How much can temp probe placement affect the displayed temperature?

[williaty]

I have an Auber Instruments thermocouple stove pipe probe. I just moved to a new house and moved it from my freestanding wood stove at my old place to the fireplace insert/stove at my new place. Unfortunately, the correct placement for the probe (IIRC, 15" above the stove top) is up inside the chimney so the only place I could drill a hole for the probe is about 2" above the stove top.

I am getting terrifyingly high flue temp readings from this new stove. At the same time, the stove front temp as displayed by one of the cheap Rutland magnetic thermometers is reasonable. The inside of the firebox looks about like what I'd expect a happy secondary-air-type wood stove to look like in that it has healthy flames but isn't a crazy ball of fire. However, I don't have a lot of experience with wood stoves other than the first stove I had at the old place, so there's definitely a possibility that the stove looks like an inferno and I just don't recognize it.

So my question is, with my temp probe mounted a foot closer to the stove than it's supposed to be, how high of an incorrect reading might it be giving?

 

[begreen]

What is terrifying? The temps will be higher of course. How much is not certain. I would expect them to be about 100) higher than 15-18" above the flue collar. What you may be seeing is the effect of not turning down the air soon enough if the temp is exceeding 900º.

What stove is this? How tall is the flue liner on the insert? Where is the Rutland thermometer placed?

 

[williaty]

What is terrifying? The temps will be higher of course. How much is not certain. I would expect them to be about 100) higher than 15-18" above the flue collar. What you may be seeing is the effect of not turning down the air soon enough if the temp is exceeding 900º.

What stove is this? How tall is the flue liner on the insert? Where is the Rutland thermometer placed?

Rutland thermometer is stuck just above the right top corner of the door (hinge side).

Pacific Energy Super Insert Series D

I don't have an exact measurement for the flue height as the people who came out to inspect it didn't provide one. The chimney stops 2-3' above the 1-story plus attic-height gable end of the house.

First time it got high on me (which wasn't the worst, actually) yeah I might not have sat on it fast enough after the hot reload. Having that first scary experience, I have been clamping down hard on it after a reload and trying to keep it around 500F as it begins to burn. It'll stabilize somewhere between 500-550F with the throttle fully closed and burn nice and calm. Then 40-60 minutes into it, it'll suddenly go china syndrome and then temps will skyrocket fast. It's twice gone over 750F and once hit 860F. This typically happens at the same time the secondaries really kick in. It looks normal when it's doing this, which is what really confuses me. The Rutland will show either the high-green range or the veeeeery bottom of the red range (like not a full needle width into it) once the flue temp has been over 700F for 10 minutes or so.

Temps on the flue thermocouple are all over the place. Some of it makes sense. Like the post-peak coaling-phase temps I see pretty much line up with what I'd expect. However, there's that burst where all the fuel sort of gets to the off-gassing temperature all at once and those flare ups are reaching as high as 860F. The thing is that it doesn't look like 860F.

My previous stove was a Woodstock Ideal Steel. This stove is a considerably older Pacific Energy Super Insert Series D. The Summit looks like the Ideal Steel looked when the flue probe (properly placed on that one) would have read 575-600F when the too-close location on this stove is reading 860F.

I had 4 thermocouples in my Ideal Steel at one point. The firebox probe was interesting because it would swing 400 or more degrees in a matter of seconds depending on whether the flames in the box were mostly blowing towards the back of the firebox away from the probe (cooler) vs blowing towards the front of the box with the flames directly hitting the probe (hotter). I'm actually wondering if, as a normal part of the operation of this stove at the peak of the burn cycle, flames lick just a little bit out the top of the stove into the stove pipe and my unfortunate forced placement of the probe is catching that.

 

[begreen]

OK. the good news is that it doesn't sound like anything dangerous. The readings will be higher when so close to the flue collar. The high peaks are likely due to a bloom of flue gases and strong draft due to cold outside temps. Try closing down the air more aggressively and sooner as the fire gain strength.

 

[EbS-P]

I have a probe in the appliance adapter of a Drolet 1800i with a damper. I can not run it below 650-700. Just won’t happen. Medium it 800. And full secondary is 950. STT never get above 650.

So the answer is a lot. The blower makes at least a 50 degree difference. And almost another 50 low to high (too loud on high).

I would like to know what the temps are 15” above the stove but I’m not drilling a hole in the flex liner.