Discuss CH upgrade - unreasonable gas usage expectations? in the Central Heating Forum area at PlumbersForums.net

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Hi all.

I recently upgraded our CH system, but rather than the expected drop in gas consumption, Octopus is saying we're using roughly 30% more! The installer has said they can downrate the boiler, but to my mind that addresses maximum consumption, not any inefficiencies there may be relating to the install itself.

In nutshell, the system has gone from a 20yr+ Baxi back-boiler (15kW), no TRVs, and 13 rads producing ~25k BTU; to a Greenstar 8000 Life (30kW), TRVs throughout, and 12 rads producing ~43k BTU.

I know that a 15kW boiler running at full tilt will consume less gas than a 30kW boiler, and whilst the rads are all more efficient, they are also larger (most went from single to P+). But I thought the increased efficiencies (a condensing combi that modulates, better rads, TRVs) would offset that. Did I have unreasonable expectations? I'd really appreciate some advice from more experienced heads!

Not sure if it's relevant, but worth noting that it takes an hour to raise the room temps by 2 degrees (to 18). It's an old house though - 1930s, 4 bed detached, EPC E - so I'd expect poor performance in that regard.
 
I’m guessing combi boiler ?
 
Are you comparing against last year this last period as it was also warmer are the kWh the same ?
 
Are you comparing against last year this last period
It's been tricky, but I have tried to find dates with similar weather when making comparisons. In the case of the difference I mentioned, we saw a 30% increase in m^3 used from 1st-10th Jan (old system) vs 12-21st Jan (new system). The latter does include a cold snap, but also some above average temps too.

are the kWh the same ?
No, and that's the crux of my concern; what I thought would be a more efficient system seems to be using more gas.
 
Not sure if this is helpful at all (appreciate it's not hard data) but this does show the trend pretty well:
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Don't forget your HW use, a combi going at full chat for a few showers/baths a day may well use alot more gas than a cylinder that needs partially recharging.
 
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Don't forget your HW use, a combi going at full chat for a few showers/baths a day may well use alot more gas than a cylinder that needs partially recharging.
We've experimented with not showering (!) and having showers at times where it obviously shows up on the usage charts and worst case, it looks like shower usage only accounts for about 0.6m^3 a day. The old system burnt through 0.48m^3 a day just idling, so I think HW is having a minimal effect on the difference
 
Do you have a smart meter?

My bills seem to go up every month despite me trying to cut back usage!!

I hope you figure out your issue soon.
 
Smart meters will be the new ppi claims in a few years.
Only if you let them fit one.

There's a program on tonight re "Smart" Meters Channel 5 20.00hrs.

The Boss of Octopus says "Smart" meters are already 10 years out of date and 3 million fitted "Smart" meters are not in Smart mode and need replacing / repairing.

That's with only around 60% of Domestic / Small businesses fitted with them. (late 2023)
 
Only if you let them fit one.

There's a program on tonight re "Smart" Meters Channel 5 20.00hrs.

The Boss of Octopus says "Smart" meters are already 10 years out of date and 3 million fitted "Smart" meters are not in Smart mode and need replacing / repairing.

That's with only around 60% of Domestic / Small businesses fitted with them. (late 2023)
Had one about 4 years, stopped working after about 18 months, still waiting on a new one.
 
What do you have to do read the meter manually and call it in?

Had mine about two years and it has been working great so far tbf, installer knew his business.
 
In case some data for comparison helps, I live in Devon, my gas consumption is about 90% heating 10% DHW. For December 2023 I used 262m^3 of gas and in Jan 2024 I've used 363^m3. I check my 'dumb' meter on the last day of each month, so the number of days contributing is 31 in both.
 
Agreed, they are very different systems. But surely any comparison would put the newer combi ahead in terms of efficiency?
Yes, boiler alone difference will be 15-20% at a guess. However, you have a lot more output to heating and a combi which runs full knacker while you run a tap, bath, shower etc.

I know the figures show the differences in boiler performance but there are always other things to take into account.
 

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