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Analyze my combustion analysis

NYplumber Member Posts: 503
Good afternoon wallies,

First and foremost, I owe a thank you to Tim McElwain for his great knowledge base that he shares and teaches.

Next, onto my analysis. Truth be told, if you don't test, you don't know.

The boiler is a dry base cast iron boiler, ~150mbh with a built in draft hood. All readings except for draft were taken before the hood.

First readings after a 10 minutes of running:

O2 2.8%

CO 1276ppm

Eff 77.4

CO2 10.2%

T-Stk 581*f

T-Air 66.3*f

EA 13.6%

CO(O) 1474ppm

Manifold gas pressure was 5.25"wc.

Readjust to correct manifold pressure, cleaned burners, vacuumed below burners, removed the broken reflective insulation off the bottom, and readings fell into place.

Took three separate analyzer readings. Draft was -.03"wc.

O2 6.6%

CO 38ppm

Eff 75.3%

CO2 8.1%

T-STK 578*f

T-AIR 71.9*f

EA 41.2

CO(O) 52ppm

O2 6.4%

CO 42ppm

Eff 74%

CO2 8.2%

T-STK 626*f

T-AIR 72.6*f

EA 39%

CO(O) 61ppm

O2 6.4%

CO 53ppm

Eff 75.7%

CO2 8.2%

T-STK 575*f

T-AIR 74*f

EA 39%

CO(O) 77ppm

My guess is that some of the CO showing up is actually NOX. As far as I know, Bacharach doesn't have a NOX filter.

The high stack temp is most likely poor heat transfer from sludge on the water side, or thin film of dirt on the fire side.

Comments and criticism welcome.


  • JStar
    JStar Member Posts: 2,752

    The high stack temp could also be a slightly high draft as well. You can see the excess air go down as the temp goes down. With a draft hood, there is no way to control that. Did you take a draft reading right out of the boiler?
  • NYplumber
    NYplumber Member Posts: 503

    The boiler has a built in hood, not a bell shaped diverter. The draft reading was taken about 18in above the boiler before any bends.
  • Tim McElwain
    Tim McElwain Member Posts: 4,628
    Thank you for your kind


    It looks like the boiler was way over-fired with a manifold pressure of 5.25" W.C. setting that to the correct (I assume 3.5" W.C.) made a big difference.

    Yes most testers will give a slightly higher CO air free than say a Testo which has a NOX eliminator. Such an item is available from Bacharach as an add on to the Insight meter.

    I like to try and take a draft reading before and after the draft hood to insure we do not have "Curtain Effect". You can use a digital manometer inserted down into the area just above the sections on boilers and furnaces with built in draft hoods.

    The other solution here would be to block off the existing draft hood and install a barometric so that draft can be balanced and this would also reduce excess air.

    Still another that I use is to cut in a draft reducer after the draft hood as close to the chimney as you can get. This is often in the past called a "neutral pressure point adjuster" or some old timers called it a "guillotine". I have the procedures on how to do this if you contact me by e-mail.
This discussion has been closed.