Spare part for an old balanced flue boiler

[MikeJhn]

Guys

Modification of any fuel burning appliance is strictly forbidden unless you have the approval from the original manufacturer

If you want more efficient boiler change it don’t start modifying your existing one

 

[Riley]

Sounds a proper bodge to me

 

[Riley]

Not defensive. More apprehensive. You’ve been told by some extremely knowledgeable and professional guys what not to do and you seem hellbent on doing it anyway to save money

 

[Riley]

I assume that’s from an engineers fga print out? You have to be sure that your “improvements” are not making your boiler unsafe. Were it me I’d be speaking to the manufacturer to see how far you can modify it to not impact its actual designed functionality

 

[SJB060685]

Unfortunately with older non condensing boilers you’ll be hard pushed to get much better. Regular routine servicing is about all you can do. The next option is a new boiler with up to date system, although I am aware that not every customer can afford this.

 

[MikeJhn]

The original manufacturer is no longer around so impossible to check, the FGA readings confirm the boiler is safe and almost at ideal readings. I have had the FGA readings up to just over 85% but this was on a day with a relatively high air density.

 

[SJB060685]

As you know efficiency is calculated through the CO2% and flue gas temperature. You may get that reading one service and slightly different the next. Like I said regular servicing is the best bet, nozzle replacement, correct pressure, proper cleaning of baffles, filter changes etc etc etc will all add up. Also it’s worth adding and I don’t know if you know this but during the colder months you would set the CO2 slightly lower and in the hotter months slightly higher as ambient air temperature has a direct affect on CO2 and as you know too high CO2 results in increased soot and smoke emissions which will also lower the efficiency over time. Obviously a fully pumped and thermostatically controlled system will reduce over all fuel usage as well. The thing you have to remember is and certainly with older boilers they’re not designed as well as a modern day boiler and flue design so the MI’s might recommend a CO2 of 11% for example, where as modern boilers will be slightly higher due to better design.

 

[MikeJhn]

The MI's manual does not recommend any CO2 settings and I get the best response from this boiler running it at near 12%, O2 is 4.7% and the CO is 3ppm, excess air 29.0% so I think all in all its as near to what is optimum for this unit, as I said the whole exercise was to try and get the efficiency as high as I can.

 

[SJB060685]

That’s the thing, each boiler is different and you come to learn how each one likes to tick over. That’s some good readings, is it sooted up much come each service? It doesn’t matter wether you set up to O2 or CO2, they’re relative to each other. 12% CO2 is about 4.6% O2 which is what you have. Obviously CO2 and excess air etc etc change with fuel and calorific value, not that it’s relevant but I had considered moving abroad with my knowledge so what I’ve said above would differ slightly with different grade fuels

 

[MikeJhn]

Soot readings are 0-1 evidenced by the very little soot to clean off the inside of the chamber and baffles, for your information its air density not temperature that makes the difference to CO2, if you wish to know anything about Mazole as supplied in France ask away, that is where my other boiler is that I service.

From my notes:
Excess air is a calculation from the O2 reading not a separate measurement. 5% O2 is always 30% excess air, 7.5% is always 50% excess air, O2 on oil should be between 4%:6%.

 

[SJB060685]

I’m attaching an Image which I’ve always thought of when setting CO2.

 

[MikeJhn]

I have the same graph, one of these days I will publish my notes on setting up a boiler, (not trouble shooting) but it would not be popular as with the right equipment it shows how easy it can be, the hardest part IMO is the pressure on your knees.

 

[SJB060685]

I’ve been fortunate enough to have been trained by some very good guys. I was always told to adjust accordingly to outside temperature. If the air is colder this means it’s more dense (density is mass per unit volume). My understanding is in relation to this graph is in colder temperatures you set boiler up to a lower CO2 because when the temperature increases the CO2 will as well. If you set CO2 to 12% in -5 weather come summer this will increase accordingly, ultimately resulting in a sooter.
And I agree with what you said about CO2, O2 and excess air, it’s all relative so like you say 12% CO2 is going to be around 4.6% O2 and 29-30% excess air.

 

[MikeJhn]

This is also an interesting chart, unfortunately in deg F, deg C equivalents underneath the chart.

According to the humidity of the air the density will decrease. The addition of water vapour to air (making the air humid) reduces the density of the air, which may at first appear counter-intuitive. This occurs because the molar mass of water (18 g/mol) is less than the molar mass of dry air (around 29 g/mol). For any ideal gas, at a given temperature and pressure, the number of molecules is constant for a particular volume. So when water molecules (water vapour) are added to a given volume of air, the dry air molecules must decrease by the same number, to keep the pressure or temperature from increasing. Hence the mass per unit volume of the gas (its density) decreases, so testing in Oman would be totally different to testing in a dry African state.

 

[ShaunCorbs]

See first post