Does it matter where the PIT probe is placed? Not really.


 
Bryan Mayland

Bryan Mayland

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I needed to do some other testing so I thought it would be fun to illustrate how probe placement is a little important, but dome vs grill level doesn't matter in a ceramic cooker. Behold the test setup! 3 probes at grill level, run through wooden clothespins and held roughly an inch above the grill at different locations. 3lbs of lump charcoal were loaded into a freshly cleaned Large Big Green Egg and lit with a weber starter cube. All probes have undergone a 1000+ point calibration to be within 1F of each other.


  • Center - A probe located centrally over the big green egg ceramic disk (or is it a disc?). This probably would be the A#1 duke of positions to place your control thermometer it weren't taken up by all the inconsiderate meat we're trying to cook. We'll use this probe as our reference we're trying to track.
  • Far - This probe is located off to the side, but with the last 3" of probe shielded by the ceramic. This is a typical location a probe would be placed if the grill had food on it.
  • Close - This probe is also off to the side but you dumbass, the tip is in the draft of the fire. This probe experiences most of the unshielded heat of the fire and is where the "Far" probe might end up if things get knocked around
  • Dome - The orange line is a bare thermocouple in the dome, which I am claiming to be "just as good as at grill level".


There's a lot of churn here over 6 hours. Clearly the gray probe ("Close") is never in a good position to asses the temperature compared to the light green ("Center" ) probe. The dark green ("Far") probe is closer, sometimes following the Center probe, but sometimes moving in the opposite direction with temperature differences exceeding to 20F. EDIT: The big dip down in the middle is where I opened the lid to take a picture of the probes.

Let's compare average temperatures starting at the first time the orange probe passes the red setpoint line.
Code: 
         Avg      Error from Center
Dome -   249.2    -7
Center - 256.2    0
Far -    262.0    5.8
Close -  280.4    24.2

Given that we can't place our thermometer right in the middle of the grill, the dome temperature is 1.2F difference from being at grill level. 1.2F over 6 hours is virtually the same, especially considering the probes are only calibrated within 1F of each other. The dome temperature has less maximum deviation from the center location too. As a caveat, "Dome" is not the dome thermometer. That thing is a bimetalic piece of **** and read anywhere from 240F to 290F through the course of testing despite being literally attached to the thermocouple.

In conclusion, I assert that you do not need to measure your BBQ temperature at grill level. If you can get it situated centrally, that's probably the best. However, a shielded position at grill level or a thermometer located in the dome, with only a 6 degree difference in either place, roughly equivalent. A probe tip which is exposed in heat currents is definitely a bad idea.
 
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I used to run my 7" TC pit probe through my dome vent just because it is easy. Then I moved to a clip that holds the same pit probe about an inch above the grill grate. I actually noticed a fair difference, the food is cooking faster and coming out of the grill hotter with the pit probe at grill grate level. Your graph seems to show a 10-15F difference between the orange pit probe line and the grill level probes unless I am reading it wrong? That tracks pretty close to my experience when moving from the dome to the grill grate with the pit probe.... that is to say, about 5% faster and 5% hotter....
 
That definitely depends on the smoker

My UDS can be as much as 50° difference from center, from side of the grill to even 8 inches from below or above the grill. I always take grill temperature from one inch below center of grill.

I think being a ceramic smoker the temperature is more even throughout the smoker.
 
RalphTrimble said:
Your graph seems to show a 10-15F difference between the orange pit probe line and the grill level probes unless I am reading it wrong?
Click to expand...
There's a 7 degree difference between the dome and grill level, or a ~6 degree difference between two places at grill level. Sometimes the dome is hotter, sometimes it is cooler than the ideal point. In this test the average grill center temp was above, but I've seen it be closer or below dome. I would agree that it is most commonly warmer at grill level, but not significantly. I don't think you can really reliably measure "5% longer" when it comes to a 12-14 hour smoke of a hunk of meat especially given the variation of temperatures at the grill level. One side of a pork butt could be 20 degrees hotter than the other!

And John is right, these findings are specifically for ceramic cookers. It probably makes a whole heap of difference for UDS or WSMs.
 
If there is an average 10F difference between the dome and the pit probe some simple math tells you the story, 10/225 X 100 = 4.4% difference when cooking at 225F...
I've done enough cooking on my "fauxmado" to know the grill grate area is running hotter, or closer to the actual setpoint, when then pit probe is at grate level. I KNOW the food is cooking faster, the bones poke out of my racks of ribs quicker, and I know the food is cooking at a higher temperature because it is hotter when it comes off the grill. This stuff you just know after two years cooking the same foods on the same grill.
 
I appreciate this testing Bryan. I have been thinking about running my thermocouple probe to the BGE's built in thermometer, just alligator clipping it to the tip, and leaving it there permanently. I've definitely known that leaving the probe temp in the draft of the fire can cause temp readings to be off. But I get tired of trying to find a place on my grill that is shielded by the plate setter and yet still away from the meat.

Anyway, I think this test convinces me that I'm safe doing that in my ceramic Big Green Egg. Which is good, because my new thermoworks probe gets in today.
 
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