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Is this Flue Temp Probe Full of "It"?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by pen, Jan 21, 2010.

  1. Highbeam

    Highbeam Minister of Fire

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    How do we know that they aren't talking about surface temps of the stove? Or worse yet, that they just aren't very good at math and got caught in the somewhat easy to fall into trap of assuming since the outside of the pipe is 50% of the inside that the inside should be 50% of the outside.

    Who even knows anymore since condar makes pretty much all of the probe meters and their accuracy is now suspect? I would no sooner believe their instructions than would I believe their meters reading.

    I still expect the outside of the single wall to be half of the internal temp. This would be verified by noting that the overfire temp on the rutland is 550 which should correspond with 1000 internal temps which is the overfire temp for metal pipe.

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  2. Peter B.

    Peter B. Feeling the Heat

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    As of last year about this time, I'd used the same Condar probe for about 20 years and 'trusted' it to the extent that it provided reliable (if not highly accurate) readings.

    With my setup, I have one flue probe hole at 12" above the stove top and one drilling into the stove itself to read catalyst output temperatures directly. I used to switch the Condar back and forth to get relative readings.

    After twenty years' service, I thought it might be time to replace it.

    I splurged and bought <several> new Condar thermometers - both flue and catalyst probes, and a stovepipe surface thermometer.

    To my surprise, the new flue probe read about 200*-300* higher than the old one - switching them back and forth from the same location and letting each stabilize - during multiple 'test runs' on a fairly constant stove temperature.

    Needless to say, with such a disparity, I had no idea which thermometer to trust.

    I then bought a pair of identical long stem catalyst probes, figuring they were just 'ruggedized' flue models... hoping to find (at least) two thermometers that might (more or less) agree.

    Indeed, the catalyst probes 'agreed' - within 100* of each other... and within 200* of the new flue probe.

    The 'agreement' was determined by an (otherwise meaningless) oven test when I used three stabilized temps to compare the readings of seven (7) different thermometers of different types... including a rather old hardware store oven thermometer.

    Here are the results:

    Relative Thermometer Readings - Oven Test

    2/25/09

    Nominal Oven Temp - 250
    Oven thermometer - 270
    Stovepipe (surface) - 300
    Old flue probe - 640
    Small catalyst - 580
    New flue probe - 810
    Large cat 1 - 860
    Large cat 2 - 900

    Nominal Oven Temp - 300
    Oven thermometer - 330
    Stovepipe (surface) - 350
    Old flue probe - 820
    Small catalyst - 720
    New flue probe - 1060
    Large cat 1 - 1140
    Large cat 2 - 1140

    Nominal Oven Temp - 500
    Oven thermometer - 510
    Stovepipe (surface) - 500
    Old flue probe - 1300
    Small catalyst - 1200
    New flue probe - 1700
    Large cat 1 - 1880
    Large cat 2 - 1780

    -----

    From the above, it's easy to see that the oven trial IS (in fact) meaningless when it comes to 'testing' probe accuracy... though the surface thermometer was in pretty close agreement with the actual oven temp... but that's when it's completely 'immersed' in a constant temp within the oven... not sitting on the stovetop, exposed to ambient air.

    When all was said and done, I felt confused and defeated... unable to determine which (if any) of the thermometers could be described as 'accurate'. For most of the rest of the season last year, I just used the old flue probe in the same location... because I knew what to expect in terms of the live fire and catalyst operation.

    This year, I swallowed hard and gave the nod to the paired cat probes... but know they aren't particularly accurate either as catalyst light off isn't reliable until the stove internal probe reads better than 1000*.

    So... much as I'd like to have a fairly inexpensive ACCURATE thermometer, I guess I'll have to go on dreaming.

    Peter B.

    -----

    Attached Files:

  3. karri0n

    karri0n New Member

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    Up until now, this thread, the probe thermometer has been the end-all in terms of accuracy; if someone was getting funky thermometer readings, the answer was "try a probe type". It now seems a very specific set of curcumstances needs to be met in order for these to be accurate. What's worse is that there seems to be no simple way we can test the accuracy of these models:

    It's assumed that, for double wall pipe, a probe type is the only viable option for accuracy. If the device is designed for double wall, and the bimetallic element is located directly behind the face, it makes sense as to why using it on single wall pipe will get a much higher reading. However, given what we have learned in this thread, how can we possibly test the accuracy of these units in a double wall setup?

    The standing belief that internal temps on single wall will be double the external temps has now been challeneged, and there has never been an accurate ratio for external to internal pipe temp on double wall. This means, in a double wall setup, we cannot use an external thermometer to compare the results to the probe thermometer. Comparing probe temp to stovetop temp might be a viable option, except that the ratio of stove top temp to pipe internal temp will vary wildly from stove to stove, and will be very dependent on how efficiently the stove is radiating the heat into the living space, whther the stove is using a blower, and where exactly on the stove top we are reading.

    Even Peter B's test has shown that the accuracy of these things has a decent amount of swing even between two units of seemingly the same model.


    Consider the waters very troubled at this point. This thread has shattered quite a few assumptions for two pages.
  4. begreen

    begreen Mooderator Staff Member

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    I'm not sure that is a valid test for a flue probe. They are not a simple coil thermometer are they? Could be wrong but I would think that heating up body would give erroneous results. Holding them, probe only in a known high temp environment would seem a more valid test for this kind of thermometer. Maybe boiling water - 212 °F, a barbecue lid vent in a hot barbecue? or perhaps a low propane flame??
  5. pen

    pen There are some who call me...mod. Staff Member

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    Just straightened out the face/dial on the "broken" one that was initially sent to me and put it in place of the replacement. Same exact readings.

    The best results testing it would come from me firing up my deep fryer. But instead I think,,,,,,, wait a minute.......... russet potatoes in the pantry.....

    :) :) :)

    brb

    pen
  6. Diabel

    Diabel Minister of Fire

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    That 900* looks high, I don't think it reads correctly. My stove top is cooking at 650* & with a probe thermo. 18" up (DW) it reads 600*
  7. Battenkiller

    Battenkiller Minister of Fire

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    OK, my curiosity has gotten the best of me. I think I've decided what I'm going to do.

    My IR thermo takes K-type thermocouple probes. On Monday I'll try to remember to get the one that my supplier recommends for the task. It should only set me back about $30 (donations will be accepted via Paypal, lol). I will drill a 1/8" hole and insert the probe, then take a simultaneous surface reading with the IR. Should be accurate to +/- a few degrees. At least that will give me a benchmark score at 18" above the collar for both internal and external temps. I'll share the results here. Then I'll put a sheet metal screw in the hole and use the external after that.

    And yes, I have a single wall pipe.
  8. pen

    pen There are some who call me...mod. Staff Member

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    That will be a great comparison. I can't wait

    pen
  9. pen

    pen There are some who call me...mod. Staff Member

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    Well, all I can say is these are my results. They are of course open to interpretation. I certainly hope nobody is using dial up :coolsmirk:

    Moved the probe higher up on the flue pipe

    [​IMG]

    Got everyone jumping at the party

    [​IMG]

    Would you like me to supersize that for you? BTW, the oil thermometer is reading 358 f

    [​IMG]

    Close up in hot oil

    [​IMG]

    And the every famous shot in the hot tub. BTW, when fully submerged and left in the boiling water, the probe cruised at 600 flat.

    [​IMG]
  10. Diabel

    Diabel Minister of Fire

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    I love that last pic!

    btw. How do you insert such large & high quality photos?
  11. pen

    pen There are some who call me...mod. Staff Member

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    I use the MultiFocus feature on my camera for close-up shots (it's the button w/ the flower on it) and I upload my photos to photobucket.com and then link them to here using img tags around their url

    pen
  12. begreen

    begreen Mooderator Staff Member

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    That pretty much says it. Based on what I'm seeing, I don't trust these new probes.Wonder if they got a bad batch?
  13. pen

    pen There are some who call me...mod. Staff Member

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    That's why I say it's open to interpretation. Is it possible that the probes can't be accurate in the circumstances I just placed them in? Do they work some other way that I cannot consider? They do have a bimetalic strip coil behind the dial. I'll post a pic here in a minute.

    pen
  14. begreen

    begreen Mooderator Staff Member

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    Yep, they do, I just checked that out. Seems like very bad calibration or the wrong coil on them.
  15. pen

    pen There are some who call me...mod. Staff Member

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    [​IMG]
  16. Diabel

    Diabel Minister of Fire

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    Thanks!

    I use my phone & then upload through the forum. Next time I will use my camera & upload through the pb. It sounds like a lot of work though....
  17. pen

    pen There are some who call me...mod. Staff Member

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    Any else out there willing to hard boil their probe thermometer so we can compare the results?

    Your wife will only think you are nuts for a little bit. Well, unless of course you really are nuts then she'll continue to think so. But if that's the case,,,, meanwhile, back at the ranch.

    Mine read nearly 500 when it was submerged in boiling water up to about an inch from the face.

    It read 600 when fully submerged.

    pen
  18. WES999

    WES999 Minister of Fire

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    I just checked my Fisher that's burning as I type. Single wall pipe. The Condar magnetic thermometer is reading about 340 °F , the thermocouple probe is reading about 550 °F ,
    I checked the Cnondar with a digital surface probe and it read about 310 °F .
    (BTW the pic is an older one taken when the stove is not running.)
    It sure looks like your Condar probe is reading high.
    I think a digital probe is the way to go.

    Attached Files:

  19. Battenkiller

    Battenkiller Minister of Fire

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    Wes, that's about the same 50% difference BeGreen said it should be. Looks like his info from Condar is correct, but the maker's probes themselves are wrong... or at least this one is.
  20. pen

    pen There are some who call me...mod. Staff Member

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    Remember I've got 2 probes. The first one ordered came damaged (face was smashed) and the other is the replacement. For testing purposes I have fixed the face on the damaged one and both are reading similarly.

    Bad batch?

    pen
  21. Highbeam

    Highbeam Minister of Fire

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    I love the hot tub test and the fat test. I only wonder if since the coil is above the water/oil that the heat rising from the liquid is heating the coil. I would expect condar to design this probe so that the coil is in ambient air and not in the steam which is of course hotter. I am quite certain that the air temp around that coil will have huge effects on the coil as shown by simply blowing on the coil with lung power.

    I'm holding on to hope but am slowly starting to believe that these meters are crap.

    How can we adjust them? Any word from Condar yet?
  22. begreen

    begreen Mooderator Staff Member

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    I have tried to discount the testing methods, especially the oven method for testing a probe thermometer assuming the same thing. One would think that they may be adjusting calibration for ambient air cooling. However, that doesn't explain the large discrepancy when it is properly mounted on a flue pipe. It seems something is seriously wrong with this batch. My Condar probe is the old style with a solid black face. It's readings seem to consistently correlate with the stove top temps, but I may test it externally if we have a fire again this winter.
  23. Diabel

    Diabel Minister of Fire

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    I was boiling eggs this morning...& stuck the probe in the water expecting to read around 215* -------it read 410*!!! The steam must be affecting the temp!
  24. pen

    pen There are some who call me...mod. Staff Member

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    too much steam aye? BRB :coolsmirk:
  25. pen

    pen There are some who call me...mod. Staff Member

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    How about this.... Temperature inside of the cup was 160 when this picture was taken. No steam here.

    [​IMG]

    I just can't come up w/ any way to give credence to anything this thing is reading........ with one exception! It looks (in my estimation) to read correctly at room temperature at the bottom of it's scale!

    pen

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