boiler rating

[nookncranny]

Can someone please explain how a boiler can be over 100 percent efficient?,british gas have told me this but when asked all she said was the new boilers are condensing which exceed 100 percent.
Do the newer boilers put out more heat than what is going in?

 

[Whitespirit66]

Probably referring to their engineers.

 

[45yearsagasman]

And I bear a striking resemblance to Brad Pitt.

 

[Boilerman2]

THis is absolute Rubbish - it is technically possible for a condensing boiler to give an efficiency of over 100% but this just a quirk of how flue gas analyzers work and circumstances also have to be right I have seen this happen a couple of times for this to occur the following conditions have to exist-
1. Heating system water has to be VERY COLD!!!
2. Boiler has to be room sealed balanced flue with concentric flue.

When the boiler is first fired (oil fired ones especially) it is possible that the flue exit temperatue is lower than the air intake temperature - Flue gas Analysers measure FLUE LOSS. so if the air going in to the boiler is higher than the air coming out, the analyser will see a FLUE GAIN, it simply adds this gain to 100% so will record 104% for example.

However this happy state of affairs is short lived, because as soon as the return water starts to get warm, so the flue exit temperature rises above the air inlet temperture and so the analyser sees a FLUE LOSS which it deducts form 100% i.e. 97%

Any Combustion efficiency testing should only be carried out after 15 mins or when flow & return pipes have reached their normal operating temperature.

sorry it's a bit long winded, but it is difficult to put into words!!

 

[Whitespirit66]

And I bear a striking resemblance to Brad Pitt.

As long as it's not his brother, Cecil!

 

[monoxide62]

Sales gimmick thats all.......................if you were told your new boiler is 100% efficient (nett CV) then in reality it would be somewhere around 90% efficient (gross CV) .......................blame the Germans for this.

Seems the Vaillant 600 series has a SAP rating of 100.3%.

 

[muggles]

As Boilerman has alluded to, it's a quirk of how efficiencies can be measured, however if you look at the SEDBUK efficiencies you'll see that very few boilers break 90% efficient in reality.

 

[45yearsagasman]

I was never up on all the technicalities of combustion/efficiencies, but I would listen to anybody who can explain how you can get in excess of 100% from a boiler. The laws of physic dictate that there is always some loss from the combustion process.(flue loss,etc)
I understand the example that bm2 used but surely that does not make the boiler 104% efficient? Am I missing something?
Regards Brad Pitts double

 

[Agile]

Of course you can never get anything more out that you put in! Basic laws of physics.

Unfortunately, some people have deduced ways to calculate efficiency using flawed methods and boiler makers have jumped on using them to make their efficiencies look higher!

Tony

 

[monoxide62]

I would listen to anybody who can explain how you can get in excess of 100% from a boiler. The laws of physic dictate that there is always some loss from the combustion process.(flue loss,etc)
I understand the example that bm2 used but surely that does not make the boiler 104% efficient? Am I missing something?

Total tosh as you say , gross calorific value of a fuel is defined on the basis that water vapour produced by complete combustion is subsequently converted into the liquid state , considering heat output of a fuel can never exceed heat input it goes to show efficiencys will always be less than 100% when referring to GCV , net calorific value of the fuel is based on the water content of the flue gas remaining in it's vapour state.

If we look at two identical boilers , one with an efficiency rating of 88% (GCV) , the other being 96.8% (NCV) , quite easy to fool the unsuspecting using simple maths....88 x 1.1 = 96.8%................96.8 x .91 = 88%.

94% x 1.1 = 103%.