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  1. #1
    Join Date
    Dec 2004
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    New to combustion analysis, have questions

    I was wondering if you guys would be willing to answer a few combustion questions please.
    I am the only in house HVAC tech for our company and I do have a boiler license plus almost 40 years doing HVAC. But very new to working on boilers.

    So, that all being said, just got my new Testo 3302-LX and am trying to learn as much as possible so that I don't feel like I've wasted our company's money.

    I ordered the only book I could find called Combustion Analysis and Fuel Efficiency by Erik Rasmussen, wish there were more I could buy.
    Also downloaded the PDF from truetech tools and read that many times. I have yet to see any kind of guide on how to actually use a analyser.

    Our company has multiple boilers some are the type that have a linkage gas and air, others just your standard 3.5 inch manifold pressure gas valve.

    the 1st day trying out the new tool I checked a Laars pool boiler type mighty therm. it's a natural draft type. here is a link to a picture of the boiler
    https://www.laars.com/products/product/mightytherm-ap

    It occured to me that the dilution air that mixes with the flue glasses AFTER combustion is not the same as our other boilers that the air mixes with the gas at the burner.

    So, when testing for for CO, CO2, O2 and NOX/SOX on natural vs mechanical draft how should I interpret the readings?

    Next question.
    Seems to me, all boilers (maybe not condensing?) would benefit from a high CO2 / low CO with of course low CO readings.
    I would think that I should always strive for more CO2% than CO and get my excess air as low as possible without going into the rich side which would cause a CO problem.
    So, if the above is correct, do I really need to use any manufacturer's info other than gas pressure. I was told that I need to get the combustion ratios recommended by the manufacturer.

    Last question.
    My new Testo gives me diluted CO as well as undiluted CO readings. I understand that diluted gas is after the burners, but where exactly do they refer?
    On smaller furnaces, the gas and air mix before the burner and then immediately after the burning but before the heat exchanger.
    Other heaters the gas mixes with air after the burner but before the heat exchanger. And then there's our natural draft boilers like the Laars that the gas and air mix before and then again after the heat exchanger.
    Am I supposed to be only checking the flue gasses at the flue regardless of what type of system it is and using the diluted vs undiluted readings?

  2. #2
    Join Date
    Jul 2007
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    Quote Originally Posted by alikair View Post
    I was wondering if you guys would be willing to answer a few combustion questions please.
    Let me start by saying congrats on getting into the area combustion analysis. You will be a better tech for it.

    Trying to answer all that is required to know about this subject can’t be done in a few paragraphs.

    Your best learning tool would be attending a National Comfort Institutes (NCI) course on “Combustion Performance and Carbon Monoxide Safety” - https://www.nationalcomfortinstitute...ex.cfm?pid=943
    There is no other course out there that can compare to this one.

    Even though this a Tech to Tech forum, it is an “OPEN” forum, and we do not go into specific details on how to test each piece of equipment. Natural draft and Induced draft / Condensing furnaces have different testing locations and different flue temperatures.

    The CO and O2 numbers for most equipment is the same - STABLE CO of less than 100 ppm (as measured), and O2 between 6-9%.

    Just knowing the numbers are outside the normal parameters doesn’t tell you why it is outside those parameters, and more importantly, what you need to do to correct the appliance back into normal and safe operating conditions - that is what the NCI course will do for you.

    I would also suggest applying for “PRO” status on this forum, which will give you access to the "LOCKED" Pro forums, where we will go into more details about combustion analysis questions and how to correct the problems you are seeing.
    Instead of learning the tricks of the trade, learn the trade.

  3. #3
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    New to combustion analysis, have questions

    CO is what you want to use. Not CO(o)

    Draft is also important.

    CO should be under 100ppm and stable
    O2 can range from 3%-9% depending on what style burner
    Non-condensing. Flue temp can range anywhere from 300-600*

    O2
    CO
    Flue temp
    Excess air

    Most important numbers. All the other ones dont matter


    Sent from my iPhone using Tapatalk

  4. #4
    Join Date
    Dec 2004
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    Thread Starter
    Quote Originally Posted by gravity View Post
    CO is what you want to use. Not CO(o)

    Draft is also important.

    CO should be under 100ppm and stable
    O2 can range from 3%-9% depending on what style burner
    Non-condensing. Flue temp can range anywhere from 300-600*

    O2
    CO
    Flue temp
    Excess air

    Most important numbers. All the other ones dont matter


    Sent from my iPhone using Tapatalk
    Thanks for the reply.
    What about natural draft vs mech does it mater where you take the readings? I would think all the extra air entering the flue with a natural draft system would give a much greater O2 reading than say a power burner

  5. #5
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    Quote Originally Posted by alikair View Post
    What about natural draft vs mech does it mater where you take the readings? I would think all the extra air entering the flue with a natural draft system would give a much greater O2 reading than say a power burner
    Yes it does, you have to take your combustion readings prior to the draft hood on natural draft appliances.
    Instead of learning the tricks of the trade, learn the trade.

  6. #6
    Join Date
    Apr 2006
    Location
    mechanical room
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    I always follow the manufacturers specs. up to a certain point

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