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cracked heat exchanger help

heatmiser Member Posts: 16
was wondering in everybodies experience , other than visually detecting it what are some sure signs of verifying without completely dismantling the furnace. i've heard a wandering draft and of course sooted vents windows etc. any other tricks i can learn???



  • Brad White
    Brad White Member Posts: 2,398
    edited February 2011
    Combustion Meter

    Not sure of the details but you should have zero products of combustion (obviously) in the air side. (I presume by "furnace" you mean forced hot air, correct?)

    Put your Testo, Bachrach, TSI, whatever analyzer you use to good use here and fast. Test the combustion side and the supply side of the fan and the return side of the fan. That is where I would start and I am sure others have much more direct experience.

    Soot on the vents and windows? All of a sudden?

    The living space and the basement should have CO detectors. That is code in MA but is good practice everywhere else. May even be code where you are, but it is cheap insurance.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • TonyS
    TonyS Member Posts: 849
    Combustion analyzer

    I cant speak for the others but a UEI combustion analyzer has an exchanger test mode. It takes a sample before you turn on the blower and then after you turn the blower on. It compares the two and tells you if its bad.
  • icesailor
    icesailor Member Posts: 7,265
    Testing HX'ers

    One sign is to have a good draft gauge in the chamber or breech and start the burner, Note the draft. When the fan blower fan starts, and the draft gauge shows a change in draft, it usually means the HX is cracked.

    Something else you can try is that the fan will run without the burner running. Set the blower to run on manual. Take a bottle of peppermint oil and pour it into the chamber. If the fan runs for a while and you start smelling peppermint in the house, you probably have a cracked HX.

    If you think you may have a cracked HX, you probably do. Warm Air furnaces are cheap. Cheaper than your life. Change it. It will pay for itself.
  • Tom Blackwell_2
    Tom Blackwell_2 Member Posts: 126

    Agreed; there should be no chang in combustion readings when the fan starts. This includes the flame pattern-you can sometimes see a particular flue passage upset the flame. The real danger here is having an influx of air into the combustion area and causing a large amount of CO generation, which can either go up the stack or roll out of the burner area. Testing with an analyzer is about the best way to ascertain this.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    No soot is good soot...

    If you have soot in your environment, SOMETHING is seriously wrong.

    Ellis Prach (Google that) once told me that if the heat exchanger is more than 5 years old, he guarantees that it IS cracked somewhere. Will the crack contribute to the production or distribution of CO? Probably not, but the code doesn't stipulate replacement ONLY if it is producing CO. It states that if the heat exchanger is cracked, it MUST be replaced.

    I hope you have numerous good working CO detectors throughout your house. The presence of carbon is not a good thing. Seriously.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • icesailor
    icesailor Member Posts: 7,265
    Cracked HX Help:

    If it's oil fired, here's another way you could check, based upon what someone said about the flame pattern changing.

    Use a Multimeter on Ohms and connect it to the Cad cell wires. You must jump out the control and connect directly to the Cad Cell wires while jumping out the FF terminals. Start the burner and when it starts, notice the Ohm reading while the burner is running and warming up the HX. When the fan starts, it the reading jumps or changes and stays changed, it is leaking. You can not always see the change with your eyes but the meter will.Pull the jumper and let the furnace fan cool it down. Reconnect the cad cell wires to the FF terminals and turn it back on. I can't tell you what the readings should be because it depends on what the Cad Cell is "seeing" when it is running. As long as it "sees" enough light, it will continue to run.

    Just another way.
  • billtwocase
    billtwocase Member Posts: 2,385
    The air filter

    is also a tell tale sign in most cases. As others have said, over fire draft before and after the blower is energized. A change towards a positive DOF will help to confirm a crack. When in doubt, rip it out
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