A Probe Thermometer

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BunkerdCaddis
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Post by BunkerdCaddis » Sun. Mar. 13, 2016 11:30 am

Finally got around to getting one of these probe thermometers

>>> http://www.amazon.com/dp/B00DYC7UYA/ref=wl_it_dp_o_pd_nS_ttl?_encoding=UTF8&colid=28VZQ2CSMWJTA&coliid=I22WZQ95189BM5

and installing it. Can't say exactly what I was expecting other than higher temps on it than on the skin of the flue pipe. I must say I am mildly surprised at what I have observed, yes much higher temps when stoking the fire (dampers open) but how quickly that temp drops when I shut down to an idle. As much as 300* in 5 minutes and another 100* in the next 10 minutes. Beyond that though what was a eye opener is how low the flue gas temp gets over an extended period of slow burning, down to almost 200*. I've only had it in a short time so long term conclusions are yet to be determined.

Attachments

coal temp1.jpg

Flue Skin Temp

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coal temp2.jpg

Stove Face Temp

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coal temp3.jpg

Stove Top Temp

.JPG | 105.1KB | coal temp3.jpg
coal temp4.jpg

Flue Probe Temp

.JPG | 106.5KB | coal temp4.jpg

 
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lsayre
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Post by lsayre » Mon. Mar. 14, 2016 6:29 am

People who measure only the surface temperature of their flue are missing a huge part of the story.

 
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Post by 2001Sierra » Mon. Mar. 14, 2016 12:45 pm

My experience, I too was surprised how the internal temperature was so much higher.

Attachments

Thermometer.JPG

Surface temp, mechanical, infrared, and probed

.JPG | 158.5KB | Thermometer.JPG

 
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Post by Sunny Boy » Mon. Mar. 14, 2016 1:06 pm

Glad to see they've come down in price. Does it come with paperwork that gives a range of accuracy over the scale of that 200-1000 F range ?

Edit. Ok I see where the Amazon ad says accuracy is plus or minus 20 degrees.

FYI. There's a thread on this a while back when it was said that skin temps were useless for gauging stove performance.

Using my K-thermocouple and IR gun, I posted how over a range of operating temps comparing the pipe skin temps to flu gas temps, consistently ran 1.9:1 to 2:1 ratio. I thought at the time that maybe that as the flue gases got hotter, there would be a limit as to how much of that heat the pipe could shed. But within the range of the stove idling, to running it's hottest for cooking, it stayed within that ratio.

So for those with just an IR gun they can come very close to finding out what the stove pipe flu gas temps are by simply multiply the skin temp by 2.

But then, the big question is what to do with that flue gas temp info ? If flue gas temp has some greater value than skin temp, should it only be compared to the firebed temps, not the outside of the stove ????

Paul


 
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Post by BunkerdCaddis » Mon. Mar. 14, 2016 9:54 pm

Sunny Boy wrote:There's a thread on this a while back when it was said that skin temps were useless for gauging stove performance.
If I remember correctly, I had just started thinking about a probe thermometer when that thread started. I was frustrated by the wild inaccuracy of the magnetic spring thermometers and had gotten an IR one but was still concerned about the amount of heat going up the pipe. The coal I have this year (Lehigh) idles very well and I get low flue temps. When I empty the ash out I let the ash door open to flash the fire up before adding more coal, I quickly get 400* or so on the probe which the skin temp never sees, add coal and damp down and just as quickly the probe is starting to come back down. So I am beginning to see it as a much more responsive window into what the stove is doing.

The thing that has surprised me most though is the sub 200* temps I got this evening on the probe, I never expected the flue gas to go that low, and that's still at 311* on the stove. (yes I have CO detectors, 3 of 'em I just don't have the magnahilic set up yet). But with 13 feet of stove pipe there can't be much heat left. I may have to get a probe for the top. :gee:
Sunny Boy wrote:But then, the big question is what to do with that flue gas temp info ? If flue gas temp has some greater value than skin temp, should it only be compared to the firebed temps, not the outside of the stove ??
For now I see it as a better gauge to what is going up the pipe, drawing more than that from the info may be beyond me. :?

 
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Post by corey » Thu. Apr. 07, 2016 12:57 pm

Is 400 internal cruise temp high for ky lump coal?

 
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Post by Lightning » Thu. Apr. 07, 2016 5:00 pm

The pipe radiates flue gas heat as it makes its way to the chimney. I believe the best reading then would be the flue gas temp just before the chimney.

Don't forget though that the chimney needs some of that heat to create draft so trying to extract all of it really isn't practical.

I would agree that some type of extraction method would be practical during times of high heat demand when more heated air mass is leaving thru the chimney as a direct result of the required addition combustion air to feed the fire. During times of idle when a low volume of air mass is moving thru the stove, a method of heat extraction may cause a draft failure.

The closer you can get the flue gas temp to ambient temp, the more you close the gap on thermal efficiency.

I have an idea of how to extract that flue gas heat as it passes thru the pipe. I may just explore that possibility next year. :)

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