Originally Posted by Unfathomable Bastid
I have both a flat barrel lid and a weber kettle lid. I plan on drilling the hole for the thermometer in the flat lid (my weber kettle lid already has one). Unfortunately, my kettle lid doesn't fit the barrel tightly. It kinda balances on top of the rim, actually, even though the seal seems to be fairly good.
You probably won't see too much of a difference between the flat top and the cooking grate, maybe 20-25 degrees would be my guess, but try it and see what you get. I could be totally off.
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