Inconsistency in gas consumed and charged for.

FreeBear

Dolor said:

records the actual burn time

How relevant is that when modern boilers modulate? A 24kW boiler which has modulated down to 6kW is clearly not using as much gas as it was at 24kW.  (For some daft reason, my WB 24kW boiler has a maximum output of 25.3kW).

Clearly, the only accurate indicator is the volume of gas as recorded by the meter which is displayed on the IHD (with up to 30 mins lag, or that obtained via a smart meter data pull.

I believe the WB also has a register recording the level of modulation. But you are right, neither will give an accurate consumption figure. And for most people, the data will be of zero interest.

Just a shame we have to jump through hoops to access the smart meter data via Bright (or similar) if we want to add the figures to a graph. Even then the gas readings will only be in 30 minute intervals.

John8S

Can I thank all those who have taken the time to reply to my post? I'm afraid that much of it has gone right over my head - though I do get the gist of much of it but to reply individually to each post would reveal just how little I do understand, and be far too simplistic.
However even if we leave the Hive out of the equation the fact is that the IHD tells me that x KWh have been consumed, and the fact that Octopus tells me that the cost of each is 10.33 pence I thought that there should be a logical correlation between the 2. So one day's number of KWh used should be comparable (directly with another day's. But apparently not - and if that's the case, as a reasonably average member of the public (I think!!) there's no point in many of us even trying to understand what these things are for! So as in most other areas of life we're just expected to live the proverbial mushroom life - i.e. live in the dark and be grateful for the um...waste we're fed on!n
Just to complete the infomation, the boiler is a condensing one - a Vaillant "ecoTec plus 832" set to preheat  for 7am. and goes off at 10.30 pm. The water for heating is set to 55 degrees and the hot water 'on demand' is set to 60 degrees.
The thermostat is set to 19.5 degrees (which is a bit too cool for me at my age - and level of softness! 71) and the Hive shows the temperature over the period has never gone below 18.2 degrees - even in the night ....so far. It is a big house with high ceilings and 11 radiators.
It just seems rather too ridiculously expensive to top up from a not so low starting temperature. Outside night temperatures have been about 6/7/8 degrees.We do have pretty decent cavity wall and loft insulation. 
Octopus's forecast of some £5k does seem a bit over the top - and it definitely won't be reached as I'll turn the damned thing off and freeze before I give in to that kind of madness! 
Anyway, thanks again to everyone who was kind enough to respond and apologies for not being clued up enough to take full advantage of the explanations/comments.

BUFF

John8S said:
 the IHD tells me that x KWh have been consumed, and the fact that Octopus tells me that the cost of each is 10.33 pence I thought that there should be a logical correlation between the 2.

So one day's number of KWh used should be comparable (directly with another day's. 

There is a direct correlation between the 2 & total cost of gas consumed. X kWh x 10.33p= total cost of gas consumed

This is where your supposition fails. This would be true only if they were directly comparable days i.e. same weather & same pattern of use. That does not happen in the real world. 
Even if your boiler runs for the same length of time on 2 different days it may be at varying power levels according to weather & use so uses a different amount of gas.

bagand96

John8S said:

However even if we leave the Hive out of the equation the fact is that the IHD tells me that x KWh have been consumed, and the fact that Octopus tells me that the cost of each is 10.33 pence I thought that there should be a logical correlation between the 2. So one day's number of KWh used should be comparable (directly with another day's. But apparently not - and if that's the case, as a reasonably average member of the public (I think!!) there's no point in many of us even trying to understand what these things are for! 

There is a direct correlation between the amount of gas you are using in kWh and the cost in pounds in your table. The days you use more kWh the more you pay (rough calculation showing around 10.8p/kWh which is very near your 10.33p plus VAT at 5%). 

What there isn’t a direct correlation to is the time your heating is on and the energy (kWh) used.  Gas isn’t “on” or “off”. It’s not the case that if your Hive heating is set to “on” then the boiler burns gas at a constant rate. It will vary day to day how much energy is required to bring the house up to temperature, and then how often the boiler needs to fire to maintain that temperature - this is the “modulation” people are talking about. There will be times when the heating is on but the boiler won’t burn any gas at all because the house is at temperature. Therefore the amount of gas used is variable. 

k_man

John8S said:

....
However even if we leave the Hive out of the equation the fact is that the IHD tells me that x KWh have been consumed, and the fact that Octopus tells me that the cost of each is 10.33 pence I thought that there should be a logical correlation between the 2. So one day's number of KWh used should be comparable (directly with another day's. But apparently not

As the replies above, there is a direct correlation between gas used, and charges per day, once you include the standing charge (which I work out to be about 27p per day based on your numbers).

Can you give an example of your daily figures where this doesn't work out?

[Deleted User]

As indicated in previous posts, the meter records usage in volume. When billing, the supplier converts this volume to kWh using an agreed industry formula based on the average calorific value of the gas supplied during the billing period TRUNCATED to 1 decimal point.

IHDs and third-party apps that use the smart meter data - PULLED directly from the gas meter - nearly get it right. Nearly - in the sense that they use a fixed calorific value (in the gas proxy meter and the various apps): that said, the difference in kWh will be small.

Provided that the supplier has sent the correct tariff to the GSME (the gas meter) then the cost calculations should always be the same. That said, my gas proxy meter hasn’t added the daily standing charge to my daily cost data for the past 3 1/2 years.

This is my usage for yesterday. My boiler is 24kW and my set temperature is 19C. The boiler flow temperature is 55C.

It is frequently said on this forum that my boiler must be condensing as I can see a large plume emanating from the flue. Wrong: at worst, a properly condensing boiler should just be emitting a few wisps of steam.