Originally Posted by PhilipW
You shouldn't really have to give it more air after you take the lid off. In fact the opposite should be true.
If you think about it, before you take that lid off, you only have a very small amount of combustion air coming in through your intakes. When you take that lid off, the fire gets a huge gulp of combustion air (by comparison). It will burn through that air hotter than if you had not taken the lid off.
Your temp gauge drops only because there's some cool air in there at the moment, but the fire isn't running at that new cooler level, it's still hot as it was and even hotter now due to the extra air.
It will easily catch up on its own. In fact, I think most drums will actually run up in temp after taking the lid off. Many turn their intake air off before taking the lid off to prevent too much air from getting in and causing a temp spike.
You are correct, PhillipW. This is exactly what happens. I have built about 5 or more UDSs so far, with some different methods, and I can concur that the vent sizes and lid seals, and removal of the lid are major factors to the temp spikes and temp control.
I have set up a table with butcher board/paper on top. Whenever I tinker with my product (basting, temp-check, seasoning, etc) I always pull the rack out with the meat on it, and place the lid back in place. I get virtually no temp spike. Someone on here invented some cut-off vent, which is pretty cool, but taking the meat out, and putting the lid back on is a lot easier. The meat might cool slightly, but it is a non-factor when you are cooking something 12+ hours anyway like a brisket or pork butt.