High CO2 Level

Just had my boiler cleaned and tuned. Had lots of soot that seemed to mostly accumulate over the summer. Not sure why ??

The technician adjusted the boiler, however, the CO2 left was left high - 13.5 to 14%. After reading various threads on this forum, anything greater than 12% is too high. And that is not counting what I read about "bad air days".

Other #'s on the combustion test were:

- Gross stack temperature 420 degrees
- Net stack temperature (his estimate) 350 degrees
- CO2 13.5%. Should be 11% to 12%
- Smoke 0
- Breech draft -.015
- Over fire draft -.007 Should be -.01 to -.02. Is this okay?
- Overall efficiency 85 3/4%

I've met with the oil company owner, and the technician will be coming back to make adjustments to lower the CO2 %.

Other than opening up the attenuation air band setting to give the boiler slightly more air, (and possibly slightly more smoke on the smoke test than 0, and a lower efficiency), what other boiler adjustments can be made to lower this CO2 %?

Thanks.

 

I'm missing something here. Generally you want the highest CO[SUB]2[/SUB] reading you can get with the lowest O[SUB]2[/SUB], CO and smoke readings. Lowering CO[SUB]2[/SUB] readings will not increase smoke readings and will almost assuredly raise the O[SUB]2[/SUB] readings as well as net stack temperature.

I DO question the results your technician got from the testing. I wonder how long it has been since his analyzer was calibrated to a known standard. 14% with no smoke at all would be phenomenal.

 

I believe that 14% is too high... I forget exactly why that is, but I think it's something to do with the 'stoichiometric ratio' of the combustion. At 14% CO2 you will have very little 'excess air' and that means that as the air density changes with the season, there is very little 'headroom'.

If the calibration of his instrument is correct, then it needs to be dialed back to around 12 or so.

 

The oil company owner is checking the technicians instrument and sending him out with 2 of them for comparison. He is using the old bubble type of test equipment.

From everything I have read, 14% is too high, AND will lead to soot. This is what I am trying to avoid this year.

And I understand that opening up the attenuation air band setting to give the boiler slightly more air will lower the CO2 level.

Okay, I had though the CO2 and O2 were inversely proportional. My wrong!

The technician does not have equipment for testing the O2 or CO levels.

Before the technician comes back, is there any other type of adjustment he can make to the system to lower the CO2?

Thanks again.

 

Hi josko, your last statement in post 1 is wrong. More air = less smoke. Your not in lab conditions and some things are subjective,like steady state.Imo a touch more air is the best option.

 

Read closer Josko, they ARE inversely proportional!

Let me rephrase it by removing the piece about smoke:

You mean the clear plastic thingy with the rubber hose on it? and the red fluid inside? Those are perfectly fine and accurate IF the fluid is not depleted AND he knows how to use it properly.

 

I am less concerned about the 14% CO2. It is a bit high but 12% to 13% is better.
My big concern is the draft. The OF draft should be around -0.02 - -0.04 (max) Anything above -0.04 will pull the flame off the head of the burnr and cause sooting and a noisy fire.
Get the draft down. Draft that high will also pull more air through the burner and drop the flame temperature.

 

Missed the draft readings. Two zeros after the decimal point for over fire? Need more breech.

 

I questioned the accuracy of the 13.5% CO[SUB]2[/SUB] reading along with zero smoke. The only time I have seen a CO[SUB]2[/SUB] reading that high with with zero smoke was on an industrial boiler in a dry ice manufacturing plant. That boiler was run primarily for CO[SUB]2[/SUB] production and had a specially designed furnace that maximized the CO[SUB]2[/SUB] production but at a loss of maximum efficiency.

Nothing inherently wrong with the wet "dumbell" analyzer but I question any company that uses them over an electronic analyzer. Not doing oxygen, carbon monoxide, sulpher dioxides and nitrogen oxides is, in my opinion, not doing your job as a burner technician.

 

The specs for my burner note -.01 to -.02 W.C. draft in combustion chamber, i.e. over-fire draft. Mine was -.007.

There are no specs for the stack draft, however, a google search suggests it should be -.02 to -.05. Mine was -.015.

While both are not in the range, if rounded off to 2 decimal points they would be.

On Wednesday, the technician will be back and will teat/make adjustments.

- From the above data, does the barometric damper need to be adjusted?

- Other than the attenuating air ban setting, is there any other adjustment that will help lower the CO2?

 

My oil burner tech did come back out last year. Besides rechecking the system with a second wet "dumbell" analyzer, he adjusted the attenuating air band setting from 5.25 (spec is 5.5) to 6.5. The results were:

10/1/15 cleaning test results followed by 11/18/15 adjustment test results
Gross stk. temp 420, 410
Net stk. temp 350, 350
CO2 13.5% (high), 11.5%
Smoke 0%, 0%
Breech draft -.015, -.01
Overfire draft -.007, -.001 (the spec is -.01 to -.02)
Efficiency 85.75&, 84.75%

The boiler will be cleaned in 2 days. The smoke from the chimney is white. Soot build-up on top of the boiler is almost nothing over 14 months. The flu pipe looks (to me) to be fairly clean, with no real soot build-up.

So, without seeing the boiler with the top off, the soot problem that existed prior to the 10/1/15 cleaning seems to have been resolved.

The flame looks good to me, but I'm not the tech.

The overfire draft is still too high.

I had asked the tech to adjust the barometric damper some last year; he said it did not need adjustment.

I'm thinking that because changing the draft would effect the CO2 reading, that he did not want to make any adjustment to it. OR possibly, as he noted, while it was not in spec, it was close enough to be insignificant.

I also understand that too much draft can "increase heating appliance operating cost by venting heat out through the chimney instead of transferring the heat into the building where it was wanted. Too much draft can also increase chimney temperatures to an unsafe level."

So should the barometric damper be adjusted to let in a bit more air for proper vent vacuum, or is what I have okay given the data above, especially since I have negligible soot?

I'm thinking the barometric damper should be adjusted slightly to get more within spec range, but I'm not a tech.

 

Any feedback?

Cleaning will be done this a.m.

thanks

 

Changing the setting on the barometric damper changes ALL the draft readings. Since the draft at the breeching (the point where the furnace/boiler connects to the stack is acceptable you do NOT want to change the barometric damper setting.

The overfire draft is NOT high, it is low, mind the decimal points! This is most likely caused by air leaks into the combustion chamber. Or maybe the "technician" doesn't know how to read the draft gauge.

 

I want to know what kind of draft gauge he's using to measure 3 decimal places.
Increasing the combustion air will reduce the overfire draft.
With the breech draft being low, adjusting the barometric to allow more vacuum would be a good place to start. The down side is the stack temp will likely increase thus reducing efficiency.
Are you sure the tech is using the factory spec'd nozzle? Some boiler/burner combinations are very picky about their nozzles. Change brands (even with the same rate, angle, & pattern) & combustion readings can change significantly.

 

Boiler was cleaned yesterday by a new tech; I was frustrated with the last one (not worth going into). This new tech was efficient and more knowledgeable than the last one.

The boiler, when inspected, was very clean. After 14 months, the flue pipes had no soot build-up of any sort, the chamber was clean, and the top flue sections had little soot on them.

I can not agree more. WG04 boiler . For years, I used a Delevan 1.10 70 B, recommended for my Weil-Mclain QB180 burner. Any other nozzle resulted in problems. A more recent version of their manual listed a Delevan 1.00 70 B; I've used this for the last 6 or so years.

Post cleaning, the numbers for this year are:

Gross stk. temp 400, was 410 last year
Net stk. temp 350
CO2 11.5%
Smoke 0%
Breech draft -.01
Overfire draft - barely on the negative side of 0
Efficiency 84.75%

Good question - an analogue gauge with a needle. Easy enough to read -.01 or -.02. Anything else is just 'eyeballing' it. I asked him about possibly adjusting the barometric damper; he was comfortable with the breach reading (as also noted by Furd), and said that as long as the overfire draft was not positive, that was okay. The needle was registering just slightly on the negative side of 0. Probably where the -.001 from the prior year came from.

So my concerns has been addressed.

Thanks again Furd and Grady.