.37 = 6.47

32.84 - 14.64 = 18.2

6.47/18.2 = 0.3555

or ~36%. 

The OPs not using anything close to standard svt but heavily discounted single rates - at least one fixed 12m  - but sub 20p/kWh  c18.4 or 18.7p flat vat / ex vat ?.  So c7p cheaper than svt..

GasAttacK77

Scot_39 said:

They are not that old if RF series.

But the 070RF is one of the smaller models - 2nd in 5 sizes -  that only takes around 1.56kW power when charging - so 10.9 kWh charge on a full 7 hrs charge.  With a 700W nominal output.

That's not a lot to heat a large room - like a typical living room to 21C in the coldest of weather.  The Dimplex site sizing tool iirc uses a -3C outside temp (recommends -5 for Scotland) - to size and defaults to 21C for living rooms and 18C for others from memory.

So for instance taking just the top 2 resellers from a Google search forvquantum rf series - this vendor states upto 5m2 based on 21C 

https://www.electricpoint.com/heating/electric-heating/dimplex-quantum-storage-heaters.html

And this one upto 7m2.

https://www.heatershop.co.uk/storage-heaters/dimplex-quantum-rf-hhr-storage-heaters-6

So roughly 2x3m - c6.5 x 10 ft.

As a guide - The UK minimum recommended for a single bedroom is c6.5-7.5m2 from a quick google.

My old living room nsh heater - has over double the charge power c3.65kW - and can charge with that on my e10 upto 10 hrs a day split overnight mid afternoon and evening (so hours in between to cool to create "space" for new charge) if needed in theory.

Depending on room sizes, walls, windows etc and location your heaters may well be underpowered for the coldest of days.  Even if coping on most typical uk winter days as far warmer than that sizing consideration.. But may have beenresorting to using the c0.5 kW boost element if not taking enough charge overnight to maintain 21C in coldest periods. 

Sorry, the model I listed was for the upstairs Quantum. It's on the landing and was the only one that would fit the space.

The two quantums downstairs are about double the size, model QM125RF.

Maybe that explains why the upstairs heater has to use the fan more often because it's a smaller heater trying to heat a fairly large space.

FrugaiMacDugal

Get a proper electrician, who knows how Quantum works, to suss out your setup and give a quote for required upgrade.

If you intend staying long time, just get job done, and relax knowing you've got things sorted.

If it means a bit of upheaval, so what, do it now, you'll be cosy next winter and cheaper.

Scot_39

The 125 is much beefier - can take 2.76 kW for upto 7 hrs on E7 - nearly 20 kWh - and suitable for 12m2 on the second site listed above - in harsh winter - more in typical winter weather for large parts in UK.

So between the 3 you have potentially 50kWh at of peak - or in reality far far more at cheaper on ave single rate and either boost or extending charge windows - if you switch to one of those 18-19p deals - to heat the house.

I have gone over 40kWh during real extremes - and defintely not gotten near to 21 - by that I mean sub zero day and night plus windy - including leaving loft hatch open as have cold tank and pipes up there - that have frozen in the past without doing so - and despite far better lagging now - a few £s more in energy for normally only a few days - is much better than the alternative.  

GasAttacK77

Scot_39 said:

The 125 is much beefier - can take 2.76 kW for upto 7 hrs on E7 - nearly 20 kWh - and suitable for 12m2 on the second site listed above - in harsh winter - more in typical winter weather for large parts in UK.

So between the 3 you have potentially 50kWh at of peak - or in reality far far more at cheaper on ave single rate and either boost or extending charge windows - if you switch to one of those 18-19p deals - to heat the house.

I have gone over 40kWh during real extremes - and defintely not gotten near to 21 - by that I mean sub zero day and night plus windy - including leaving loft hatch open as have cold tank and pipes up there - that have frozen in the past without doing so - and despite far better lagging now - a few £s more in energy for normally only a few days - is much better than the alternative.  

Sorry Scot, I don't quite follow what you're saying there. Are you suggesting E7 should be the way to go, or the 18.65p/kWh SR?

Scot_39

No.

Just correcting the earlier comment re the 10kWh per heater being tight.

Even Ive probably hit 30 kWh

And pointing out on SR you could potentially get even more if need be - without using any other heaters (plug in heaters etc) - if really needed it.

If I plug say the lower R quote rate I think you said that you have found on the cheap single rate deals - so lets say 18.65p cheapest on the fix you are quoting for the two deals - into @ldhund equations

32.84 - 26.37 = 6.47    becomes 32.84 - 18.65 = 14.19

32.84 - 14.64 = 18.2

6.47/18.2 = 0.3555      becomes 14.19/18.2 = 0.78 = 78%

You estimated above you might get to 60:40 - so ....

But I wouldn't want to influence you overly.

Especially where fixing comes into play - thats a personal decision.

RedFraggle

One other thing to bear in mind, quantums don't work well if another heat source is used in the same room as they're constantly assessing room temperature to "decide" how much energy to store. 
If a panel heater is is keeping an area warm then the quantum will think it's summer. 

GasAttacK77

Fraggle - We have 4 panel heaters but the 2 that are in the same room / area as a Quantum aren't usually used.

Scott - I've tried that calculation using the very best SR and very best E7 tariffs I can find. The result was 58%. I think I could probably get close to that figure but is it worth it when the SR will end up costing roughly the same and I don't have to worry about what time things are used? Probably not.

My current plan is to go with OFTM SR at 18.65p/kWh but check their best E7 tariffs in October to see if it's worth switching. They've told me there is no charge to switch between different FR tariffs.