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A combustion Analysis question

KCAKCA Posts: 300Member
Hello All...

  I have a Laars JVH160  Natural Gas (induced draft) Boiler with these readings.

CO2  5.8%

   O2  10.7%

   CO  25 ppm

  Draft .07

Seems off...  If I adjust the manifold pressure down from 4" the CO2 % goes down.. (Recommended by factory is 4.0")  seems like the CO2 is low and the O2 is high...  Draft should be in the negative...  Stack temp was 287degF... I clocked the meter and everything worked out well...  How do I get the readings in where they should be...  CO2 around 6.5 anyway and O2 at 7-9%....  I don't know why the draft is in the positive...

A bit confused...

  :-)  Ken


  • SlimpickinsSlimpickins Posts: 315Member
    need to

    Turn up your manifold pressure to raise the CO2 and the O2 willdecrease as well. You want to keep your CO under 100 ppm. CO2 on natural should be 8-9.5% and O2 6-9% for Natural gas or whatever the manufacturer says.
  • JStarJStar Posts: 2,668Member

    What draft meter do you have? Was it facing into the boiler or into the chimney? A positive draft could mean a blocked chimney.
  • KCAKCA Posts: 300Member
    The unit has a total

    of 5' of flue...  Blows right outside the mech room...  There isn't a blockage... 

    I can't turn the Manifold pressure up to much...  I played a bit and turned it up to 4.5" and the CO2 went to 5.9 maybe...  I couldn't leave the burner running that high though...  There really isn't anything else to adjust...

    I have a Bacharach  Fyrite Pro

      :-)  Ken
  • JStarJStar Posts: 2,668Member

    I don't think those burners have any adjustments.

    Sounds like too much primary or excess air. With such a short amount of venting, I think the inducer is drawing too much air through the boiler. I probably shouldn't recommend this, but I would mess around with blocking off the exhaust a small amount at a time to see if the numbers change.
  • SlimpickinsSlimpickins Posts: 315Member
    edited November 2012
    wrong orifice

    You might make sure the burners have the right orifice size,
  • KCAKCA Posts: 300Member
    I'm at 6000' ASL

    The unit has a # 47 DMS orifice...   So maybe a smaller one?

    The orifice clocks ok now... 


     :-)  Ken
  • SlimpickinsSlimpickins Posts: 315Member

    How many burners? I'm just under 6000' myself
  • KCAKCA Posts: 300Member
    I believe 7

    7 burners....

  • SlimpickinsSlimpickins Posts: 315Member
    adj. air shutters

    With a #47 orifice you probably have 8 burners

    After looking at a gas orifice chart with a #47 orifice you probably have 8 burners at 4. 0 w.c. If I remember right, the burners do have an adjustable air shutter. With your analyzer running, try closing the shutters a little bit and see if that brings the CO2 up while keeping the CO under 100 ppm

  • KCAKCA Posts: 300Member
    Air Shutters

    are wide open.....  And I double checked...  there are 7 burners...

    with a 4" water manifold pressure recommended by the manufacturer...   That doesn't add up..

  • JStarJStar Posts: 2,668Member

    Meter down on the burner shutters. That will bring your O2 down.
  • SlimpickinsSlimpickins Posts: 315Member

    Like Jstar said your 02 will go down and your CO2 will go up.
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