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[litzerski]

So, after the last thread regarding foil vs no foil, I decided to take some time and gather real data.  This testing is to find if and what the temperature difference between the left, center and right sides of the cook surface.

First, I ran my Grid Iron at various temperatures (180, 225, 300, 375, 450) with foil on the drip tray and took actual cook-surface temperature readings using an Extech 42510a infrared thermometer.  I turned off the Grid Iron, let it cool down completely (under 50 degrees), vacuumed out the ash, cleaned the fire box, removed the foil from the drip tray and repeated the exercise.  Again, I took readings at 180, 225, 300, 375 and 450 degrees.  Between each temperature increase, I allowed 45 minutes for proper heat soak and temperature stabilization. 

Note that the foil used was 18" Reynolds Heavy Duty Aluminum Foil as available at Costco.  The heavy duty aluminum foil was carefully, tightly and evenly applied to the drip tray as a single sheet.  There were no tears in the foil and the drip tray had complete coverage.  The foil was wrapped up the sides of the drip tray and wrapped around the vertical edges.  The foil was wrapped down around the left and right ends of the drip tray and was terminated tightly against the inner side of the end.

Readings were taken mid-grate at the far left, dead center and far right sides of the cooker.  All readings were taken within 10 seconds of first opening the lid, which I can assume will reflect actual grate cooking temperature.  I considered taking center, front and back temps, but to simplify data points, I opted to strictly monitor the left to right temperature delta or ΔT. 

Ambient temperature was between 20 and 27 degrees during this testing.  Skies were clear with a light breeze (2-3mph) throughout the day. 

Cookin' Pellets Black Cherry pellets were used for testing.  Note that there was surprising little ash created during this exercise.  The Cookin' Pellets performed wonderfully and had no problems obtaining the temperatures required. 

For grins, I also monitored this test with a FLIR E6 thermal imager.  I first recorded an image of the rear of the Grid Iron, showing hot spots on the back of the unit, then recorded an image of the cook surface & drip tray.  While not completely thorough, I believe this helps paint a 3-dimensional picture of the hot spots inherent to this design. 

Before I get into the results, I must admit that I’m impressed at the affect foil has not on the ΔT, but on the overall temperature.  Foiling my drip tray made a clear difference on cooking grate temperatures throughout the temperature spectrum.  Also, note that I've calibrated my cooker (using the C-13 setting) using my Maverick ET-372 ambient probe with a foiled drip tray.  I will soon re-calibrate using a non-foiled drip tray.  The ambient probe was placed in the dead center of the cooker for this calibration.

Now for the results.  Please note that prior to testing, I only planned on capturing thermal images with the FLIR E6, not take individual temperature readings with the infrared thermometer.  I soon discovered that actual temperature readings would be more helpful.  My sincere apologies for this initial oversight which led to only a thermal image and no temperature readings for my first data set (foiled drip tray at 180 degrees). 

Here's my collected data.  Let me know if this should be bigger or smaller, I can change the size and repost.



In a following post, I'll post the thermal images.

[Bar-B-Lew]

Wow!  Interesting that the foil held the temps down so much compared to the controller temps.

So the big question is, are you going to continue to use foil going forward?

[litzerski]

No, I don't plan on using foil any longer.

[litzerski]

Also, I should mention, that though there has been some debate on the Godke Downdraft unit, I've ordered one up and will run temp testing with the Downdraft installed to see if it evens out temperatures across the cooker.

[rdsbucks]

As Mr. Spock would say, "Fascinating." Thanks for sharing. I had no thought that foil made any difference until now.

[pmillen]

I think that gathering data like this is another facet of Know Your Pit.  I like it.

I wonder about the advisability of testing an empty pit in this manner.  I don't know, but I wonder if butts or briskets would change any results.  It might be possible for you to simulate them by putting in a wad of damp towels.

A thought.

[Bentley]

So foil is a must when grilling?

[litzerski]

My question is do you think using a thermal infrared monitor versus an ambient probe may have distorted the temp readings?  I mean, I believe IR works off reflective heat, so maybe the foil's readings are due to its reflective characteristics versus the plain drip tray.  It would be interesting to repeat the test using the maverick to measure the cooking grill temps.

While I do think it may make a difference, for my main purpose of testing for ΔT, I don't believe it matters as long as the same foil with the same reflectivity lies directly under the cook surface I tested.  I debated using 3" x 3" pieces of 1/2" A36 steel directly resting on the grill grate (which I still may do) and measuring their temperatures to counter any other variables.  I'll have to think more about this though, as that adds more possible variables to testing.

Nonetheless, I believe I've accurately measured a pretty large temperature difference across the cook surface.  While I knew it was there from my initial biscuit testing, I had no idea it was that drastic (close to 100° at 450°). 

I'm more interested in getting the temperatures evened out than anything else at this point.

[bregent]

Makes sense, since the emmisivity of foil is so low, you'll get less radiant energy. I would think this will also effect the grill's RTD somewhat. I have thought about doing a biscuit test, with half the tray foiled and the other unfoiled, but never got around to it.

[glitchy]

I think the foil's emissivity may matter a lot:

https://blog.thermoworks.com/tips/infrared-thermometry/ (hope this link is OK since they help give back to the site too).

In there it talks about trying to read the infrared surface temp of boiling water in a shiny stainless pain and it may read closer to 100 degrees F than 212. While this is a great question as to what affect the foil on the drop pan may have on temps, I think putting much value into these results with IR readings is tough. Ideally, it appears from a little research, that IR readings are better on non-metallic surfaces period...so maybe small fireplace stones or something and also maybe probes as well to get a comparison.

Thanks for sparking the questions today...I never thought much about any of this until sschorr posted the question and had to know more about it. As for it mattering in regards to the delta? I think I'd measure with ambient probes after researching more.

[okie smokie]

My question is do you think using a thermal infrared monitor versus an ambient probe may have distorted the temp readings?  I mean, I believe IR works off reflective heat, so maybe the foil's readings are due to its reflective characteristics versus the plain drip tray.  It would be interesting to repeat the test using the maverick to measure the cooking grill temps.

While I do think it may make a difference, for my main purpose of testing for ΔT, I don't believe it matters as long as the same foil with the same reflectivity lies directly under the cook surface I tested.  I debated using 3" x 3" pieces of 1/2" A36 steel directly resting on the grill grate (which I still may do) and measuring their temperatures to counter any other variables.  I'll have to think more about this though, as that adds more possible variables to testing.

Nonetheless, I believe I've accurately measured a pretty large temperature difference across the cook surface.  While I knew it was there from my initial biscuit testing, I had no idea it was that drastic (close to 100° at 450°). 

I'm more interested in getting the temperatures evened out than anything else at this point.

I did similar testing some time ago on PH when I first got my Grand Slam.  There is considerable difference at the drip pan level with the Infrared, but the temps at the grate level were always achieved as set on the control.  I suspect that the bottom line is that it probably uses more pellets to get to  the set temp when there is foil on the drip pan. I did not test that at the time.  Other than economy, I see no cause to be concerned either way.  Is it not the temp at/on the grids that does the cook?

[Canadian John]

 1/ Colested data sheet size is perfect-by me.

2/ You  have spent a lot of time performing a most interesting test.

3/ Reminds me of visits to our engineering lab.

[litzerski]

Thanks for sparking the questions today...I never thought much about any of this until sschorr posted the question and had to know more about it. As for it mattering in regards to the delta? I think I'd measure with ambient probes after researching more.

Yes, I realize that my meager methods have their limitations, but tried to make do with what I have.  Next step is ambient temps across the cook surface.  I've been thinking about getting a Fireboard and this may push me over the edge.  I could get simultaneous real-time data for (6) ambient probes.  Maybe replicate this test with a pro-shelf and get multi-level data.

[bregent]

>Other than economy, I see no cause to be concerned either way.
>Is it not the temp at/on the grids that does the cook?

Yeah, but pellet grills cook by a combination of radiant energy, mostly coming off the drip tray, and convection from the moving air. If you reduce the radiant energy from below, it could theoretically alter the balance of heat and end up not cooking uniformly.  That's why I think a few biscuit tests would be interesting as you could see how it alters top/bottom browning.

[glitchy]

Thanks for sparking the questions today...I never thought much about any of this until sschorr posted the question and had to know more about it. As for it mattering in regards to the delta? I think I'd measure with ambient probes after researching more.

Yes, I realize that my meager methods have their limitations, but tried to make do with what I have.  Next step is ambient temps across the cook surface.  I've been thinking about getting a Fireboard and this may push me over the edge.  I could get simultaneous real-time data for (6) ambient probes.  Maybe replicate this test with a pro-shelf and get multi-level data.

I would have likely started the same way. I've used my IR temp gun a lot, especially on my Blackstone. I was thinking that unless you have objects on the grates, the IR could be picking up readings from the drip tray and not the grates themselves, it would be hard to get it that narrow, right??? I don't know, it's just a toy for me to play with at times. If it's catching the drip tray the left is going to be cooler and the right hotter on almost all the right side grease catching pits as the left is higher from the pot and the right is lower and closer to the burn pot to get more direct heat from the flames.

FYI, the Fireboard is really nice and if you have a charcoal grill/smoker or stick burner, you can get their fan controller and control temps on those too with the Fireboard. I like mine and still use it some with my Memphis even though it has it's own probes and WiFi.