Are Condensing Boilers more efficient in real life?

hailsham

The big selling point of condensing boilers is that they are more efficient and will therefore save you money by reducing your gas consumption.

Has anyone, who has changed their boiler from non-condensing to condensing, done before and after comparisons, say over a couple of years, of their gas consumption (kWh)? If so what reduction in consumption did they achieve?

Cardew

Well you can only buy condensing boilers now(except under special conditions) so I suppose the question really comes down to "is it worth replacing an old non-condensing boiler with a new boiler?"

This has been discussed at length in this forum on several occasions.

Modern boilers have an efficiency of 90% or so. Although I read several article that dispute that those figures are achievable in practice in typical installations. I have no idea if those doubts have any substance.

If you look at the SEDBUK tables you will find few boilers have an efficiency below 60% - my 21 year old Ideal is 65%.

The Royal Institution of Chartered Surveyors stated recently :

The average cost of installing one of these modern boilers is £1,720, but saves on average just £95 off people's gas bills." See:

http://www.telegraph.co.uk/news/ukne...erts-warn.html

The other major consideration is that modern boilers are stuffed full of electronics and 10 years life seems to be the average life expectancy; where on the older boilers there is little to go wrong and plenty of people get 25 years or more.

So several of us on this forum have reached the conclusion that it doesn't make economic sense to replace a servicable but less efficient boiler.

david29dpo

I agree. I replaced my old gravity boiler with a combi condensing 6 months ago. Saving about £100 a year but i am on LPG. I constantly worry when it will go wrong.

hailsham

Cardew wrote: »

Well you can only buy condensing boilers now(except under special conditions) so I suppose the question really comes down to "is it worth replacing an old non-condensing boiler with a new boiler?"

This has been discussed at length in this forum on several occasions.

I know you have to buy condensing boiler (with special exceptions), Also, I wasn't trying to start a discussion on the merits of replacing an old but working boiler with a condensing, but find out if any one has done real-life comparisons of the before and after consumption

Modern boilers have an efficiency of 90% or so. Although I read several article that dispute that those figures are achievable in practice in typical installations. I have no idea if those doubts have any substance.

Again I agree that 90% may not be realisable on old installations as the radiators etc would not have been sized for a condensing boiler.

If you look at the SEDBUK tables you will find few boilers have an efficiency below 60% - my 21 year old Ideal is 65%.

But those are efficiency when new figures. A boiler which is 25 years old may now only be 50% efficient or even less.

Several of us on this forum have reached the conclusion that it doesn't make economic sense to replace a serviceable but less efficient boiler.

Couldn't agree more. A cost benefit analysis will show that you would be unlikely to recoup the capital outlay on a boiler before it needed replacing.

stevehead

Cardew wrote: »

Modern boilers have an efficiency of 90% or so. Although I read several article that dispute that those figures are achievable in practice in typical installations. I have no idea if those doubts have any substance.

Once the principles by which condensing boilers acheive their efficiencies are understood, then surely it's easy to see the circumstances that they won't work properly.
Basically, you have to be able to cool the flue gasses enough to cause condensation. The only way to do this is with the incoming water feed from your radiators. If you can't keep this water cool enough, then condensation will be incomplete or non existent.

There are condensing boilers and then there are fully modulating condensing boilers. Fully Modulating means that the rate of gas burn is highly variable. These will be efficient in a wider range of circumstances.

Pssst

I too would question the overall costs of running some modern boilers. As Cardew states,they cost a lot to buy and maintain and have a lower lifespan. In the end,it boils down to individual assessments. I am a great advocate of efficient storage systems in family type houses rather than combis.

My terraced house has a CF Spacesaver 50 boiler.It must be near 25 years old. I've just flushed out the system in november and added some inhibitor and Fernox F3. Its range rated and currently running at about 40,000Btu. Its on minimum setting and the house is lovely and warm with plenty of hot water in my well lagged fortic cylinder in the airing cupboard.. My last bill in october was £80 quarter for the boiler and cooking. I have a well insulated loft,cavity wall ins,and good quality DG upvc.

globalds

There is a thread on an alternative to gas CH here :
http://forums.moneysavingexpert.com/showthread.html?t=1310449

Cardew

hailsham wrote: »

But those are efficiency when new figures. A boiler which is 25 years old may now only be 50% efficient or even less.

.

On what grounds do you conclude that the efficiency will drop off?

That is a genuine question.

Have you seen any evidence to prove that point?

I have 2 non-condensing boilers - An Ideal Mexico and a Worcester combi in an annex

I have the full manual for each and the only adjustment that could in anyway affect their consumption is the size of the pilot light.

The full servicing schedule consists of cleaning and visual safety checks.

I have asked several Corgi fitters over the years, and they all state that there is nothing to affect the efficiency of the boiler.

If your contention is correct, then you surely must be able to back it up with evidence??

Pssst

Cardew wrote: »

On what grounds do you conclude that the efficiency will drop off?

That is a genuine question.

Have you seen any evidence to prove that point?

I have 2 non-condensing boilers - An Ideal Mexico and a Worcester combi in an annex

I have the full manual for each and the only adjustment that could in anyway affect their consumption is the size of the pilot light.

The full servicing schedule consists of cleaning and visual safety checks.

I have asked several Corgi fitters over the years, and they all state that there is nothing to affect the efficiency of the boiler.

If your contention is correct, then you surely must be able to back it up with evidence??

The only efficiency change that i can think might occur is how efficiently heat is transferred to water in the heat exchanger. this might decline slightly due to water quality,silt,scale or whatever but of course can always be rectified.

stevehead

Why is it that at any given time, when I amble past the multitude of condensing flues in my neighborhood some are pluming like a steam train, and others are making all the right noises but with invisible exhausts?

hailsham

I accept that parts can be replaced - provided they are available - which will bring the boiler back to original spec. But that is like saying: my 25 year old broom is as efficient as it was when I bought it - and I have only replaced 15 heads and 10 handles.

However, there does come a time when parts are no longer available, so the burner starts wearing, the heat exchanger get silted or corroded, thermostats go out of spec etc. The efficiency of the boiler drops and there is nothing you can do about it. It was this scenario I was thinking of when I said boiler efficiency could drop to 50%.

But, as I said in an earlier post and others have said in this and other topics, replacing a boiler before it is dead is not cost effective. Though that begs the question whether central heating in a house is ever cost effective!