So I've been doing a lot of mod research here, and while I'm not trying to refute proven methods, I'm still trying to understand the logic behind extending the smokestack into the cooking chamber. As I found in my first failed smoking experiment, excessive smoke is the enemy. Just to make sure I'm correct in my assumptions I'm just going to list out my observations. Please feel free to correct/educate me if you feel differently.
1. Creosote is about the nastiest thing you can eat, and should be avoided at all costs.
2. Creosote is caused by excessive smoke in the cooking chamber
3. Extending the smokestack into the cooking chamber interrupts the flow of air, trapping more air/smoke in the cooking chamber.
It just seems to me that by extending the smokestack, you're trapping all that smoke in the chamber for longer periods of time, and promoting creosote buildup. Obviously, I must be missing some benefit, or reasoning behind this, but I cant see what it is. Thoughts?
To answer your question pertaining to stack extensions (on horizontal sfb smokers), it provides a means for better control of the smoke chamber gas flows. It allows for better flow of gases closer to the cooking grate which can in turn allow more evenly heated smoke chamber space. Without a stack extension, the gases will more readily travel directly to the upper most point in the smoke chamber and this condition can result in widely varied temperatures between the sfb end and vent end of the smoke chamber.
Creosote can be caused by a few things including use of unseasoned (green) or coniferous smoke wood, as well as stale or excessive smoke in the chamber of your smoker.
While the methods for avoiding the first two are obvious, the last two may not be. A few causes which come to mind are using the vent damper to control chamber temps, which should be accomplished with the intake draft control, instead. Another cause would be using too much smoke wood or the smoke wood being exposed to too much heat/air in the fire box.
What we refer to as thin blue smoke is the sweet spot we try to achieve. You will notice that when wood first begins to smoke, it will give off a white smoke. That is caused by water vapor and some volitiles contained in the wood which are released when it begins heating. This is normal and expected when you add smoke wood, etc. To get the thin blue smoke we want to have, you must balance the amount of heat and air which the smoke wood is exposed to. More heat/air will result in a faster, heavier and shorter lived smoke.
Ultimately, if you can smell smoke exiting your chamber vent, or if stings your eyes if you put your face in the path of the vented gases, your smoking. Less is more, IMHO. You can smoke your foods for the entire time they are in the smoker, but this is really not necessary. The longer it is exposed to smoke, the heavier the flavor, but going overboard is very tempting.
EDIT: You will find that the smoke flavor of your foods may not seem very strong to you, as you have been exposed to it numerous times during a long smoke of brisket, pork butt or a turkey, as examples. The causes for this are that your sensory perception of the smoke will be deadened somewhat from the constant exposure to the aromas of smoke. It's in your hair, the fabrics of your clothing and on all your exposed skin. So, you carry it with you everywhere throughout the day and into the night (or vice versa) on a long smoke, until you remove your clothing and get a fresh shower. The day of the smoke, your food will not taste like it has much smoke flavor to you, but to those not exposed to the smoke as you have been will feel differently on the subject. The day after, it will taste just fine, as your normal sensory perceptions will have somewhat recovered by then. Taste and smell will have returned to normal.
One last note: whether you use a smoke box/pan or some type of container for the smoke wood, there should be a black/charred piece left over from your smoke wood after several hours. If ashes are present, the wood began burning at some point during the smoke...you want to avoid this condition.
Hope this explains things better for you.
Enjoy you addiction to smoked foods!
Eric