Upper and lower vents, re: temp control

sdbelt

Ok, I've had my egg 24 hours now (purchased at BBQ's Galore in Scottsdale, AZ). I fired it up yesterday, and for my first attempt, made jerky. The first piece I pulled was awesome. The rest I managed to burn to a crisp, as suddenly 2 hrs passed before I got back to it. Stupid mistake.[p]Anyway, as I fire it up for the second straight day, I have a question I wasn't able to answer yesterday. Today, I purchased the the dual daisy-wheel, while yesterday I messed with the lid on sideways. So now I have seemingly infinite vent possibilities, so my question comes down to this: Of the two vent locations, upper and lower, which plays a more critical part in regulating temperature. Its appearing to me the lower vent does the most regulation, but I'm now struck with a strong wonder for how significant the upper vent plays a role. [p]Yesterday's attempt taught me little, and today, before I forget and burn another batch of jerky (I'm going on a backpacking trip this weekend, and I'd like to bring homeade jerky...otherwise a juicy steak would be in order), I'd like any input the list can offer.[p]Thanks in advance,[p]Steve.
New Large Egg Owner.

Nature Boy

sdbelt,
Sounds like you already learned a lot! The lower vent is much more critical. In fact, many of us cook without the daisy at all, and can maintain lower temps.[p]I am a huge backpacking fan. Jerky is killer on packing trips.
Welcome to the group! And have an awesome trip in nature.
NB

Char-Woody

sdbelt, for the most part, I agree with NatureBoy (Chris) regarding the use of the lower vent. This is your charcoal engine carburator. Higher and lower temps are its function along with a access to the used ash removal area.
But I have to disagree with my good friends in the use of the upper cast daisy and slider combo tops. [p]I find that it is almost impossible to maintain a fire of less than 250F degrees without a top dome cap in use. And the fire is less stable.[p]My reasoning for this and I think in using the BGE it will be born out is this. You have a 4 inch inner diameter circle top dome vent opening. If you do this, and I have done it, measure the temperatures to the edge of the dome castings, and then measure the temperatures directly in the very center of the dome. [p]Here is what you will find and it will amaze you as it did me.
There is about 60 to 80 degree's difference in the air ducting to the exterior wall vs directly down the center of the dome. The reason for this is hot air is escaping via the sides of the dome rising upward and out along the open top interior sides. At the same time, the colder outside air is ducting downward in a draft to the fire in the lower unit. Simple thermal technology..what goes out in volume must also come in as a proportional volume to its temperature, much like a jet engine functions.[p]By using only the lower vent for control you would find a minimum setting where beyond that you cease to have control. That is the primary reason I use both. I have a much better handle on the fire.[p]My head hurts.. this is more detail than you asked for but I felt it was time to vent me thoughts...:-)
Cheers to ya all...go ahead and disagree. It should be interesting. I am open to a better theory.
Char-Woody[p]

Tim M

sdbelt,[p]The answer is they both play an important part. Like NB said, many don't use them and as CW said, it's hard not to use one under 250 deg. [p]The fact is that they are best used together to compliment each other. Air expands many times as it heats up and the volume is increase as it enters the vent and moves up to the chimney. Since it expands many times, more volume comes out than goes in. Putting a restriction on the chimney will slow the exiting gasses and allow them to build up under the dome. This makes the Egg use less fuel to get to and hold at the cooking temp. I find the dasiy top is more for fine tuning a temp, but full open will give me 575-625 deg with a fully open vent -- perfect for pizza! The daisy open and the slide part closed will give you 350 deg approx, so the top helps getting to certain temps easily without the possability of going past them like what often happens with no top on.[p]Tim

sdbelt

All-[p]Thanks for the feedback. The dual daisy-wheel is definitely better than just the rain lid for these low temps. Over the last two cooks, I've had pretty good success keeping the temp right on 200. If the temp is falling below 200, its likely my fire is going out. If the temp is above 200, then my vents are open too far. Striking that balance takes some pretty fine adjusting of the vents. Tim M's picture of vents for 225 was very useful validation that I was on the right track. The second cook, with the daisy wheel, definitely made that balance easier to find.[p]Tonight I'm cooking something easy. Maybe a chicken or just burgers, or possibly steak.[p]Steve.

Spin

Char-Woody,[p]I have found the same as you, and agree with you. You can cook with either vent alone, but maximum controllable temperature range can only be attained by the use of both vents.[p]For higher temp cooks (475+°F) with a pizza stone (or firebrick setup), I like to use only the top vent to control the temp. It disrupts the airflow along the inside of the dome and evens out the entire internal dome temperature, especially the lower center area of the dome.[p]The best I can disagree ;-).[p]Spin

Char-Woody

Spin, thank you kind sir. The BGE is a fun mystery to work with. Understanding it results in its best rewards. I find that true in your results and postings also.
My best to Sue..she is a extra nice mystery too. Remind her that we have some hug debts to pay off.
Cheers...C~W[p]