I built a Walker style bbq and have a few questions. I built a 6x6 core and thoroughly dried it out with a few burns before putting the barrel on and cobbing it up. The core draws pretty well and I get a decent, though not spectacular rocket sound.
After adding the barrel, cobbing it in and adding a chimney, the sound is gone, the draw is lazy and fire creep and smoke back are the norm. Not good. Also, the temp in the grill only got to 350*, well below what I had hoped, and I can hold my hand comfortably above the 5' chimney indefinitely.
I think I have several issues to address.
1. Wet cob. Even though the core is dried and fired, is it really possible that wet cob downstream can slow the stream enough to kill the draft, and the thing will improve as it dries?
2. My top gap is 4" due to a miscalculation. I could add an extension to the riser, but will try other things first.
3. Chimney too small. I think this is most of my problem. I'm using a 4" chimney for a 6" system. I assumed that with the hole in the barrel top to allow gases into the grill, and the heat shedding off the barrel sides that I would need a smaller chimney to compensate and keep the velocity up. I should have done the math first.
A 6" system with a 3" bbq hole leaves 27 sq" to exhaust. The square root of 27 / 3.14 is just over 5" (not 4" - doh!).
Since I'm using Matt's adjustable top damper idea to control grill temps, my question is should I go to a 5" or 6" chimney. Or specifically, is there any downside to using a slightly larger chimney, say 6" when a 5" will do the job in most cases? I suspect not and presume larger is the better of the two options since that will allow proper venting when the damper is mostly closed, but thought I'd ask to see if anyone has thoughts.