Expected energy saving from boiler change?

carstairs

Hi all,

Is there a calculator somewhere that will let me estimate my savings on gas bills from changing my boiler?

Currently have an old Worcester Bosch from 15 years ago, planning to get a new Baxi Main one. Both are small combi boilers for a small terraced house.

Apparently boilers that are 10+ years old are about 30% less efficient than when they were new, and also I’m guessing a new boiler now is more efficient than a new one 15 years ago!

Cheers

dogshome

Sure, a present day gas boiler will be more efficient than a 15 year old one, but I suspect that the gain is much less than 30% - Where did this figure come from and even if it's reality, how many years will it take for the gas use saving to recompense you for the £1200+ cost of installing a new boiler?

15 year old boilers were built to entirely different specifications, (Like tanks?), and if it me whilst spare are still available I'd hang on to it 

[Deleted User]

The problem with retro fitting a condensing boiler is that installers rarely carry out any heating calculations. They are also swayed by the homeowner’s wish for rapid HW heating. This leads to a situation where the new boiler rarely condenses. To condense there needs to be at least a 20C differential in the flow and return temperatures, and the latter must be less than 56C. For comfort, lower boiler temperatures need bigger radiators: that is, more radiator surface area.

To complicate matters further, fitting a boiler that is bigger than needed will result in a boiler that is forever cycling. Most modern boilers have a modulation ratio of 4/5: 1. This means that a 24kW boiler may only modulate down to 8kWs. 8kWs may be too much for a house that is up to temperature so the boiler cycles.

In sum, the new boiler may not be as efficient as you have been led to believe.

tim_p

We had a Gloworm boiler replaced after 30+ years of service a couple of years ago. Can’t say we’ve seen any measurable savings despite taking very regular meter readings. Pretty sure it’s like dogshome says, basically if it ain’t broke don’t fix it. Our new boiler cost around £1600 as part of a kitchen renovation and I know I’ll never see the savings (if any) pay back any of that. 

matelodave

As said above, you probably wont see a great deal of difference unless you have extra controls fitted and you use them wisely.

You could probably save nearly as much by fitting a programmable thermostat, TRV's and using less hot water - dont run it down the sink and use cold water where possible for rinsing stuff. Combi's are least efficient when used for short run-off, like washing your hands

A 15 year old boiler thats still working will probably cost you a lot less to run and keep running than buying a shiny new one despite being a bit less efficient. 

You can do some really rough sums without using a calculator or anything really clever. I'll assume that your gas bill is £600 a year, if a new boiler is 10% more efficient then you could save £60.

Even if it was 30% more efficient (which is doubtful) then you might save around £150-£180 a year. If a new boiler costs you £1500 then you could be in profit in ten years time (assuming that it's not broken down in that time or repairs are covered under a ten year warranty). Dont forget you'll have to cost in an annual service to maintain the warranty.

BUFF

It will depend upon what you have fitted, what you replace it with & whether that helps you to make any changes to your use.
Is your existing boiler a condensing boiler? If it is, then assuming a straight swop with no other changes, then you are probably looking at ~10% improvement rather than 30% imo.

13 years ago I had an old balanced flue boiler replaced with a fan-flued condensing combi (which I do run with low flow/return temps) & updated programmer+roomstat. Overall, I reckon that the savings over 13 years have basically paid for the boiler+installation but I also suspect that the controls probably account for a big chunk of the saving.
The next boiler replacement has no chance of paying for itself from efficiency improvements.

[Deleted User]

Worth a read. When you see a plume of steam coming out of a flue, the boiler isn’t condensing:

https://www.theheatinghub.co.uk/why-our-condensing-boilers-do-not-condense

carstairs

Thanks for the replies. Sorry I should have clarified, the old boiler has packed in with no hope of a fix. I meant we are planning to choose the Baxi as our new one, rather than another model.

carstairs

I just hope we’ll save a bit on the gas bill to offset some of the capital cost.

QrizB

I have a Worcester Bosch Greenstar 18Ri that is around 16 years old (it was about a year old when we moved in, in 2006).

When new it had an efficiency of 88.8%. It may have lost some efficiency since then but there's not a lot of scope for a new boiler to improve on the original; the current equivalent 18Ri ERP+ has an efficiency of 88.9%.

0.1% of my gas bill would be around 40p per year.

dogshome

OK, so your present W/Bosch is dead so it's a decision on what boiler to install.

Went through this process 4 years ago when Gas came to our village and I scrapped our ancient Oil boiler for the savings in running costs.

Did the research and decided W/Bosch would be best, but local plumber pushed Baxi, (Probably got some sort of kick-back), and pointed out that to get a 10 year warranty from W/Bosch you had to go through a series of hoops, ie, everything had to be Bosch including the remote controls, fit Honeywell or any other proven brand and no guarantee, plus the top of range Baxi was £100's cheaper than the comparetive Bosch.

Four years in and the Baxi has been faultless.

It gets it's mandatory annual service each year which costs £70, ( This price is fixed for 10 years), and Baxi sent out a reminder card each year when it's due.

I can't emphasis enough that you get a LOCAL INSTALLER - The "I - know - where - you - live" card  is worth gold dust