Smoke stack?

[FastFreddie]

Is it better to have the stack closer to the grate or traditional style? Please tell me the pros and cons of both. All opinions are welcome. Thanks

[Mo Smoke]

Bro..I haven't finished my first one yet. But I asked about this too a few months back. (Correct me if I'm wrong boys) but what I got out of it was that there is not a better or worse. Just a matter of preference. Two reasons to run the stack down into the chamber.

1. To get the stack closer to the cook shelf, with the objective of keeping the smoke moving acrosss the surface of the meat. You don't want too much smoke and you don't want stale or stagnant smoke. Since the smoke is drawn by the stack, the theory is that the smoke stack will pull the smoke down to its level which would be the same level as meat sitting on the cook shelf. Smoke then exits out of the chamber.

2. To lessen the distance the smoke stack sticks out of the chamber. Could be for aesthetics or could be because of height clearance issues in the areas where your grill will be operated or stored.

I'm a rook, but I've been picking these guys brains for awhile now. One thing is for sure, you've come to the right place. These boys will take you to school. Good luck with your build, and welcome.

[Rev.Mike]

have built a couple both ways. and really didnt notice any difference, my thoughts would be that it can cause turbulance, and possible stale smoke at grate level, FWIW

[DUAYNE B]

I build all of my cookers with the stack flush with the top, nothing sticking inside the cook chamber. If you have your calculations correct,,,,,,, intake opening and stack length and diameter, the heat will pull the smoke through the cookchamber and there wont be any stale smoke. I figure it gives me more room for meat also.....but intake and exhaust are the important parts

[FastFreddie]

My first thought is always stale smoke. But what if I put a little half inch tube that runs from the top of my CC to my stack to help evacuate the smoke that will be stuck in the top. Sorry my brain is just clicking out random thoughts

[DUAYNE B]

I have yet to turn out nasty stale smoke Q. The info I got and get from this site helps make a well tuned pit .... the Pit Calculations being correct is the key, if the stack is too small, the intake not correct, or even the position of where the intake is. I had to totally redesign a fb door after it was all completed. I did the test burn to see how it was going to all react and found that just having the intake in the door a bit higher then the last couple builds, kept the fire from burning clean,,,,, I think where people come up with stale smoke is when they dont have a finely tuned cooker....... just my experiences talking lol.

[Rev.Mike]

[FastFreddie]

Thanks guys. I am now going to just build it regular.

[SoloQue]

I think where people come up with stale smoke is when they dont have a finely tuned cooker

I run dual stacks mounted on the outside equal to just above the lower rack but all the diminsions and ratios are straight from the calculator. The only time I have ever experienced "stale smoke" was when I overloaded my FB and then cut back too far on the intakes in an attempt to grab some extra sleep between fueling on an overnight cook. I starved the fire and ended up with smoldering wood that was not completely igniting and yes that was some crappy Que when all was said and done. To answer your question you first hand could find a a buddy with a set up with a flush top exhaust and insert a piece of rolled up gutter flashing that will extend down to the lower grate. After taking some readings during a test run remove the extension and take some more readings without changing anything else. The exhaust location should not effect airflow but rather overall potential temp zones inside the cooker. You may find that one design results in temp zones you prefer over the other. Only thing I would say is when you pull out the inside extension you put it back as an extension on the outside so that the overall exhaust length is equal during the whole test process just. If yo ugive this a try post some results and we can put this one to bed.

[Big Steve]

I'm trying to reduce temp zones across our cook surface. The CC is 60 wide. Cooking grate is 48". I've got two Tru-Tel therms mounted 2" above the bottom grill. Without closing the exhaust damper back 75% I have a 50+ degree difference between the two therms. At 75% closed I can get the temp difference down to 20-25 degrees. Monday we tested by extending the stack down into the cook chamber down to the lower grill. I though for sure that would cure the temp difference. I was wrong. Once again I'm back to throttling the exhaust damper to reduce the delta. Any tips?

[Mo Smoke]

I don't have an answer for you bro, but I do have a couple of questions for you. First, did you calibrate the thermometers? I read that some of them may need this to be sure to get accurate results. Second, which side reads the hottest? I assume the side closest to the smoke stack and firebox. Most guys say leave the smoke stack damper wide open and use the firebox inlets to make adjustments. Are you using both to control temps? Is it possible that you are just doing too much and not waiting to see the results of each adjustment? Frank says it takes about 30 mins to see changes after you make an adjustment.

[Puff]

I may be missing something. Are you able to control the fire using the dampers on the firebox? I know with my RF smoker, 85% of my heat management is from the FB dampers! I have not yet had to close the exhaust damper much at all. FYI...not that I am any seasoned cooking pro but I have had 1 turkey, 1 rack of ribs, 2 chickens and 30 racks of ribs at different times...2 extremes!.

[Smokeone]

Either of those could be an issue. At what point in the burn do you see the huge diff? Is it constant? If so you may try a deflector plate at the firebox opening. Or maybe try moving your fire around in your basket, or moving the basket as far as you can from the opening in the chamber. This may take some of the direct heat off of the BP, and allow the temps to be more stable.

Clear as mud?

[Big T]

Have you tried pitching the nose up or down just a little, I have to run mine with the nose about 1/4''-1/2'' higher than my FB.

[Rev.Mike]

[Big Steve]

Today cook (2 pork buts, 5 racks of ribs, 16 chicken thighs and some brats) was another head scratcher for me. I control the cook chamber temp with the firebox inlet vents. The exhaust stack is pinched back to reduce the mass gas flow across the cooking surface. When closed 75% I can get both therms within the previously stated 20 degrees or so. When I open the stack cap 100% (after having a stable fire and temps for hours) the therm nearest the firebox / stack side climbs in temp right away and the right therm (end of the BP) the temps dives. This happens in the course of several minutes. I'll see a huge 50-70 degree difference in temps from each side. As soon as I close the exhaust stack 75% the opposite pattern happens and I get the temps within the 20 degree spread. During all this time the inlet firebox vents are left alone. It's a strange thing. With it pinched we do not have stale smoke condition. I've raised and lowered the nose to no avail. I've moved the firebasket around and found that it helps a little but not much, unless of course it's over stuffed, which I avoid when I'm tending fire. I guess it's not a bad thing to have a slightly cooler cooking zone, but at this point I'm on a mission. Today we installed an upper cooking rack which runs hotter than the lower cooking surface. This I actually liked as I could get crispy chicken skin and still be doing a medium low and slow cook on the lower rack. The Feastie Boy is a finicky beast. Each cook brings new challenges and new learning. I much like it because I keep coming back for more.

[Mo Smoke]

What about adjusting the FB inlets instead of the stack damper? I dont know how many you have or where they are located on your firebox but its worth a try. Leave the stack wide open and see how working the temps from the other end affects the outcome. I read a post here that said " look at it like the firebox inlets are for major adjustments and the stack damper is for fine tuning.

[Big Steve]

Thought I was clear that I do my temp control adjustments with firebox inlet vents. If that wasn't understood, that's on me. I build a fire and let it burn, close the inlet vents to about 1.5 to 2" open on each side and let the pit settle for 30 minutes. At that point I have a huge temp difference between firebox side and BP side. I then close the exhause stack 75% and that temp difference reduces. The hot side temp falls and the cold side temp rises. When it settles out in 5 minutes they are about 20 degrees apart. The role the exhaust adjust provides, at least to me, is it slows the mass gas flow or draft down. With wide open it drafts so hard that the hot air on the BP side gets turbulent and hits the top of the grill and rolls down the cook chamber till it hits the exhaust. Is this a unique problem with my smoker or have you guys had similar issues. At this point I'm digging out the plans to verify we built right or perhaps maybe I cut twice and only measured once. Yikes.

[Mo Smoke]

My bad bro...I read your last post again and you did say that you control your temps with the FB inlets. I just missed it. The last thing I can think to ask is have you tried building a smaller fire? Check this thread.

Temperature Variation in RF Smoker
viewtopic.php?f=11&t=1505

Quick question for you.. How much difference are your temps from top to bottom? Mine won't be quite as long as yours so I hope left to right temps won't be that big a deal, but Since I have 3 racks roughly 5-6 inches apart, I wonder about the difference from rack to rack.

[SoloQue]

I have experienced most of what you are describing. For me it was a series of 4 adjustments. 1) I now make sure I have my charcoal basket centered and not all the way back in the FB, I'm going to contribute this to too much direct heat slamming against the FB end of the cook chamber. 2) I laid in a heat sink type shelf under the cooking rack on the FB end of the cook chamber. That shelf extends about 1/3 into the main CC. It is nothing more than a heavy piece of metal on small feet that reduces radiant heat from the heat baffle. 3) I bought a welding blanket and had my wife make a nose cap which greatly helped evenout the field since I have zero wind leeching the BTU's from the front 1/4 of my CC 4) I found that my smoker likes to be brought up past actual target temp with full exhaust stacks open and then with the exhaust stacks 25% closed it eases back down into my target temp range. During the full burn / full exhaust heat up I used to see as much as 75 - 100F F difference from left to right but now that I have made these tweeks Pops will run about 10 - 15F left to right when I follow this process ... Inhibit the radiant heat near the FB, reduce the lost BTU's around the nose and reduce overall airflow throuth the CC. If I want some variable zones I take off the nose cap and open the stacks. I can then do chicken in the upper nose, ribs on top near the FB, a butt down low near the FB and warm sides in the lower nose.

Hope this helps

[bluecatfish]

Have you checked the stack dimensions with the pit calculator again in case there was a miscalculation in size originally causing to much draft? Just a thought.

[Big Steve]

My bad bro...I read your last post again and you did say that you control your temps with the FB inlets. I just missed it. The last thing I can think to ask is have you tried building a smaller fire? Check this thread.

Temperature Variation in RF Smoker
viewtopic.php?f=11&t=1505

Quick question for you.. How much difference are your temps from top to bottom? Mine won't be quite as long as yours so I hope left to right temps won't be that big a deal, but Since I have 3 racks roughly 5-6 inches apart, I wonder about the difference from rack to rack.

Glad to see I'm not the only guy to speed read posts. I also have the problem of speed typing. The words are right in my head but I omit typing the word or use the wrong word. Kind of like bad spell check. lol.

Yes, I've learned over time that a smaller fire is better than a larger fire. Smaller means easier to control, only down side is feeding the beast at a higher rate.

[Big Steve]

Hey SoloQue, this is for you. I also installed a second BP (with a air gap) from the firebox end down about 1/3 the way down the cooling grate. It did help, but not to the degree I thought it would. Similar minds.
As you mentioned you see the same temp deltas and use the exhaust to slow or reduce the overall air flow through the cook chamber. One thing I've thought of today is to weld up a piece of 1/4 plate about 6" wide to the BP end of the cook chamber and place it between the bottom cooking rack and the top cooking rake. What I'm envisioning is the hot air flow gets to the end of the BP and climbs up to the top of the chamber then runs down the chamber and into the exhaust via the draft it's pulling. We did install a "stack extension" (rolled up metal flashing) that we put in the stack so that we could pull it down into the cook chamber to cause the heat to linger longer. Anyway this newly conceived plate would serve as a baffle / diverter so the air flow gets redirected after it clears the BP and before it rises to the top of the chamber. What do you guys think?
And to the fellow BBQ'r that asked me to recheck the stack for proper size and length I am certainly doing to do it.

Last question for the night. If you're doing a cook and you fire up your Reverse Flow Offset Smoker and cook for say 9 hours how many pounds of charcoal do you go through? We use charcoal for heat and wood chunchs for smoke. I went through two bags of Kingford bricketts with a temp of average 270 degree in 9 hours.
Thanks for your input.

[Mo Smoke]

I like the sound of that diverter plate you plan to add. Seems to me that it would slow down the rise of the smoke and heat and send the across the chamber before it is drawn up and out of the stack. Not sure, did you say your stack is top or side mounted? Post a couple of pics of your cooker if you can. Inside and out. One of the pros might spot something that answers the riddle.

[Big Steve]

Stack is top mounted, with an adjustable insert sleeve which drops into the cook chamber.
I'll upload some pics for the pros eyes.