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Q-talk *ON TOPIC ONLY* QUALITY ON TOPIC discussion of Backyard BBQ, grilling, Equipment and just outdoor cookin' in general, hints, tips, tricks & techniques, success, failures... but stay on topic. And watch for that hijacking.


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Unread 03-31-2008, 04:51 PM   #1
OSD
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Default UDS Heat Shield Experiment

I had the day to play around, so I thought I would see if a heat shield would help even out the temps in my barrel. First I calibrated the temp gauge that is mounted in the side of the drum and checked the probes too.
Probe #1 -- 211*
Probe #2 -- 211*
Probe #3 -- 213*
Temp gauge dialed in at 212*
Next I filled the small basket about 1/2 way and got a fire going and then put a grate on the bolts that I had mounted 10" above the charcoal basket. I set 2 probes in their holders on the cooking rack and brought the drum up to temp. I was surprised at the amount of temp difference from the side to the center. I brought it up to 200* on the outside gauge and the center probe read 263*. I held that temp for one hour then took another reading and it was 200* gauge and 254* center. So after awhile it settled in a little.
Now here's where no expense was spared for this experiment. I went to Wal-Mart and bought a 16" metal pizza pan. Cost $1.88 plus tax. It's thin metal but..........
I drilled 9 - 3/16" holes in it for drip holes.

I placed this on the bottom rack and put the probes back in place on the top rack. The temp spiked a little from having the top off, so I had to let it settle down for a while and level back off.
After running steady for about 30 min. it read 205* gauge - 217* center
So I raised the temp to 215* gauge - 232* center held that for 30 min.
Raised the temp again, 235* gauge - 251* center held that for 30 min.
Then I dropped it back to 215* gauge and just let it coast for about 2 hours. Surprisingly it only varied up or down about 3*-4* the whole time.




So, I'm guessing this may work. That pan was really thin. I'm wondering if a thicker piece of metal would also work better for evening out the heat?
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Unread 03-31-2008, 04:59 PM   #2
Kenny 13
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Hmmm, interesting. This might be something worth experimenting with.
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Unread 03-31-2008, 05:17 PM   #3
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Great experiment. I like the implimintation of the shield, but you may need to drill bigger drip-holes. I think the fat rendering-off a brisket or but may not flow too freely thru holes that size.
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Unread 03-31-2008, 05:22 PM   #4
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Quote:
Originally Posted by OSD View Post
I'm wondering if a thicker piece of metal would also work better for evening out the heat?
Another factor might be that the exhaust is in the center of the lid and perhaps drawing the heat toward middle of the drum as well.

Nice data on that pie-tin, though. Thanks for sharing.
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Unread 03-31-2008, 05:24 PM   #5
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Hmmmm....

Something to consider for sure. Hoping you do more research.
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Unread 03-31-2008, 05:32 PM   #6
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Quote:
Originally Posted by Thawley View Post
Another factor might be that the exhaust is in the center of the lid and perhaps drawing the heat toward middle of the drum as well.

Nice data on that pie-tin, though. Thanks for sharing.
I can vary the temp readings in mine by turning my kettle lid.
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Unread 03-31-2008, 05:37 PM   #7
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Quote:
Originally Posted by Thawley View Post
Another factor might be that the exhaust is in the center of the lid and perhaps drawing the heat toward middle of the drum as well.

Nice data on that pie-tin, though. Thanks for sharing.
That's a thought. Then, maybe a lid with exhaust holes evenly spaced around it could be the ticket toward drawing heat all around?
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Unread 03-31-2008, 05:41 PM   #8
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use 3/16" or thicker perforated metal sheet
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Unread 03-31-2008, 06:41 PM   #9
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Has anyone every tried a water pan for better heat distribution. I have thoughts of building 1 of these UDS' and either want to use a plate or water pan?
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Unread 03-31-2008, 06:46 PM   #10
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Everyone has good points. I agree the holes will have to be bigger, the metal thicker and the exhaust is part of it pulling the heat and always will be a little. I believe it would be easier to control with a kettle top instead of a flat top. More space above the cooking grate for the heat to go. I'm not saying it will or that I expect it to even out of all the difference in temps from side to center. but I have heard alot of people say they have 40*-50*-60* difference in temps, as do I. But what I did hope to accomplish out of this was to get the temp difference to a more manageable range of difference in temp. to maybe 10*-15* to make it a little easier for meat placement and timing of the cook.
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Unread 03-31-2008, 06:56 PM   #11
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Kenny, I think JD McGee has used a clay pan in his. I didn't want a pan in mine, I wanted to still have the drippings go to the fire for the added flavor it produces.
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Unread 03-31-2008, 07:14 PM   #12
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So OSD, how far above the basket was the diverter when you had the least amount of outside to center temp difference?
I could not tell from you description. It looks like you started with the diverter 10" above the basket and then moved it to the bottom rack which would be 24" above the charcoal grate. Sorry to be a bother just not sure. How about if all measurements are from the charcoal grate? That way we would be on the same page. People have different height baskets and have different heights for the grate from the drum bottom, so if everything is measured from the grate it might be easier see.

Good experiment.
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Unread 03-31-2008, 07:24 PM   #13
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I put in a 3rd set of bolts in to hold a grate. It is 6" below the bottom of 2nd grate. That would be 18" up from the charcoal grate. It stayed at that level the whole time.
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Unread 03-31-2008, 08:14 PM   #14
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Seems to me that a plow disk would make the ideal diverter. They are made of heavy heat holding steel.
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Unread 03-31-2008, 08:31 PM   #15
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Until I saw this post I've never really paid to much attention to the temps other than the pit gauge, but I was just out experimenting with 2 new drums of mine and my temps are not much different than yours. I just loaded up the baskets with 10lbs of Rancher (for experimental purposes only) and fired them off with the torch and let them stabilize with one plug open. One drum running at 230* with no food or grate, drum two running at 250* pit, with a grate and a perforated tray and Polder probe through a potato and an oven thermometer in the center running at 320*. Been that way for 2 hours and though not very scientific, when I've had food cooking and used the oven thermometer its never in the center of the grate but as close as possible, the temp difference is usually no more than 25*. Now I'm using Weber lids all the time and have noticed chickens cooked closest to the lid vent are cooking faster so I try to rotate the lid or meats. This is straight up direct heat, no baffle or pan.
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