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heat exchanger testing

Paul_69 Member Posts: 251
are than some good methods of checking heat exchangers.i have always used the draft gauge over the fire thru test hole and when blower comes on it would affect the gauge reading.i have found alot of leaks this way which i was taught a long time ago.but i had one the other day and it was showing no change but could detect oil odor thru vents. i pulled off back panel of furnace and found a good size hole in front of fire box. i know about candles but wanted to see what other techs. have had success with. thanks


  • billtwocase
    billtwocase Member Posts: 2,385
    edited November 2011

    a good electrnic combustion analyzer with show the change when the blower comes on, positive draft over fire with the blower running, or rip into them. I will disconnect the blower, pull it out, fire it off, and look for light. Some cracks may be towards the top. Pulling off the first take off, and fish around there. I haven't used candles in years. I will add the obvious which would be check all cleanouts, inner chamber access plates, and so on. A low boy that the flue passes thru the fan compartment, check that thoroughly too.
  • Tim_Hodgson
    Tim_Hodgson Member Posts: 60
    I have used both

    a draft gauge and combustion analyzer. very successfully, but of course I did find one that did not show a failure. I suspect the furnace pressure was equal to the blower pressure. I have since inflated a balloon in the flue pipe and set off a smoke bomb in the firebox until the smoke inside is stable, then turn on the blower. I have seen smoke come out the observation port and air being drawn in if the exchanger is breached. Just make sure there is no air leakage around the observation port to distort the visual effect.

    Give it a try and let me know if you have any false readings.

    Good Luck,

  • icesailor
    icesailor Member Posts: 7,265
    HX Testing:

    If there isn't soot coming out of the heat outlets or you are getting  "ghosting" from soot, I'd try this.  Get a bottle of Peppermint oil extract and pour it in the combustion chamber. Jump out the burner so the burner motor will run but not fire the oil. Have the fan come on. Give it the smell test in the house. Let it run for a while. If you start smelling Peppermint, yiou have a leaking heat exchanger.
  • Gary_17
    Gary_17 Member Posts: 37
    Smoke candles

    Work best for me. I have to confirm all bad heat exchangers as we have a free furnace replacement program. I sometimes check a couple a week. The first thing I do is get access to see the top of the heat exchanger by opening the plenum and lifting the A-coil a little . Sometimes I drill 2 holes w/a step bit or pull the humidifier. Always run the burner for a little while to heat the chimney to establish a good draft then I lift the smokepipe off the breach a little and seal it w/metal tape. Then I pull the burner and seal that opening. Throw the smoke candle in through the flame sight door and quickly seal that up. As soon as you see smoke in the plenum cut the tape on the breach to release the smoke up the chimney and poke a hole in the burner opening to help it.
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