Combustion Analysis = Scam?
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  1. #1
    Join Date
    Mar 2005
    Posts
    4

    Question

    Hello,

    I recently had an HVAC guy out to check our furnace, which we had not been doing regular maintenance on. Our furnace is a well known name brand, lower-to-middle of the line, and about six years old.

    Anyhow the technician ran a "combustion analysis" test the yeilded the following CO info:

    CO 160 PPM
    CO AIR FREE 270 PPM

    Based on this information, the technician told us we had a very dangerous situation in terms of Carbon Monoxide leakage, probably due to a cracked heat exchanger. He advised us to replace the entire furnace immediately and offered to dispatch emergency technicians over the weekend to install one of thier "house brands" (their own furnace).

    Of course I got a second opinion and called an HVAC company that my family has used for over 15 years. He turned up no leakage externally and found 80 PPM in the exhaust vent. He pronounced our furnace safe but dirty.

    I called the original company back for a refund and spoke to the owner. He claims that he is one of the few companies in the area the runs "combustion analysis" tests, and that unless the second HVAC guy ran the same type of test, he wouldn't have detected the dangerous CO levels. He claims that we still have a very dangerous issue on our hands that should be tended to ASAP.

    Two things don't sit right with me:

    1. When I asked why there was no detectable leakage in spite of such high readings, he said that he didn't know why it wasn't showing up and then mentioned something about "negative pressure" in the heat exchanger.

    2. The original technician who was out told us that with the furnace being over five years old, that the heat exchanger probably wasn't under warranty any more, and that the cost for the part + labor would be about 2/3 of a brand new furnace. I later found out that most manufacturers have a 15-20 year warranty on the heat exchanger.

    My two questions:

    1. What are your thoughts on this combustion analysis test? Can anyone explain to me why the leakage is not detectable by any other test? Do they have a valid point?

    2. Should I report this to the BBB?

    Thanks!

  2. #2
    Join Date
    Jul 2000
    Location
    NW IL.
    Posts
    3,935
    First 160 ppm CO is high, normally the exhaust should run under 100 ppm. Now the difference between the reading of the first and second company. It is best to monitor the exhaust flue from burner ignition, blower turn on and burner off cycle, and also the vent draft. Hi co at burner on and warm up period can mean dirt, burner misalignment, overfiring etc. A rapid in CO or Oxygen levels when the circulator blower comes on indicates that the heat exchanger has leakage. Either from a crack, perforation, loose gasket or missing mounting screw for heat exchanger cells. If the co level rises slowly after the blower has been on for over a minute it may indicate that there still may be leakage, it could also indicate a venting problem. In other words if company A ran the furnace for over 10 minutes while testing and company B only ran the furnace for 3 minutes that would account for the difference in CO readings.

    Now for measuring co in the plenum. There are lots of variables when measuring co in the plenum. They are:

    A CO detector cannot tell you if a heat exchanger is good.

    A CO detector can indicate a heat exchanger is cracked only if all of the following conditions occur simultaneously:

    a. The flame generates enough CO (lack of oxygen, excess fuel, high temperature).

    b. Enough exhaust gases are emitted from the heat exchanger crack or perforation.

    c. The exhaust gases from the crack are not diluted too much before coming in contact with the sensor. A cracked heat exchanger may leak CO in a small stream. You may measure high concentrations only an inch away.

    d. The heat exchanger is the only possible source for the CO detected.

    Also depending upon the type of furnace you could have a penetration through the heat exchanger at one location and not develop CO in the plenum. But if the penetration were at a different location in the heat exchanger would allow co to leak into the plenum.


    What I am trying to say is just because that at the location in the plenum that was tested co was not present does not mean that a failure on the heat exchanger does not exist.

    If you having any concerns of the two conflicting results there is a verifiable test that can be performed to determine heat exchanger integrity.

    <snip>The American Gas Association developed FURNACE HEAT EXCHANGER LEAKAGE TEST injecting a nitrogen and methane gas mixture into the burner chamber. The heat exchanger outlet of the heat exchanger is plugged and a combustible gas detector is used to check for gas leakage on the exterior. A detailed fact sheet on the AGA test procedure is available at
    http://www.aga.org/pdf/publicinfo/co...facts8612b.pdf








    Dadgum ole furnace.




  3. #3
    Join Date
    Oct 2001
    Location
    Waterford Michigan
    Posts
    2,668
    What was the reading in occupied areas of the house?

  4. #4
    Join Date
    Mar 2005
    Posts
    4
    MechAcc: Thank you for the detailed response. I do know the the first tech did run the furnace for about 10-15 minutes. The second tech did run the furnace for less than 10 minutes. In either case, I now know that company has very possibly alerted me to a valid issue. I will read up on the Leakage Test info you provided and have the Exchanger tested. Thanks!

  5. #5
    Join Date
    Mar 2005
    Posts
    4
    Originally posted by johnl45
    What was the reading in occupied areas of the house?
    Edited: Company A only tested within the furnace. Company B did a sweep of the house with some wand type of sniffer. I didn't get any specific numbers, but he did say that he did not detect any high levels of CO.

    [Edited by zippy71 on 03-03-2005 at 12:20 PM]

  6. #6
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Here we go again I think MechAcc hit the nail right on the head. Not all cracked heat exchangers spill into the plenum, due to the combustion chamber being at negative pressure. If there is truly a crack this can be a dangerous or deadly situation. That crack can open up at any time and allow CO to enter the plenum, and then the house. Please take the first companies statement very serious. Yes there are some companies out there that use CO as a scare tactic to sell equipment. You need to find a good reputable service company, get references from friends and neighbors. Then have your system maintained regularly by the same company year after year. When you find a good honest company give them all your HVAC business, even if they are more expensive than other companies around, once you find a good company you don't want to let them go. Age of equipment is not the only factor, an improperly installed unit can fail in far less than 6 years. Others will post shortly, and I believe at least one is a teacher of CO safety testing.

  7. #7
    Join Date
    Oct 2004
    Location
    Texas
    Posts
    1,172
    RED FLAG. They already lied to you about the warranty period. Scam? A, YES.
    Saddle Up!

  8. #8
    Join Date
    Nov 2001
    Posts
    1,874
    Pay them to pull the heat exchanger to show you if the ht exgr has failed or not.

    Seeing is believing and peace of mind

    [Edited by Toolpusher on 03-03-2005 at 12:55 PM]
    If you try to fail, and succeed.
    Which have you done ?



  9. #9
    If the co reading was stable I would not worry about the heat exchanger. I agree with your second tech the furnace is dirty and needs a tune up. I have had many furnaces with co readings higher than 100 ppm in the vent. A simple cleaning and adjustment of the gas pressure cleared it up. If the level is rising I would be concerned about venting issues and this is a serious safety issue. I feel you are justified in complaining to the first company. Not a big fan of the scare tatic and emergency replacement crew deal.
    Brian

  10. #10
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,247
    Originally posted by zippy71

    Anyhow the technician ran a "combustion analysis" test the yeilded the following CO info:

    CO 160 PPM
    CO AIR FREE 270 PPM

    1. What are your thoughts on this combustion analysis test? Can anyone explain to me why the leakage is not detectable by any other test? Do they have a valid point?
    zippy,were the CO numbers the only readings that the two technicians took? A true combustion analysis includes taking other measurements in the flue gas besides just CO.

    A combustion analysis is the only way to be for certain that your fuel burning appliances are operating safely & efficently. The trick is it must be performed properly by someone who has received the proper training in how to interpret these readings.
    Individuals who have been trained properly should be able & willing to provide proof of their training.
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  11. #11
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584
    I would say that the first company was performing the right test, but not sure of the real readings.

    Might want to call around to ask for combustion anlaysis test. If second C.O. test fails ask them to check with factory on warranty heat exchanger.Most have 10 some 20 year warranty. But, labor is costly to repair heat exchangers as it takes several hours to replace.
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  12. #12
    Join Date
    Aug 2003
    Posts
    83
    I don't know about most of the techs on this board, but, when I test a heat exchanger, I test for delution of CO2, not CO, when the fan comes on????

    CO is a product of incomplete combustion and alerts you to a potentially serious problem.

    Just having that high of an extra air reading can produce high levels of CO...

    The extra air cools down the combustion gases and raises CO levels.

    The worse thing you can do for a FHA furnace is to NOT do regular maintenance on them.

    In my opinion it's the most common reason for system failure.

    Just allowing the HX to overheat from not changing those inexpensive filters leads to most early problems that I see.






  13. #13
    I agree with the other posts high co levels can be caused by most of the things mentioned. But the furnace is probably not the only appliance in your house that produces co. do you have any of the following?
    gas hot water heater
    space heaters
    electric or gas ovens
    attached garage
    many things can cause high CO levels but according to what you were originally told the co levels in the vent were high which usually leads back to maintenance or other issues. If the heat exchanger were cracked I think your co levels would have been much higher ( usually they are ). The only way to determine whether your appliances are safe is with an co analyzer. But just looking at one appliance is not the only thing you should do when you discover high co levels you have to take a "whole house approach" because the high levels may be coming from somewhere else. I had a customer use a leaf blower to clean out his attached garage and three days later the levels were still at over 35 ppm in the house and he had no gas appliances in the house. If the co levels were not rising in your appliance then it was probably not a cracked heat exchanger( I don't know this without examining it myself ) . If they could not be lowered by maintenance and the venting and combustion are correct then the only thing left is to disassemble the furnace and find a crack if it is there.

    I don't use CO as a scare tactic but shouldn't we get serious about it? look at some of the information on this website before you decide if it is a "scam" http://www.coexperts.com/

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