Boiler Efficiency vs Reliability

ffs

My parents have a gas boiler made by Ideal that was installed nearly forty years ago. Obviously it is much less efficient than the condensing boilers that are now available. I would really like to advise them to install a new boiler, but I can't bring myself to do so because the Ideal boiler has never gone wrong, and the only maintenance it ever requires is changing the £2 thermocouple every few years. The separate Grundfloss pump still works perfectly as does the separate timer. The diverter valve has only just started to leak slightly but even that is manageable. I have had several boilers fitted to houses in the last twenty years, and they have all suffered serious and expensive failures. Most recently a Ferroli required a new set of controller boards costing nearly as much as the boiler itself. Although insurance and or maintenance contracts are available, that still adds significantly to the running cost, and they have exclusions and limits on the age of the boiler, so within a few years of fitting a new boiler it could become hideously expensive to repair or replace.
So while I'd like to recommend a new fuel efficient boiler, I can't bring myself to do so. Are there any boilers made today that could last just 20 years without any parts failures let alone 40?

Cardew

I also have an Ideal boiler which at a mere 20 years old is still in its prime if your parent's boiler is anything to go by!!

There have been several threads on the merits/demerits of replacing older inefficient boilers with modern condensing boilers. I posted this a couple of days ago in this thread:

http://forums.moneysavingexpert.com/showthread.html?t=1127697
I

don't know if you have read this article about a report from Royal Institution of Chartered Surveyors:

http://www.telegraph.co.uk/news/ukne...erts-warn.html
About boilers they state:

"Installing a condensing boiler – frequently cited as one of the best ways to improve the energy efficiency of a home – can take 18 years to make a pay back.
The average cost of installing one of these modern boilers is £1,720, but saves on average just £95 off people's gas bills."

I would disagree with their economics!

If someone invested £1,720 it would produce at least £95 in interest. If the boiler lasts 10 years and needs to be renewed, it makes no sense to me to replace a boiler.

There is an interesting link provided by 'Mech' that indicates 15 years might be a reasonable life now for boilers.

Whilst I am a heavy user of gas, I also can't convince myself that 'upgrading' from a 65% efficient Ideal boiler makes economic sense.

amtrakuk

I would keep the old boiler going. I have also had a boiler gone US after 7 years.

As the saying goes "They don't build them like they used to".

gmatwork

!!!!!! wrote: »

So while I'd like to recommend a new fuel efficient boiler, I can't bring myself to do so. Are there any boilers made today that could last just 20 years without any parts failures let alone 40?

It's not even quite that simple a dilemma. Many old systems are not suitable for modern condensing boilers, which need low water content, fully pumped systems to work, so it can mean a lot more expense than just a boiler change.

Having said that, if you do change, go for a good quality replacement. I'd suggest Vaillant or Worceter (one of the models that has been around for a few years so they've ironed out any weaknesses) and it should enjoy a long trouble free life.

Theo_Cupier

The actual operating efficiency of an older boiler will not be as high as the initial manufacturer claims (eg 65% as Cardew suggests, above).

As the heat exchange becomes furred up, its efficiency will drop quite dramatically.

The issue in making a direct comparison with modern condensing boilers is this:
- old boilers have wide gauge pipes in their heat exchange, which can labour on for ages, gradually declining in efficiency but fundamentally still working
- new, condensing boilers have far finer pipes in their heat exchangers which mean than when they fur up they just stop working.

This obviously has an impact on the economics dynamic of the comparison - one which I, frankly am not man enough to quantify!

Cardew

Theo_Cupier wrote: »

The actual operating efficiency of an older boiler will not be as high as the initial manufacturer claims (eg 65% as Cardew suggests, above).

As the heat exchange becomes furred up, its efficiency will drop quite dramatically.

That is an interesting comment and I would be interested to see any data to support that contention.

Subjectively that is what I suspected might happen, as the efficiency of most things(and people!!) deteriorates with age.

I have asked this question of several Corgi fitters and even rung the manufacturers and they do not agree that there will be any noticeable drop in efficiency.

I have also posed the question on MSE and nobody has come up with the same conclusion as you.

Indeed some have posted that they have carefully monitored their consumption and there has been no noticeable increase in consumption over many years.

Indeed in the 20 years I have owned this boiler I have also monitored my consumption each year(and recorded figures) and, whilst I readily concede that is hardly a controlled experiment, I have certainly not noticed any increase in consumption, let alone a "dramatic" increase.

Whilst I am no plumber I would not have thought the heat exchanger being 'furred up' would affect thermal efficiency. In the same way as a clogged up radiator would not dissipate heat as well, but merely act as a smaller capacity radiator and again not affect thermal efficiency.

So how are you using the term efficiency?

The definition that counts is that a boiler of 65% efficiency will use 10 kWh to produce 6.5 kWh of useful heat.

Do you have any evidence e.g. reports/data to support your statement or is that a subjective opinion? In particular how is that drop in efficiency measured.

Nicholas

You would also need to factor in how much higher energy bills are going to jump, and for that we would need a crystal ball:(

mech_2

Unless you're talking about a combi boiler, limescale shouldn't be an issue. The heating tends to be a sealed system these days. Even in an open vented system I can't see evaporation from the header tank causing significant new water to enter the system.

If we're talking about corrosion products ("sludge"), then the rate of flow through the boiler is too great for it to settle there. It will settle in the radiators though, whatever kind of boiler you have. There's an interesting paper here: http://www.sentinel-solutions.net/en/downloads/technical-information-sheets/general/Technical-Paper-Independent-Boiler-Efficiency-Study.pdf that concludes loss in boiler efficiency due to severe sludge in the system is in the order of 3%.

I can see limescale being a good argument against combi boilers, both condensing and non-condensing, but it does depend where you live. If you get limescale in your kettle it might be best to avoid a combi boiler. Where I live the water is exceptionally soft. No limescale anywhere.

Part L building regulations now require that with water hardness levels above 200ppm, a scale prevention device must be fitted to all new and refurbished hot water boilers.

Theo_Cupier

You make an interesting response, Cardew.

My initial thought was that by "efficiency" I meant the number of KWh (in gas burned) required to heat a defined volume of water from X degrees Celcius to Y degrees Celcius.

My gut reaction is that calcium carbonate (limescale) has a far worse thermal co-efficient than copper. In other words, relatively speaking, it acts as an insulator in the boiler's heating coils in the heat exchange between the source of heat and the water being heated.

Wikipedia lists the thermal conductivity of copper as around 380. That of limestone (Calcium carbonate, same basic chemical as limescale) is 1.5.

To my understanding, this means that copper is about 250x more efficient in conducting heat than limescale.

Hence, even a uniform 1mm layer of limescale along the length of the pipes would be the equivalent of adding 250mm of copper between the heat and the water.

However, limescale does not deposit evenly and the cracks and troughs in its formation can lead to other problems such as hotspots and - of course - bottlenecks in the pipe leading to problems with water circulation.

Now, I have no figures to hand (yet) which directly show the demonstrable decrease in efficiency of a boiler which might arise from this, but experienced heating engineers I've spoken to have suggested that the efficiency of furred up old boilers can drop to well below 40%.

Cardew

Theo_Cupier wrote: »

You make an interesting response, Cardew.

My initial thought was that by "efficiency" I meant the number of KWh (in gas burned) required to heat a defined volume of water from X degrees Celcius to Y degrees Celcius.

My gut reaction is that calcium carbonate (limescale) has a far worse thermal co-efficient than copper. In other words, relatively speaking, it acts as an insulator in the boiler's heating coils in the heat exchange between the source of heat and the water being heated.

Wikipedia lists the thermal conductivity of copper as around 380. That of limestone (Calcium carbonate, same basic chemical as limescale) is 1.5.

To my understanding, this means that copper is about 250x more efficient in conducting heat than limescale.

Hence, even a uniform 1mm layer of limescale along the length of the pipes would be the equivalent of adding 250mm of copper between the heat and the water.

However, limescale does not deposit evenly and the cracks and troughs in its formation can lead to other problems such as hotspots and - of course - bottlenecks in the pipe leading to problems with water circulation.

Now, I have no figures to hand (yet) which directly show the demonstrable decrease in efficiency of a boiler which might arise from this, but experienced heating engineers I've spoken to have suggested that the efficiency of furred up old boilers can drop to well below 40%.

I am an Electrical Engineer so this is not my game.

However I don't see the relevance of limescale to thermal efficiency.

This is more Mech's field of expertise from what I gather from his contributions.

I can see that blockage of pipes, boiler and radiator might reduce the output of the CH system.(is that what your heating engineers mean?) Therefore a CH system when new might be capable of producing 100,000 Btu/h but only 50,000 Btu/h when old.

However using the figures above, if it only uses 50% of the gas to produce the latter figure, that is very different from efficiency in terms of running costs.

amtrakuk

mech wrote: »

Unless you're talking about a combi boiler, limescale shouldn't be an issue. The heating tends to be a sealed system these days. Even in an open vented system I can't see evaporation from the header tank causing significant new water to enter the system.

If we're talking about corrosion products ("sludge"), then the rate of flow through the boiler is too great for it to settle there. It will settle in the radiators though, whatever kind of boiler you have. There's an interesting paper here: http://www.sentinel-solutions.net/en/downloads/technical-information-sheets/general/Technical-Paper-Independent-Boiler-Efficiency-Study.pdf that concludes loss in boiler efficiency due to severe sludge in the system is in the order of 3%.

I can see limescale being a good argument against combi boilers, both condensing and non-condensing, but it does depend where you live. If you get limescale in your kettle it might be best to avoid a combi boiler. Where I live the water is exceptionally soft. No limescale anywhere.

Part L building regulations now require that with water hardness levels above 200ppm, a scale prevention device must be fitted to all new and refurbished hot water boilers.

The Homecare engineer said the heat exchanger had "sludged up". From what I could work out he said the reason the boiler was cutting out was after turning off the hot water the heat exchanger and sludge was super heated causing the boiler to cut out. He suggested before I wanted to draw hot water, turning the central heating on so there will be a constant flow through the heat exchanger.

Where did the sludge come from? Occasionally I used to top the central heating circuit.

I live in Leeds and can't really say I have got hard water, I do get red stains wound the plug hole.