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Temperature probe inside chimney or on stove?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by DougA, Dec 13, 2012.

  1. DougA

    DougA Feeling the Heat

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    I'm buying a heat alarm for my older Vermont Casting wood stove that comes with either a probe sensor that requires a 1/8" hole drilled into a double wall chimney OR a surface mount sensor. My main concern is forgetting the damper and allowing the temps to get way too high. After 25 yrs of operation, we've been safe but have had some close calls. Since sensors are now available, I'd like to be safe. I fully understand that they will have two different temperatures and i can adjust to that but which one is better?

    If I get the probe for the chimney, it will interfere with cleaning the chimney and probably will get gucked up with residue which may affect the readings but in the event of a chimney fire, it would provide the best alert.

    If I get the surface sensor, I would attach it to the stove and the readings should be very close to the thermometer that I use now but I'm not sure if it will alert me in the event of a chimney fire.

    Can't get both unless i buy 2 alarms. Appreciate your suggestions?

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  2. bag of hammers

    bag of hammers Minister of Fire

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    Don't know what the sensor flue probe looks like but the temp probe (at least the model I have) slides out easily to clean the pipe (except when I have a brain fart and forget to do so and run the brush down into it - duh). Not sure if that helps at all...
  3. tfdchief

    tfdchief Minister of Fire

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    I have burned wood for 40 years and was flying by the seat of my pants for most of that time. I still have an old stove/insert in the fireplace and use a surface/magnetic mount thermometer on it. But I use a probe thermometer in the flue on my new stove and find it to be most useful. I guess because it reacts immediately to change in temps. I like it. But I think it is all relative and you have to learn what the temps mean in relation to your stove and operation.
  4. DougA

    DougA Feeling the Heat

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    Thanks for the replies. I ordered one with the probe and I'll report on it's operation when I have tried it.
  5. WES999

    WES999 Minister of Fire

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    If you can only get one, get the flue probe. I have both, flue temp alarm and stove top temp alarm.
    http://www.hearth.com/talk/threads/...tove-and-flue-temperature.95075/#post-1256138
    see post #8

    Flu temp can rise quite quickly and exceed the max recommended temp ( usually 1000::F) ,
    A temp alarm can warn you if the flue is getting too hot.

    You must remember to remove the probe when cleaning or it will get bent, ( did that once ;sick) .
    I just clean off the prob once in a while with some scotchbrite.
  6. bag of hammers

    bag of hammers Minister of Fire

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    whew - I am not alone...
  7. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    Probably covered but I have flex for my insert and have surface thermos on the front but use a laser for the pipe. How accurate is the reading from the surface of the pipe compared to the internal temp?
  8. Highbeam

    Highbeam Minister of Fire

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    Nope not alone. I pushed the brush right through my probe once too. The rutland poly brush made it around the probe without bending anything but I felt pretty dumb.
  9. bag of hammers

    bag of hammers Minister of Fire

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    Also have a poly brush but managed to mangle the probe enough to make it a throw-away. Sometimes I feel as dumb as, well, a bag of hammers...
  10. PLAYS WITH FIRE

    PLAYS WITH FIRE Minister of Fire

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    Bueller......Bueller


  11. DougA

    DougA Feeling the Heat

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    Thought I should update the thread. I rec'd the probe and ended up putting it in the short piece between the stove and the Tee before the upright chimney, so it doesn't require it to be moved as only the upright chimney gets cleaned on a regular basis.

    I have been amazed at the readings from the probe. Stunned is probably a better word. When the stove is burning steady, the probe is identical to the thermometer on top. Makes sense. However, when I am refilling the stove and there is still some wood inside and I open the damper just prior to lifting the lid to refill - OMG - the temps go over 1000 deg in a matter of 4 seconds while filling with wood. WOW Never would have guessed. As soon as the lip is shut and the damper goes down, temps drop to normal just as fast. This happens almost every time.The thermometer on the stove top doesn't even flinch in that short time.

    So, to answer the question on surface vs probe, it's identical on normal burn, not even close when the fire is rising or falling. The surface of the cast iron stove takes a long time to react to changes. The probe alerts you to problems fast enough that you can react if you are watching the LED readout or within earshot of the alarm.

    The problem I have is that I have an older VC stove without any glass front and I prefer to refill with wood before everything is burned down to embers. If I wait, it takes quite a while for the fire to get going again. edit: usually refilled at 300 deg or lower, so it's not as if it's a full burn. Also, the temp when the damper is down and it's going well are usually 450 range in my set-up. Both probe and surface temps are the same at that point. I'll post pics if someone wants to see.

    So, the probe and alarm have been a fantastic investment so far. Once I get used to the accurate temps, i should be able to determine the best time to refill the stove without the temps going nuts. Of course, I've been doing that without knowing for nearly 30 years of use so it's obviously not causing a problem.

    For those interested and because I searched high & low to find a good unit that was affordable, the link it here. They shipped same day as ordered and everything was as promised. There are 2 models, one that accepts a remote alarm and the one I bought with the alarm built in. Alarm is loud enough if you are in the same room but if you are in a bedroom and a deep sleeper, it is not going to wake you up. Instruction manual is pdf online only. I paid about $70 with probe and shipping.
    http://www.auberins.com/index.php?main_page=product_info&cPath=17&products_id=281
  12. Dakotas Dad

    Dakotas Dad Minister of Fire

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    I have a slightly different set up than most.. But I use a probe that goes into a box I made to offest my stove. The probe generaly shows about double what the IR says on the box surface. Early in the burn, there is an almost 1 to 2 ratio, later it gets a little closer, not sure why. Right now, late (5 hours) in a three split morning load, the probe is showing 200f, the IR says the outside surface of the box right by the probe is 122f, stove top at 270f. And most importantly, house at 72.


    [​IMG]
  13. Highbeam

    Highbeam Minister of Fire

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    I love the brick. That spot would be perfect for a steamer since it will get hot hot hot.
  14. DougA

    DougA Feeling the Heat

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    Gotta add one more thing.

    The alarm just went off a few minutes ago after I loaded the stove again. Damper up, stove top thermometer reading 375, probe reading well over 1000 and climbing very fast!

    I normally don't close the damper until the thermometer reading is at least 400. Hmmm. Still learning.

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