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CO detection over the fire in an oil furnace

Hey all, i have read through a couple posts on this forum, and found a lot of info (some helpfull, some not so much). Here is my big question, followed by a little bit of a story with smaller questions:

What amount (ppm) of CO should i see over the fire/in the test hole in my smoke pipe on a typical oil fired furnace?

Here is the deal. My local fire department went to a non-customers house and told the home owner there was 150ppm detected in the home, she of course developed an instant headache and went to the hospital with her daughter (both of whom tested fine). The fire department shut down the furnace and told her she has to get it replaced. I went to the house once they had returned from the hospital with my CO detector and my pitch book full of new furnaces. I turned on the detector out side ("fresh air") and entered holding my breathe (not really). The detector stayed steady at 4ppm as i walked around the home (taking note, electric stove, dryer and water heater) and approached the furnace. I fired the furnace and stuck the probe of the detector into the supply plenum, 6ppm, 8ppm touched 9ppm and dropped back down. Took both clean out covers off, stuck in the probe 6,8,9 again. Stuck the probe into the smoke pipe and got a high reading of 14ppm. So... i called the fire department (as much as i like getting my comission check, i have a hard time condemning a unit that seems to be running proper) and waited as they sent over the "co-chief". I met the co-chief who was about my age (28) if not younger. His story was they got less than 40ppm in most of the house but when they got near the furnace the meter jumped to 150ppm. His thought was possibly a hole in the chimney? bringing flue gasses back to the unit and causing a build up by the unit over time? is that possible? is there something more i should have checked?

p.s. I have a chimney guy in the area who i trust, he is going out today at some point to check the chimney, untill he has the chance to get in there i have the unit shut down (it's about 70 degrees here.). If he says it is all good i have no reason to believe she shouldn't fire it up again... am i missing anything?

Thanks all in advance


(excuse my spelling and grammar. heating cooling and math... not english. lol)

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  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505

    Judging by your post, I think the following....

    1. 14ppm is not high in the smoke pipe, actually kind of low unless this is a new furnace.  Burner might be out of adjustment.

    2. The fact that you were reading 4ppm in the rooms means (to me) either:

    a)  you have a cracked heat exchanger

    b) the cleanout ports werent attached properly (or loose or missing gaskets).

    This is supported by the fact that you picked up some CO in the plenum.

    As far as the chimney, did anyone check the draft?  Or do a complete combustion analysis of the unit?

    I would have the chimney guy check (with a camera) and do what he has to do to certify the chimney is fine. It's probably going to need to be lined.

    Then I would pull the burner, open up the plenum and do all the things we do to look for a crack in the heat exchanger.  If it visually looks fine, I would proceed to do a complete service on the unit--the works, including pump pressure, vacuum cleaning, check all components, nozzle etc.

    Id get my personal UEI CO detector zero'd out in fresh air, go in the house with my combustion equipment, and fire it up.

    Let it run 10 minutes, checking ambient CO, then check/adjust draft, smoke test, and adjust with combustion analyzer.  If everything is good, and there's no ambient CO, you're good to go.

    I would stress again, especially in this instance, to zero out your personal CO monitor, and wear it the whole time.  You wanna know if its kicking out CO right away.  If so, shut it down, open the windows, go out to your truck and get your 'new furnace' literature out.

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  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    CO & Oil

    It is usually unlikely that when testing homes or equipment after the fact that we can expect to get the same results unless there is a really continuous, serious problem.   Most CO problems develop and worsen over time.

    Testing for CO in plenums only indicates that you are circulating CO unless the test was taken before the blower came on.  If the furnace is only making 14ppm it would have to dump 80% of that into the plenum for you to get a reading of 8 or 9 ppm. 

    If there is a barometric in the flue you know the flue has a big hole in it.  However the pressure in the flue is normally negative.  If there are flue gasses leaking in other parts of the flue then they would most likely be spilling at the barometric.  A draft test would be an important test to take. 

    When testing for CO on any furnace the testing should be at 3 minutes to 5 minutes long and the CO checked to make sure it is the same the whole time.

    I don't really  trust fire departments and their CO skills.  Two days ago they told a homeowner to replace the battery in their CO alarm because that is why it was going off.  The occupants were in the hospital the next day, severely CO poisoned, one unconscious.

    Someday everyone will realize that determining the cause of CO problems takes a few more diagnostics skills than they may think.  Too often I hear "there is nothing to it"  Wrong.
  • ZerbeAM
    ZerbeAM Member Posts: 6
    Thanks guys

    Both posts were very helpful. I have been asking around to a lot of the people i know and trust as well. It seems like the big thing i am going to want to do is a full combustion test (especialy draft). She was a non-customer, and the furnace did not look like it was being maintained on a regular basis.

    @Steve The furnace was not showing any signs of a cracked heat exchanger, i.e. no oder, no back preasure, no soot at any registers. I think i will try to zero out my detector again, 4ppm is next to nothing so i wonder if it may just be a little off. It sat right around 4 as i walked room to room.

    @Jim i couldnt agree more, the co-chief seemed to change his tune about how/where they detected the CO as i talked to him. Sadly he did not bring his detector with him when he met me on site.

    She was going to get back to me today with the results from the chimney guy, i will probably give her a call this after noon just to follow up. I guess more than anything i was confirming that i didnt miss anything of a critical nature. It does not seem like i did. I did not charge for yesterdays call, maybe i will recomend a good cleaning and a retest (just to be on the safe side).

    Thanks very much to both of you, great feedback, if you think of anything i may want to check please just let me know. @Jim again, i agree... i take CO very seriously. i would rather visit and revisit and revisit again than let a problem go.

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  • icesailor
    icesailor Member Posts: 7,265
    CO and Oil Furnace:

    Unfortunately, if a fire personnel made that call, he may have been wrong. I would get him back with his instrument to make sure it is properly calibrated. I heard of one somewhere that hadn't been calibrated since it was bought a few years ago.

    As far as cracked heat exchangers. here is a way I would try to check.

    Lock out the burner so it won't run. Turn on the manual fan and let the fan run for some time. Then, do one or both of these things. Make the burner run with the fuel shut off and the safety by-passed so the burner motor and fan will run continuously. Get something like wintergreen or peppermint oil and pour it in the chamber. Wait a few minutes to an hour with it running. If you smell the odor in the house, there is a break in the HX. Its best that you go outside for a period of time before you go in to test for smell.

    You can do a "Peppermint Test" to test for plumbing waste leaks but it is carefully prescribed. The person doing the sniffing can't be the same person pouring the oil in for the test.

    I was once told that numbers for oil for a good standard is:

    CO2    11.5 to 12.5

    O2        4% to 6%

    Excess Air     25% to 30%

    CO      Under 50%

    Every system is a little different. I have to play with the numbers to get happy. You can get soot at low CO too.
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