Heat only boiler

Cardew

DUTR wrote: »

I just found this

Will an efficient new boiler save you money?

, the Energy Saving Trust estimates the average saving per household on energy bills after installing a new boiler to be £300. This does not take into account how much installing a new boiler will cost.
The table below illustrates just how much a modern condensing boiler could cut your gas bills by, depending on the size of your house (a boiler that's 15 years old or more is classed as 'old' in these calculations. A lightweight boiler can be attached to a wall; a heavyweight boiler is floor standing.)
Annual fuel costs with different boiler types (source: Sedbuk)Boiler typeEfficiencyFlatBungalowTerracedSemi-detachedDetachedOld gas heavy weight55%£875£1109£1150£1288£1773Old gas light weight65%£759£957£991£1108£1519New non-condensing78%£652£817£846£943£1286New condensing89%£587£731£756£842£1142

These figures are based on a gas unit price of just 4.49 pence per kW (Sept 2011), and a standing charge of £30 per quarter.


So it looks like my boiler is classed as an old lightweight, so at 18.5kwh input and 11.5kwh is near the 65%


So still at the rates shown,it would take a good 7 years+ to repay itself, shall stick as I am :cool:

For some reason the EST always seem to exagerate savings in this field.

Also that there is very little to go wrong with the old type boiler, but plenty to go wrong with the modern condensing boilers that are stuffed full of electronics and it seems that 10 years is a reasonable life expectancy.

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 average gas customer uses 16,500kWh pa.(that includes those cooking with gas) This at 4p/kWh will cost £660 pa. before discounts for dual fuel, payment by DD etc

So if the EST's estimate of average saving per houshold is £300 'Based on a saving of 25% gas usage'. the figures simply don't add up.

Even many 30+ year old boilers according to SEDBUK have an efficiency of 65%.

diywhynot

Good explanation of condensing boiler technology here.

Ben84

Cardew wrote: »

Even many 30+ year old boilers according to SEDBUK have an efficiency of 65%.

I don't trust those ratings so much any more. I looked up mine and noticed that everything seemed to be 65% efficient, which raised suspicions. I eventually found my answer. Anything with a standing pilot light gets 65% stuck on it.

For actual figures, your boiler manual should contain details on heat input and output which you can do the maths with. The installation does affect efficiency too, positively or negatively, so it's not a definitive answer to how well your system is using fuel, but it's a better answer than the SEDBUK ratings.

Ben84

diywhynot wrote: »

Good explanation of condensing boiler technology here.

Page 19 answers my question. It's kind of obvious now. The more air allowed to mix with the fumes, the less saturated and less likely to condense the water vapor is.

DUTR

Ben84 wrote: »

I don't trust those ratings so much any more. I looked up mine and noticed that everything seemed to be 65% efficient, which raised suspicions. I eventually found my answer. Anything with a standing pilot light gets 65% stuck on it.

For actual figures, your boiler manual should contain details on heat input and output which you can do the maths with. The installation does affect efficiency too, positively or negatively, so it's not a definitive answer to how well your system is using fuel, but it's a better answer than the SEDBUK ratings.

Just re-checked mine
16.6kwh i/p and 11.7kwh o/p
the replacement 12 HE is 13.3kwh i/p and 12kwh o/p 'suggesting the same heat o/p for less i/p?
Or the solo 15 HE 16.9kwh i/p for 15.2kwh o/p (more quicker heat for the same £££s ? )

On a slightly variant note, is it 'better' to run a boiler near max or under run a larger boiler ? I have 6 rads running on this system.

HappyMJ

Cardew wrote: »

For some reason the EST always seem to exagerate savings in this field.



The average gas customer uses 16,500kWh pa.(that includes those cooking with gas) This at 4p/kWh will cost £660 pa. before discounts for dual fuel, payment by DD etc

So if the EST's estimate of average saving per houshold is £300 'Based on a saving of 25% gas usage'. the figures simply don't add up.

Even many 30+ year old boilers according to SEDBUK have an efficiency of 65%.

The average gas user now has an efficient boiler....it was only 5 years ago when the average gas usage in the UK was 20,500kWh per year. It's not that the weather has got warmer it's the average household is replacing old boilers with new boilers and improving insulation measures. Someone with an old boiler might be using 20,500kWh a year and could reduce that to 16,500kWh a year by changing the very old boiler and improving insulation.

Ben84

DUTR wrote: »

Just re-checked mine
16.6kwh i/p and 11.7kwh o/p
the replacement 12 HE is 13.3kwh i/p and 12kwh o/p 'suggesting the same heat o/p for less i/p?
Or the solo 15 HE 16.9kwh i/p for 15.2kwh o/p (more quicker heat for the same £££s ? )

On a slightly variant note, is it 'better' to run a boiler near max or under run a larger boiler ? I have 6 rads running on this system.

I'd ask your installer about sizing as they'll do some calculations based on your house. It may even be that you now need a smaller boiler if your house has undergone significant insulation improvements since the last one was fitted. However, I would suggest asking them about modulating boilers. We had one installed at our last house and I was very impressed with how well it worked. Many boilers simply have one setting, on or off and they turn on and off repeatedly to deliver less than their maximum output during lower demand. A modulating boiler however turns the gas up and down to match demand. Our installer thought it more efficient, I actually don't know the details on that point, but having used it I can say that it did an excellent job of heating the house evenly. When you turn it on it runs at full capacity to heat the house quickly, then the flame turns down to maintain the temperature and it just keeps the radiators warm.

C_Mababejive

I too have my doubts about the claimed 25% saving. As others have said,you cannot conveniently also discount such things as cost of new boiler,installation,annual contract as they are expensive to repair, the limited life of new boilers etc.
My annual gas usage is probably about 10,000 Kw pa and i am in the business of managing it down so i wont be rushing to ditch my boiler. In fact ill keep it going until it falls of the wall !

daveyjp

Ben84 wrote: »

I'd ask your installer about sizing as they'll do some calculations based on your house. It may even be that you now need a smaller boiler if your house has undergone significant insulation improvements since the last one was fitted. However, I would suggest asking them about modulating boilers. We had one installed at our last house and I was very impressed with how well it worked. Many boilers simply have one setting, on or off and they turn on and off repeatedly to deliver less than their maximum output during lower demand. A modulating boiler however turns the gas up and down to match demand. Our installer thought it more efficient, I actually don't know the details on that point, but having used it I can say that it did an excellent job of heating the house evenly. When you turn it on it runs at full capacity to heat the house quickly, then the flame turns down to maintain the temperature and it just keeps the radiators warm.

Most modern condensing boiler will be modulating as the water temp of the heating circuit can be set. Once set the boiler provides just enough heat to keep the temperature at the set level, thus reducing gas consumption.

Ours operates at a burner level of 12.5 or 25% of max output to maintain the set temp.

Cardew

Ben84 wrote: »

I don't trust those ratings so much any more. I looked up mine and noticed that everything seemed to be 65% efficient, which raised suspicions. I eventually found my answer. Anything with a standing pilot light gets 65% stuck on it.

For actual figures, your boiler manual should contain details on heat input and output which you can do the maths with. The installation does affect efficiency too, positively or negatively, so it's not a definitive answer to how well your system is using fuel, but it's a better answer than the SEDBUK ratings.

Excellent - thanks! That is very useful.

My boiler( Ideal Mexico super CF125) was fitted in 1988 and according to SEDBUK that was the last year they were manufactured; so early models will be 30 years old.

The detail shown on SEDBUK is an annual seasonal efficiency of 65% for both SAP2009 and SAP2005.

[FONT=Arial, Helvetica, sans-serif]SAP [/FONT][FONT=Arial, Helvetica, sans-serif]2009 annual efficiency: [/FONT][FONT=Arial, Helvetica, sans-serif]65.0%[/FONT][FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif]SAP [/FONT][FONT=Arial, Helvetica, sans-serif]winter seasonal efficiency: [/FONT][FONT=Arial, Helvetica, sans-serif]66.0%[/FONT][FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif]SAP [/FONT][FONT=Arial, Helvetica, sans-serif]summer seasonal efficiency: [/FONT][FONT=Arial, Helvetica, sans-serif]56.0%[/FONT][FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif][/FONT]
[FONT=Arial, Helvetica, sans-serif]Comparative hot water efficiency: [/FONT][FONT=Arial, Helvetica, sans-serif]37.7%[/FONT]

[FONT=Arial, Helvetica, sans-serif]SAP [/FONT][FONT=Arial, Helvetica, sans-serif]2005 Seasonal efficiency: [/FONT][FONT=Arial, Helvetica, sans-serif]65.0%[/FONT]




[FONT=Arial, Helvetica, sans-serif]Power: [/FONT][FONT=Arial, Helvetica, sans-serif]36.64kW[/FONT]

The performance data from the boiler handbook is

Minimum input 39.96kW: Minimum output 29.3kW that gives an efficiency of 73.3%.

Maximum input 46.1kW and maximum output 36.64kW and that gives an efficiency of 79.5%.

Presumably they must estimate the consumption of the pilot light(which admittedly is something of a flame thrower!!) and modify the 79.5% figure??

The conclusion must be that a high user(which entails the boiler running for longer periods) will be well above the 65% figure, and conversely a low user will be below 65%??

Any idea what the 37.7% figure represents?