Gas boiler efficiency

brook_heather

Spoonie_Turtle said:

Is it definitely 132,000kWh - is the meter in m³ and the bill thinking it's in ft³?

I have recently checked the meter readings and it is correct - the meter is m3 - it is actually the same Schlumberger model that I used to have.  The bill is based on actual meter readings so I don't think there is any issue with billing.

Until a year ago their gas bill was half this as they kept the unused rooms mostly unheated but they took in a Ukrainian familly last year and so more of the rooms are now heated.

There are a lot of large high ceilinged rooms with numerous single glazed windows, solid brick walls and probably limited insulation under floor and in the roof so yes a lot of heat will be escaping.  Most of the lounge windows have now been replaced with double glazed units but they have to be specially made custom windows due to the metal casement (not sure of the terminology) and so expensive.  Replacing the boilers will give the biggest saving I think and then they need to look at more insulation.

QrizB

brook_heather said:

I am currently looking into the high gas usage for my parents house which last year was 132,000kWh (yes I know this is excessive) ... They are currently on a very cheap 3-year fix at 2.5p/kWh which expires shortly so until now they have not wanted to pay for new boilers but their new price will be at the July 1st cap so much more expensive.

I imagine you have some the calculation yourself, but their current gas bill (on the cheap fix) is about £3500 a year.

On the July cap it will be more like £10000 a year.

brook_heather

QrizB said:

I imagine you have some the calculation yourself, but their current gas bill (on the cheap fix) is about £3500 a year.

On the July cap it will be more like £10000 a year.

Yes something like that and with a new boiler possibly under £8000.  Slight complication is that the house is currently on a commercial contract and it needs to be moved to a residential contract so at least it will be at the capped rates - the out of contract commercial rates are much more and a new 3 year fix well above the July cap.

BUFF

FreeBear said:

BUFF said:

FreeBear said:

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

& if it was e.g. 65% new you can pretty much bet that it  won't be that now 30+ years later.
If they do go ahead & replace then they will have to not only also update the controls but the system must run at 55C flow temp or below - this may also require changing/replacing old radiators as their output will drop at the lower flow temp. Tbh modern radiators will be more efficient/lower water capacity anyway than 30+ year old ones.
It's probably worth considering a complete system redesign/renewal (or selling the house & downsizing). 

Yes, new controls will be required, as will TRVs on most (all?) radiators. But I'm not sure the flow temp of 55°C is correct.

It is, one of the Section 5 of Part L changes that came in - max. 55C flow temp (for heat pumps 45C).

FreeBear

BUFF said:

FreeBear said:

BUFF said:

FreeBear said:

That 89% figure looks like just the burner efficiency rather than how much energy is being transferred to the water within the CH system. You'd be better off referring to the manufacturer's data on overall efficiency. If they say 65%, then it would certainly be worth fitting a new condensing boiler. With the cost going from 2.5p/KWh to 10p/KWh, the payback time would be fairly short, especially if the parents are getting through 132,000KWh per year.

& if it was e.g. 65% new you can pretty much bet that it  won't be that now 30+ years later.
If they do go ahead & replace then they will have to not only also update the controls but the system must run at 55C flow temp or below - this may also require changing/replacing old radiators as their output will drop at the lower flow temp. Tbh modern radiators will be more efficient/lower water capacity anyway than 30+ year old ones.
It's probably worth considering a complete system redesign/renewal (or selling the house & downsizing). 

Yes, new controls will be required, as will TRVs on most (all?) radiators. But I'm not sure the flow temp of 55°C is correct.

It is, one of the Section 5 of Part L changes that came in - max. 55C flow temp (for heat pumps 45C).

5.10 Where a wet heating system is either:

a. newly installed

b. fully replaced in an existing building, including the heating appliance, emitters and associated pipework

all parts of the system including pipework and emitters should be sized to allow the space heating system to operate effectively and in a manner that meets the heating needs of the dwelling, at a maximum flow temperature of 55°C or lower.

Where it is not feasible to install a space heating system that can operate at this temperature (e.g. where there is insufficient space for larger radiators, or the existing distribution system is provided with higher temperature heat from a low carbon district heat network), the space heating system should be designed to the lowest design temperature possible that will still meet the heating needs of the dwelling.

The way I read the above is if a completely new heating system is being installed (boiler, rads and pipes), then it should be designed with a flow temperature of 55°C in mind. It does not say that the flow temp must be 55°C or lower. In fact, the following paragraph says that a higher temperature can be used. In either case, it doesn't stop the end user from turning the dial up on the boiler.

Still. A useful nugget of information for when my new boiler gets installed. So thanks for pointing it out.