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Thread: Carbon Monoxide

  1. #1

    Carbon Monoxide

    I utilize a handheld UEI CO detector when I do my service calls. it is sensitive enough to go down to one part per million. I have held the detector at the opening of the external flue pipe of a 92 percent furnace and have only read a high reading of 13ppm.
    Hypothetically if the furnace had a crack in it would the supply air read this high of a level of CO?
    In cases of hair line fractures of the heat exchanger would any CO be detected?
    In a situation where CO is leaking into the occupied space do the levels build up thus increasing the ppm count?
    So in this case will the furnace need to operate a length of time to obtain a realistic walk around reading?
    What is proper technique in using my detector in conjunction with furnace operation to get a thorough assessment of outputs and to protect my clients.

  2. #2
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    You should always run the appliance for 5 to 10 min sometimes longer before doing your analysis. A reading of 13 ppm is fairly typical for a 92 percent efficient furnace also, I havent been in the trade long but done alot of furnace installs and generally on a high efficiency furnace the co reading in the flue is 10-20ppm usually.
    Id really like to hear what more experienced guys have to say about this.

  3. #3
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    On any induced draft furnace, the heat exchanger will be under less pressure than the blower air. If the HX is cracked, the blower will force air into it and out with the flue gases. Not the other way around. However, it can also cause the burner to roll-out or burn improperly, causing CO to back out of the HX and into the furnace. In both cases, you would not typically see CO in the blower air stream (unless you have an open return at the furnace).

    You also need to be measuring CO-Air Free, not just CO. The difference is dilution. If you think of the amount of exhaust from the flue as a cup of water, and the amount of air from the blower as a gallon of water, you could have the same amount of CO in both, but you'll read it in different concentrations because they exist in different volume ratios. The CO in the blower air will read much less, even though it is the same absolute amount.

    The only way to diagnose a cracked HX is with a combustion analysis and/or visual inspection.

  4. #4
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    12-13 ppm co As read tells me you're awfully underfired. You don't have to measure air free, it's not telling you anything different, it just makes it more confusing. If you're below 100 ppm as read and completely stable, the unit is burning correctly and safely. Try getting your o2 down to 7-8 percent, you're prob around 15% right now... You'll drastically increase thermal efficiency and reduce fuel consumption, abbot 7-8% and youll notice less stress marks on the heat exchanger.

    AlsO, uei makes junk :/ try the testo 327

  5. #5
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    Many Tech's do not take into consideration:
    Customer smokes or the whole family making for a constant 7 to 10 PPM.
    Start their car in the garage with the door open and then back out after first ten two twenty seconds = 1,000 to 5,000 that hangs around up to an hour before dilution down to under 100 to a smokers 7 to 10 ppm. R/Air wrap of co back into S/Air leveling out at a constant reading barely noticed. Outdoor Termination wrap on two pipe set up.

    You have to look deeper than an analyzer or visual.

  6. #6
    I have found an inspection cam has worked great. I have had hair line cracks that doesnt seem to affect the flame and doesnt show co leakage. Just last night i looked at a furnace that was red tagged for a cracked collector box and I was asked to fix it. Being an 18 yr old goodman i looked a bit into it. With the inspection cam i found an 8" hair line crack. The nice thing with the cam, you can show the home owner and even better is being able to show that the other company missed the exchanger ( bit of a price diffrence of a collector cover and a furnace ). Has anyone used the Hetkit trace gas method for exchanger leakage and whats your view on it?

  7. #7
    Join Date
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    4,761
    let us presume you are using a personal CO detector/monitor and not a Combustion Analyzer.

    you CANNOT rely on the monitor to give you a reading from the flue gases!!!!!!

    the ONLY way to measure the flue gas CO is with a CA!!!
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  8. #8
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    Quote Originally Posted by Gross View Post
    12-13 ppm co As read tells me you're awfully under fired. You don't have to measure air free, it's not telling you anything different, it just makes it more confusing. If you're below 100 ppm as read and completely stable, the unit is burning correctly and safely. Try getting your o2 down to 7-8 percent, you're prob around 15% right now... You'll drastically increase thermal efficiency and reduce fuel consumption, abbot 7-8% and you'll notice less stress marks on the heat exchanger.

    Also, UEI makes junk :/ try the Testo 327
    what do you base that on?

    for example, a Pulse furnace can be as low as 5PPM in my personal experience.

    CO is NOT a specific number is good or bad, but rather a range. also, as you stated the other numbers are just as important and have a direct effect on each other.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  9. #9
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    Quote Originally Posted by Gross View Post
    12-13 ppm co As read tells me you're awfully underfired. You don't have to measure air free, it's not telling you anything different, it just makes it more confusing. If you're below 100 ppm as read and completely stable, the unit is burning correctly and safely. Try getting your o2 down to 7-8 percent, you're prob around 15% right now... You'll drastically increase thermal efficiency and reduce fuel consumption, abbot 7-8% and youll notice less stress marks on the heat exchanger.

    AlsO, uei makes junk :/ try the testo 327

    There is no way to accurately monitor combustion based on CO alone. And by bringing the O2 levels down, you'll most likely be raising gas pressure, so your fuel consumption will go up. I've never had a drastic increase in efficiency either. Maybe a swing of 3% either way. Most times, you lose efficiency by trying to make adjustments to meet environmental standards. It's just a trade off we make. I try to get my O2, CO2 and stack temperature in range, then make changes to adjust CO.

    CO Air Free is the only CO reading that matters. There is a big difference in measurement. All regulations are based on CO Air Free. It tells you the exact number being produced. I've seen a CO reading of 60 and a CO Air Free reading over 100. My personal CO meter measures Air Free because I want to know exactly how much CO is in the air with me, not how spread out it is.

  10. #10
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    Quote Originally Posted by JStar View Post
    There is no way to accurately monitor combustion based on CO alone. And by bringing the O2 levels down, you'll most likely be raising gas pressure, so your fuel consumption will go up. I've never had a drastic increase in efficiency either. Maybe a swing of 3% either way. Most times, you lose efficiency by trying to make adjustments to meet environmental standards. It's just a trade off we make. I try to get my O2, CO2 and stack temperature in range, then make changes to adjust CO.

    CO Air Free is the only CO reading that matters. There is a big difference in measurement. All regulations are based on CO Air Free. It tells you the exact number being produced. I've seen a CO reading of 60 and a CO Air Free reading over 100. My personal CO meter measures Air Free because I want to know exactly how much CO is in the air with me, not how spread out it is.
    i couldnt disagree more. every percentage you lower oxygen is 1-2% increase in efficiency, you scrub the walls of the hx much better and get better delta Ts....

    i recommend a professional combustion course....nci has a really good one....your local supply house doesnt count.

  11. #11
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    Quote Originally Posted by JStar View Post
    There is no way to accurately monitor combustion based on CO alone.yep thats right And by bringing the O2 levels down, you'll most likely be raising gas pressure, maybeso your fuel consumption will go up.not nessasarly I've never had a drastic increase in efficiency either. Maybe a swing of 3% either way. Most times, you lose efficiency by trying to make adjustments to meet environmental standards.burner efficency has nothing to do with equipment efficency It's just a trade off we make. I try to get my O2, CO2 and stack temperature in range, then make changes to adjust CO. here i agree, just need to add temperature rise and blower CFM. then you'll have all the information you need for a complete analysis

    CO Air Free is the only CO reading that matters. There is a big difference in measurement. All regulations are based on CO Air Free. It tells you the exact number being produced. I've seen a CO reading of 60 and a CO Air Free reading over 100. My personal CO meter measures Air Free because I want to know exactly how much CO is in the air with me, not how spread out it is.
    your not 100% wrong, in fact you have many things right. but you really should listen to Mr. Gross. it's obvious to anyone who has taken a decent CO/Combustion class your not measuring efficiency correctly
    my boss thinks its possible to repeal the laws of physics

  12. #12
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    Make sure when looking at CO Air Free you keep in mind what it truly is.

    It is a calculated value from any instrument also measuring O2, it has the possibility of being off substantially depending on the programming of the instrument being used.

    If you are trying to determine if an appliance meets ANSI Z-21 certification then CO Air-Free is the only way you can do this based upon the certification criteria.

    The conditions that CO Air-Free exist under are a physical impossibility as the reading represents a CO reading with no O2 present in the flue gas sample.

    Things will be much easier from a dagnostic standpoint using as measured CO.
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  13. #13
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    Quote Originally Posted by Checksinmail View Post
    I have found an inspection cam has worked great. I have had hair line cracks that doesnt seem to affect the flame and doesnt show co leakage. Just last night i looked at a furnace that was red tagged for a cracked collector box and I was asked to fix it. Being an 18 yr old goodman i looked a bit into it. With the inspection cam i found an 8" hair line crack. The nice thing with the cam, you can show the home owner and even better is being able to show that the other company missed the exchanger ( bit of a price diffrence of a collector cover and a furnace ). Has anyone used the Hetkit trace gas method for exchanger leakage and whats your view on it?
    What camera do you use?

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