Pit Probe Placement

tofof edited this page Apr 24, 2018 · 3 revisions
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The question often comes up where to place the Pit or Control probe in order to have the absolute best accuracy and make award-winning BBQ in a charcoal smoker with perfectly even temperatures within 1 degree of the setpoint. In my experiments and 7 years of HeaterMeter development, I can tell it almost doesn't matter and any attempt to control the temperature of such a random environment is a fool's errand.

Even in a solid ceramic Big Green Egg with the ceramic heat diffusion disk, there are hot spots that later can become cold spots. Temperatures at grate level are different than at dome level, and not in a consistent manner-- one may start hotter and become colder than the other and vice versa. To help quantify what we're dealing with, I've included the results of my last heat zone experiment here.

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. 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.

ProbePlacement

  • 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.
  • Near - 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".

Graph

There's a lot of churn here over 6 hours. Clearly the gray probe ("Near") 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. 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.

         Avg      Error from Center
Dome -   249.2    -7
Center - 256.2    0
Far -    262.0    5.8
Near -  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 piece of shit 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 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. Unless you've arranged the majority of the meat to be exposed to those heat currents in which case this would be the ideal place to put your thermometer, which you couldn't because the meat is there!

I personally use a thermocouple clipped to the end of the built-in dome thermometer. This may be a little cooler than the our ideal positioning at center-grate level, but its location allows it to average out the overall temperature at the grill level and provide a somewhat consistent place to measure temperatures. If your measurements are consistent, then you can adjust the setpoint temperature to meet your meat needs and overall produce a consistent BBQ output.