Bottom vents and an even burn.....


 
M

Matt Sanders

TVWBB Pro
I've long wondered if it's necessary to keep the bottom vents on more or less the same "setting" to get the charcoal to burn evenly. For instance, (assuming a calm day) would the fire burn differently having one vent 100% open and the two others closed, as opposed to keeping all 3 vents 1/3 open?

I've generally kept the vents the same, unless one side of the bowl seemed much hotter than the other parts, in which case, I closed that vent a little more.

Any thoughts? If I can't get science, I'll take anecdotes...
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I don't hesitate to have them unevenly open. (Oxygen's oxygen, right?
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) For me, it's a couple factors: Desired cook temperature and wind direction.
 
Monty.

Right. But I wonder if the part of the fire closest to the vent burns most of the oxygen before it can get to the other parts of the fire, and thus, a hotter fire closer to the open vent, and cooler fire closer to the closed vents.
 
Once oxygen is used in combustion, it goes off as part of another compound (CO or CO2, for example), making it unavailable for use. So it stands to reason that the area of fire that is closer to the oxygen source would burn hotter than the area of fire that is away from it.

My guess, though is that the difference is fairly negligible, at least for the purposes of running it in a WSM, where a deflector is presumably in place, and the meat is far enough away from the fuel source, that it all just contributes to ambient heat in the environment. Of course, there will always be hot spots and cool spots, but you'll likely have that even if you keep all your vents uniformly open.
 
Here's your anecdotal, and this is one of those things my old one-intake UDS taught me. However, I admit that I must have forgotten until recently when I asked about issues with ATC's and uneven burns.

Basically, before I even knew anything about ATC's really, I learned that a fan would stabilize the draft on my old ONE-intake UDS in windy conditions. It was a bit touchy and I'd have to play with the angle and all, but I was cooking faster and not overnight. So since I don't use a fan and the wind is a constant variable...that's why I prefer setting the vents equal.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">My guess, though is that the difference is fairly negligible, at least for the purposes of running it in a WSM, where a deflector is presumably in place, and the meat is far enough away from the fuel source, that it all just contributes to ambient heat in the environment. </div></BLOCKQUOTE>

Sean,

I was thinking the same thing from a cooking perspective, it probably doesn't matter much (with the exception, perhaps, of a high heat cook if part of the meat is outside the circumference of the bowl). However, I wonder if a badly uneven burn might leave a lot of fuel unspent in part of the ring, or some woodchunks unburned. So while it probably has little direct impact on the temps in the top chamber, it might affect fuel endurance and wood chunk burning.
 
Had to take a call, but my post above was to point out that there's a difference between a fan or ATC BLOWING into the only intake vs. only one intake being open that's sucking air and dealing with shifting wind.

Sean's right, though. The charcoal will generally burn quicker by the door and the vent that's most open. On a related note, uneven burns is part of the reason I don't use the coffee can method, lighting just in the middle. I prefer to light the ring in the middle and in three spots between the vents, whether with a torch or four firestarter cubes.

Anyway, uneven burns aren't really a big deal, at least if you keep a fair amount of water in the pan and keep the meat over it. I used to try to smoke lots of leg quarters with a foiled pan at higher temps and the chicken would all be done at various times. With water in the pan cooking low-n-slow I often can pull everything off at once, believe it or not.
 
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">So since I don't use a fan and the wind is a constant variable...that's why I prefer setting the vents equal. </div></BLOCKQUOTE>
Ditto. In the absence of a windbreak, if there is wind, I might close the windward vent more. All things be equal however, I use even settings. I do not care for the uneven burns that result from single-vent-control or the like.
 
I don't know if it's due to warmer climate here but I normally have to smoke with 2 vents almost totally closed and just adjust one.

I have noticed that it seems to help the amount of smoke I generate with a chunk of hickory wood for instance if I position it in the coals closest to the most open bottom vent opposite of the top vent.
 
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