How much can temp probe placement affect the displayed temperature?

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?

 

Having it that close to the stove will make a huge difference...it's probably actually in the flame early on.
In that setup you'll just hafta figure out what normal is for your setup.

What temps are you seeing?

 

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.

 

Exactly this.
I would say 860* is very believable...actually lower than what I thought you were going to say.

 

860 is at the upper end of the normal temperature range at the standard 18" above the stove. Class A is rated for 1000 continuously. My auber probe meter doesn't even alarm until I go past 1000.

Then you are going from a very efficient, high mass, cat stove to a much less efficient lightweight noncat with a pretty direct path from firebox to flue and measuring right at the stove top. The super is a good noncat but much less efficient and so you can expect much higher flue temps.

Every time I burn my noncat NC30 I run flue temps up past 850 before starting to shut it down for a cruise. And that's measured up at 18".

 

Thanks everyone. It's reassuring no one thinks I'm about to burn the house down.

 

I was expecting you to say something much higher.