Opinions on Co2 readings

[MarkOil]

After chatting to a few other engineers, and not returning to any of my customers for a second service yet.
I just wondered how all you other guys set your Co2 on boilers.
I was told originally to set it to MI's in the summer, and 0.3% under in the winter.
I don't think that is too bad considering I service some boilers that are not in that bad condition and when I check the Co2 it's 1-2% under the MI's!
I'm just a little concerned in the back of my mind that after serving a boiler in the height of winter, will it 'soot up' in the summer?

Thoughts and experiences would be very grateful

 

[SimonG]

I never set to mi's. I like to see it at 11 to 11.5. But i dont use an analyser.

 

[MarkOil]

You serious? Has your nose got a built in analyser? lol

 

[Killy Bing]

Do you replace the nozzle?
The high pressure "tracks" the nozzle causing more fuel to enter.
so after the year with more fuel to burn but the same amount of air, you get less co2

 

[Dotty]

Mine are set to 11-11.5% too.

Also without an analyser......

 

[SimonG]

You serious? Has your nose got a built in analyser? lol

I use an old wet kit. Nose is good, but not that good

 

[MarkOil]

So basically you always set exactly to MI's?

 

[SimonG]

Std eff boilers tend to get a nozzle every other year unless it needs one. The condensers get one every year. Had issues trying to get two years out of them.

 

[SimonG]

So basically you always set exactly to MI's?

No. Some mi's ask for 12 or 12.5. Just asking for trouble. A lot of high exposed areas round my way. When i was being shown the mysteries of oil i was told in exposed areas to give it an extra 5 psi on the fuel and set between 11 and 11.5.

 

[Best]

The "wet & dry" old fashioned way is fine for setting an oil boiler, but no proof of settings.
Just need smoke pump, "egg timer" co2 tester & a gauge thermometer.
Don't try to match MIs.
Some are wrong & can even be bettered, but often you need the co2 at less than 12%.
I tend to set the co2 as high as possible on conventional tall flues, but lower co2 on low level flues.

 

[Best]

Do you replace the nozzle?
The high pressure "tracks" the nozzle causing more fuel to enter.
so after the year with more fuel to burn but the same amount of air, you get less co2

Should be the opposite effect - more oil volume means less air to oil ratio & therefore higher co2 & potentially higher efficiency if nozzle is still okay & co2 doesn't go too high & boiler gets overly sooty.
Personally, I don't think nozzles need changed every year, unless they are coated in dirt or nozzle filter gets dirty.

 

[Ermintrude]

? More oil same air = co and less co2 thus super sutty

 

[Killy Bing]

Should be the opposite effect - more oil volume means less air to oil ratio & therefore higher co2 & potentially higher efficiency if nozzle is still okay & co2 doesn't go too high & boiler gets overly sooty.
Personally, I don't think nozzles need changed every year, unless they are coated in dirt or nozzle filter gets dirty.

Im thinking more co less co2?

 

[MarkOil]

Well this is interesting, I tend to change nozzles every year regardless, if I didn't I would be paranoid muck from the cleaning process could of settled on the tip.
I think from this I shall probably stay as I am, been servicing these boilers a while now, and not had any problems so far, just wait until the second services to find out how they did.
At least I will now know the previous service history as I seem to visit a lot that have been looked after by bodge it a leggits, or no-one!

 

[Best]

Im thinking more co less co2?

More oil means really you have a reduced air to oil mix & will mean the co2 rises.

 

[Ermintrude]

More fuel means more hydrocarbons - more C in combustion mix, if O the same CO will surely be more prominent? Than CO2? CO2 will initially rise them fall after 10 mins and CO will rocket?

Not done any formal oil training just applied thinking and experience from not playing with oil fired appliances .

 

[Best]

? More oil same air = co and less co2 thus super sutty

No, - the more the oil increases compared to the air, will mean the co2 increases - that's if we are talking only small amount of extra oil!
Just like raising the oil pressure on an oil boiler that is sitting at say, 8bar pressure & 11% co2,
If you raise the oil pressure to 8.5bar without adjusting anything else, then co2 will rise slightly & perhaps to 12%. That's why I am saying that boilers gradually running slightly richer can actually be running more efficent if they don't get to a sooty burning stage! :smile:

 

[Killy Bing]

Hmm, i can see your point best. Saying that i mainly work on grants. Any increase on the co2 and hello co

no way is the analyser going in.

I've just found that if you set to mi's to get the efficiency then any increase in the oil pushes the appliance into incomplete combustion!

 

[Best]

More fuel means more hydrocarbons - more C in combustion mix, if O the same CO will surely be more prominent? Than CO2? CO2 will initially rise them fall after 10 mins and CO will rocket?

Not done any formal oil training just applied thinking and experience from not playing with oil fired appliances .

What I am saying is, a nozzle that is spraying oil in very high amounts compared with it's supposed output, or if it's spray pattern is very poor due to part blockage or bad wear, will obviously cause seriously poor combustion. BUT, slight raise in oil output through a nozzle will raise the co2 & if this co2 doesn't go much beyond 12 or 13% then the boiler may not soot up excessively or perhaps at all & may well be more efficient.

 

[Killy Bing]

What I am saying is, a nozzle that is spraying oil in very high amounts compared with it's supposed output, or if it's spray pattern is very poor due to part blockage or bad wear, will obviously cause seriously poor combustion. BUT, slight raise in oil output through a nozzle will raise the co2 & if this co2 doesn't go much beyond 12 or 13% then the boiler may not soot up excessively or perhaps at all & may well be more efficient.

the boulters were fine doing this thinking about it.

 

[SimonG]

Imagine having this discussion about gas on an open forum

 

[Best]

Imagine having this discussion about gas on an open forum

We would all have been expelled!

 

[Ermintrude]

Ok. You would need to measure the calorific output of appliance / hex surface temp. With increase in oil volume the vapour is cooler and sucks more energy to ignite so burn temp is lower ? I wouldn't want it to run ritcher probably leaner if honest but I don't do oil for day job as live in toon.

 

[Dotty]

We would all have been expelled!

D'you ever drink in the Central Bar in carrick?

 

[Best]

D'you ever drink in the Central Bar in carrick?

No, - why? Did they expel you? :smile:

 

[Dotty]

They did when I condemned their gas fire......

 

[Nostrum]

I agree with best on this one, as the fuel is atomised it is burnt fairly efficiently and there will be excess air to allow for the increase in fuel but the mix will be richer so co2 will rise (with a drop in excess air) with a very small amount of co rise.
Obviously to a certain point where incomplete combustion starts to kick in and then co will rise fairly rapidly.
I do think some of the manufacturers sail a little close to the wind so to speak but personally I stick to MI.

Ermi, what your saying would apply if you were already burning at a stoichiometric ratio or at the point the appliance can no longer burn completely (more likely)

 

[WHPES]

There are a number of variables:

Too much air and the fuel won't have chance to burn properly so more soot and CO
Too little air not enough oxygen so more soot and CO.
Too high pressure, too much fuel so more soot and CO
Too little pressure, too large droplets and feeble jet so more soot and CO
Flame spreader too near to nozzle, not enough vapour distribution so more soot and CO
Flame spreader too far back, ditto

As for CO2 readings, in theory, as high as you can without getting incomplete combustion (usually max of 12). MIs are a result of extensive testing. The lower the excess air, the better, provided your CO levels don't go up (increasing incomplete combustion hence less efficiency). The more excess air, the more air flowing through the chamber so less time you have for heat to transfer into the water so the more heat lost to atmosphere.

 

[lame plumber]

There are a number of variables:

Too much air and the fuel won't have chance to burn properly so more soot and CO
Too little air not enough oxygen so more soot and CO.
Too high pressure, too much fuel so more soot and CO
Too little pressure, too large droplets and feeble jet so more soot and CO
Flame spreader too near to nozzle, not enough vapour distribution so more soot and CO
Flame spreader too far back, ditto

As for CO2 readings, in theory, as high as you can without getting incomplete combustion (usually max of 12). MIs are a result of extensive testing. The lower the excess air, the better, provided your CO levels don't go up (increasing incomplete combustion hence less efficiency). The more excess air, the more air flowing through the chamber so less time you have for heat to transfer into the water so the more heat lost to atmosphere.

put together well to explain to all.

I change te nozzle annually no matter what, it makes me a couple of quid and the instructions tell you too

 

[Bunker]

Im with LP and Mark, new Nozz every time.

Condensers for me get about 11.3 and no higher, this will often give about 30 CO which is well under and an XAir of 34 ish.

Most of the SE boilers I go to for the first time are soot free with burnt out baffles, do a FGA and youll find CO2 of 8.5. I get this alot. Those ones I will up to 11% or under.

I like the above suggestion of a higher CO2 on taller flues, hadnt thought of that.

 

[Killy Bing]

+3 for always changing the nozzle.
and filters.

does anyone change the hoses each year?

 

[Best]

+3 for always changing the nozzle.
and filters.

does anyone change the hoses each year?

The way I look at it, if a boiler that is being run flat out all year by someone who needs or just loves a lot of heat, is okay to have a nozzle replaced once a year, then a boiler that is getting no more than average use a year will not need a nozzle replaced strictly every year. Also, a new nozzle can actually be faulty. But guess we can't argue with MIs really with regard to new nozzle.
The oil hoses are a difficult one - to replace every year seems unnecessary & wasteful.
Riello oil hoses probably should be renewed every 2 years max, unless they have obvious damage, but it's the claim & blame culture that makes some just replace them every time.

 

[Killy Bing]

The way I look at it, if a boiler that is being run flat out all year by someone who needs or just loves a lot of heat, is okay to have a nozzle replaced once a year, then a boiler that is getting no more than average use a year will not need a nozzle replaced strictly every year. Also, a new nozzle can actually be faulty. But guess we can't argue with MIs really with regard to new nozzle.
The oil hoses are a difficult one - to replace every year seems unnecessary & wasteful.
Riello oil hoses probably should be renewed every 2 years max, unless they have obvious damage, but it's the claim & blame culture that makes some just replace them every time.

ive noticed that flexis on tigerloops or if the pump is set for tank return the flexis always seem to be in a poor condition.

OH or when the last twit catches them under the burner on a downward firing worcester

 

[Bunker]

I replace hoses if they are looking a bit crispy. I only carry 2 types which I can use for everything;

1/4 angle M to 1/4 F straight Black
1/4 angle M to 3/8 F straight Green

I have them hanging in a tube so I use the colour as a code for which size.

I keep loads of various oil line fittings.

 

[Best]

ive noticed that flexis on tigerloops or if the pump is set for tank return the flexis always seem to be in a poor condition.

OH or when the last twit catches them under the burner on a downward firing worcester

There's a certain amount of heat generated from the oil pump on a tigerloop set up. That might not help the hose life. But I come across a lot of Riello hoses that are around 10 or more years old & seem to have lasted if not touched! Hoses from the electro oil burners are however a different breed & seem to last forever. As you said, usually some idiot twists them or damages them & you really need to replace.
I saw a tigerloop with Riello hoses that that had a leak on a hose & ruined a garden.