Dome temp vs Pit Temp

[inacoma]

All,

throughout the years many have stated Dome (or normal top temp probe on non-dome grills) as the way to read temps...i.e. low and slow between 200-250 for pork butt. Well, my question is this.

I use a Stoker and when it shows the pit temp (the temp at the grate) at 250 degrees, my dome temp shows around 310-325 degrees...

So based on old lore...you would think you are cooking too high? but based on pit temp, you are right where you need to be?

Which is the correct way?

ktp

[Firemonkey]

That seems like a big difference in temps. Where are you placing the pit probe?

I dont have a stoker, but I recall checking the difference in the temps when my KK was still new. I think the difference was only like 10-20 degrees from the main grate to the dome (dome hotter). I also sometimes place a wireless thermometer near the meat to monitor grill temps until things get close to finished, then I put it in the food. I have not seen that much difference between the grate and the dome.

[johnnyboy]

I have the same question; where is your pit temp probe?

If your dome thermo is reading 310+, and your pit probe is reading 250 I'd say maybe your pit probe is placed too close to the meat, potentially picking up the meat temp.

[jdbower]

I think the best answer is "whatever works for you". IMO the pit temperature isn't all that important in absolute terms, it's how the meat comes out that matters. As long as you're consistent in your measurements you should be mostly consistent in the outcome, so if you find a combination of pit and/or dome temps that work for you I wouldn't sweat which one is more accurate. A few thoughts:

What you're seeing is close to what I see, my pit temp is usually lower than my dome temp when cooking indirect but I don't think the change is as dramatic as yours, I'll have to pay more attention next time but I'd guess that it's closer to FM's 10-20 degrees.

The closer your pit probe is to the meat the colder it will read. This will have an interesting effect of gradually decreasing the temperature over the life of the cook as the meat gets hotter.

Conversely, if you put the pit probe too far away from the meat you may catch the thermals coming around the heat deflector and it'll read too hot.

You may also want to calibrate both thermometers if you haven't done so. I calibrated my dome thermometer in boiling water before I used it (but haven't checked to see if it's still OK after being in subfreezing weather much of the time). I never bothered to check my Stoker probes for accuracy, but my end results have been fine so even if they're off it doesn't bother me.

BBQ Guru sells a probe tree that can hold multiple pit probes. This could be an interesting way to check the temperature at various levels in the grill but I don't know how the Stoker reacts to multiple pit probes tied to the same blower.

[Conodo12]

Hmmmm... Sounds like it may be time for a calibration. However, before doing so, find out which temperature device is closest to being accurate. I grabbed a thermometer from my kitchen drawer that was older but uses good ol' mercury to reflect the temp. I brought a small pot of water (about 5 inches deep) to a rolling boil and proceeded to checking my Tel-Tru and Guru against the mercury thermometer. As we all know, water boils at 212 degrees Fahrenheit at normal atmospheric pressure. My mercury thermometer read closer to 214 but why split hairs. I know it was close. [*Important* - when checking the temperature of the boiling water, you must use a pan clip or rig something so that the temp probe is in the water but not touching any of the sides or bottom of the pan.] My results showed that my Guru was damn close to spot on. My Tel-Tru was just a bit high but turning the calibration nut got it perfect. To test out my newly calibrated toys, I inserted my Tel-Tru where it belongs on my KK. I then clipped my guru pit probe to the Tel-Tru probe about half-way up the post. There is an indention on the Tel-Tru about 1 3/4" from the tip of the probe. The folks at Tel-Tru tell me that portion of the probe is used to check the temp. So, at the end of my experiment my Tel-Tru and Guru now come in within a few degrees of one another and often times reflect the same temp when reading temps at the same location. The difference between the Main grate temp and the Dome temp is about 7 to 10 degrees give or take. It is not a difference of 50 to 75 degrees as you are finding. Also, I think it is important to note that when I did a comparison of the temps between the grate temp and the dome I did NOT have a heat deflector installed. Also, my temps were rock-solid for at least an hour before I started taking measurements.

I hope this helps! Just for kicks, I'll take a new measurement this weekend as my last calibration was in November.

One last note - when I had my Stumps Smoker, which is a large cabinet style indirect smoker, we were advised to bake some rolls on each shelf to get an idea of the difference in temps between the bottom and top shelves. There were 5 shelves in my unit so I baked a-lot of rolls. This little experiment also helped to locate "hot spots" in the cooker. It would be interesting to cook up some rolls on the main grate and on the upper-grill to determine just how much faster the rolls on the top level baked if at all... On the Stumps, the bottom shelf cooked the fastest (closest to the heat) and the top shelf was slower. However, even though there was about 48 inches difference from the bottom to the top, the temp sway was not very much. I suspect the temp difference in the KK would be less due to the close proximity of the two shelves. So go bake some rolls and find out!

[inacoma]

Wow!! Thanks for all the replies!! I'll try to address them here:

Yes, the probe's are calibrated (had to calibrate at 6k ft...as I live in the Greater Denver Area...thus our boiling, on day of calibration, was 201 degrees IIRC

The pit probe is actually very close to the butt, I would say about 1 to 2 inches. I'm guessing that's why the temp is reading very low there. I also have the large pizza stone over the coals AND a stainless drip pan on the lower grate (butt is on the top grate).

...I just checked...my dome temp is at 280 and my probe temp is at 245...I'm 35 derees off!!! rather than open the KK I'll just adjust my pit temp down about 15-20 degrees or so degrees (some had said thy only had a 10 to 15 degree variance between pit and dome)...

...thanks!

Kumar

[johnnyboy]

If doing a long low and slow, and your pit probe is only an inch from the meat, I'd suggest using your dome temp versus pit temp.

[GregR]

I, too, have seen large differences between the dome temp and grate-level pit probe on low and slow cooks, early in the cook. The temps seem to converge as the cook progresses, suggesting that the proximity of the pit probe to the cold meat is the issue.

[inacoma]

So what sort of distance are we looking at here?

if the probe is on the outer rim of the grate, it could be reading too high since the deflector deflects all the heat that way...if too close to the meet (center of grate), then it's too cold. I guess split the difference?

ktp

[jdbower]

I'm guessing there's some interesting postdoc work in thermodynamics if you want to find the ideal location, but splitting the difference sounds good to me. If you've got an oblong meat shape I'd also put the probe along the long edge - this will give you more space between the side of the meat and the side of the cooker.

[Jim Malter]

I find that as the KK heat soaks (1 hour or so after lighting the charcoal), the temps at the grill and the dome get very close. I place the Guru probe at least an 1" from the meat but try to make sure it is also not in direct heat (i.e. the deflector is between the fire and the probe). Having said this, if the product is to your liking, the temps don't matter much.

Jim

[ThreeDJ16]

Guru suggests placing you pit probe at least 2" from the meat.

http://www.thebbqguru.com/bbqGuruU.cfm# ... ePlacement

Also, thermal saturation of the ceramic plays a big part in your dome temp to grate temp differences. If you let your grill get up to temps an hour before you placed on your meat, there would probably be less of a difference. But then again, who cares as your wasting charcoal.

I always try to get the probe somewhere above the deflector and 2" from the meat. That seems to be about the best representation you can get. Pick one temp location or the other and when your happy with it, just stick to it for consistency.

-=Jasen=-

[ThreeDJ16]

Opps, forgot to add this. Sounds to me like the pit probe being to close was your culprit. As everyone stated, this makes the pit temp read low. But this also means your fire burns hotter trying to make the pit temp read the correct value. Which in turn, the dome temp will read a much higher value. That would also explain your higher than average temp differential between the two locations. Anyway, no worries, easy fix!

-=Jasen=-

[Syzygies]

This is all relative, because one learns to cook based on a given instrumentation strategy, as long as one is consistent. The debate whether to do a low & slow at 210 F or 225 F gets mixed up with this debate; no two people can accurately compare these numbers or their probe locations, but one person can learn through consistency how to obtain the barbecue that they like.

I reason that with the probe 2" from the meat, I'm measuring the boundary effect that directly determines how the meat will cook. If there are other lags in the system (there are!) then they're not distracting me, e.g. I'm not waiting for the dome temp to equalize with my grill measurement before I get "full traction" from the control process.

In other words, I don't see what advantage I gain from the grill temp around the meat starting out lower than a dome temp held steady by a guru. If I want a lower starting temp, I could just dial this in manually.

On the other hand, having made the decision that I'd rather regulate the temp 2" from the meat, I regulate it as a lower temperature than I would have selected for a dome temp.

To summarize, I want to control the temp where it matters most, then compensate for how this could be a different number than I'd choose for a different location.