Stack/Draft debate

[Gizmo]

There seems to be a debate raging for as long as I can remember about how to control a cooker:

Set the draft and adjust the stack…..
VS.
Set the stack and adjust the draft……

This might just be a chicken and egg subject but this is my take on it....
Note: everything I'm going to say assumes the rig in question is properly sealed - otherwise it's a crap shoot.

I think the draft and stack are 2 parts of the same adjustment and should be sdjusted in tandem.

The most important setting to determine on a new smoker is the "PEAK" position on the draft.

With the STACK WIDE OPEN through test burns I try to find the "peak" setting on the draft where I can generate the most heat in the CC. Takes me a whole day or weekend and at least a bag of charcoal so I don't even try to cook anything beyond a pound of bacon.

Cause you just can't screw up bacon…
….or have enough of it around….
….or beat it as a seasoning food for a new cooker ….
….but I'm getting off the subject.

You can have the draft open too far and the temp stabilizes but closing the draft actually brings the temp up - reason being is that when we let in too much air the fire burns only what it needs and leaves the rest to mix with the hot air it produced which lowers it's overall temp. Finding this benchmark temp is everything to knowing how to get the rig to behave. This temp rise/drop may only be a few degrees but it's a serious important thing to know.

Since I'm breaking in Earl today I'll use him as an example. I'm guessing he'll peak at about 2 inches open - which is a total of about 6 sq. inches total draft area (draft door is 3 inches tall). I'll know more by this time tomorrow.

Then I put in the meat and see where the temp drops to. Note: How much meat as a percentage of the total CC volume - direct from the fridge or off the counter … yada yada yada … is a subject for another thread.

Once the meat is in if the temp is where I want to cook at then I leave it alone. I also plan on attending church services because that there is a miracle worthy of note! If it's too hot I'll drop the draft down by a fraction - i.e. 1/2 the peak, 1/3 of the peak, 3/4 peak, etc. Notice these are fractions of the PEAK opening size - NOT the total Draft size you built into the cooker.

Now I put the stack at that same fraction but SLIGHTLY TIGHTER (smaller). In other words the stack is a little further closed than the draft - it's leading in the movement toward being closed.

The reason the stack has to "lead " the draft is because at the stack end of the process the air is hot, full of energy and trying very hard to go up and out. The restriction (flu damper) in the stack is there to HELP the draft do it's job. If we let 4 million molecules of hot air out the stack then we will have to let 4 million molecules of cold (ambient) air in - that's physics. So the VELOCITY is very different - the Draft is always slower than the stack - sort of like letting marshmallow cream into the system and water out of the system - same number of molecules but very different density and velocity to maintain the balance. Thick and slow vs. thin and fast. Since the velocity is so different the stack needs to be slightly smaller than the draft to help the draft restrict the airflow properly.

If we leave the flu damper wide open then the stack is pulling too hard on the system and diluting the effect the draft has to restrict the incoming side.

Clear as mud?

So there. Thoughts to ponder ….. or at least start a good argument….

[Clover Ridge Smokers]

You must be bored Rick.......ha ha ha

Thanks for the insight. After several burns, I determined I needed to make adjustments to both the stack and the draft for optimal performance.

[Gizmo]

CRS if you listen very closely you can hear all the other readers of this site mumbling something like "Gizmo's lost it - everybody step back quietly - just tip toe away from this thread and maybe we won't get sucked into the vortex of this mind-numming subject ….."

So since everybody is ALREADY giving me the WTF look I'll finish with Earl's peak draft:

9 square inches.

That's for a fire consisting of a lit #10 can of briquettes with an unlit #10 can on top of it to build heat. Note: a #10 can is about 3/4 of a standard Walmart chimney worth of briquettes (55 to 60).

So Earl's starting fire was about 110 briquettes with the bottom half lit.

By comparison:

Edgar's peak draft: 15 square inches.

That was 2 lit chimney's with 1 unlit chimney on top to build heat. About 225 briquettes with the bottom 2/3 lit.

Edgar wants a #10 can of briquettes every hour.
Earl wants a 303 size can of briquettes (25ish) every 45 minutes.

My rule to maintain some consistency is to add fuel as soon as all the coals in the fire have turned white. Any convenient measuring device will work - including the chimney itself. But stay consistent. This stuff is boring - UNTIL you're asking yourself; "how much fuel should I add?" … "how often should I add fuel" or "why is this CC temp such a roller-coaster compared to the last time I cooked on it?"

If you're consistant - the cooker will speak to you and teach you how to do it right …. which is part of the addiction

[SoloQue]

Pops likes a steady diet of 3 healthy splits every 45 minutes when I am smoking with ambient temps between 50 and 80. Any hotter and I back off a split and any colder I add a split. If I am smoking in freezing conditions a welder's blanket keeps Pops in the target zone. If I ever see that the burn rate has reduced my overall coal level I toss in about 20 briquetts to boost the burn and get everything back to what I feel is normal. As for the Draft, I don't mess with the stacks until I have my cooker is fully up to temp in the coolest zone and the intakes have been dialed in for the expected cook range then I close both stacks about 25%. (I intentionally had Pops built with oversized stacks to allow for serious air pull when needed such as start ups or excessive temp loss recovery) At this point I see a flattening of the temps across the zones with maybe a 5 - 15 degree loss in temp around my hot spots but almost no loss in the cooler zone (lower nose). I am really convinced that intake positin in relation to basket position within the FB is critical for optimizing fuel consumption vs heat output. I now run with a center feed intake below the front of the basket that places the coals in direct line with the throat of the cooker. All air goes through the coals and when I tweek the stacks that air just moves a bit slower gathering that much more heat without the need to oversize the burn of the fire. As far as determining this stuff, I loaded Pops with 6 therms and took readings every 15 minutes over a 10 hour burn. You either have to be really bored or really curious to kill a day running an empty smoker and taking temp readings but now I can tweek with confidence or better yet know when not to tweek but just adjust fuel quantity.

Solo Out

[Gizmo]

Thanks for sharing Solo - I know that took a lot of courage to admit the loss of a day just running temps - even if it's worth it!

[Smokeone]

This is a great topic. I can't add much here as I am currently using pellets and a UDS. But of course I have a little thought on it.
I like to control with intake air and save the exhaust to block a little heat if I have a drastic fall, like when you add meat, and to stop a run away fire.

Yep now I don't even know what I said.

[Gizmo]

S1: Yep now I don't even know what I said.

And THAT's what makes this a great topic! ….. all those words and I STILL didn't get anything said

Seriously though S1 - I bet there are more people doing it the way you just said than any other way.

I guess I'm just funny that way - can't leave it well enough alone ….

[Miketheforester]

I probably need to sharpen up on Running my pit a little. I have tried messing with the stack some and had white smoke as a result, but they where really uneducated attempts. It seems like my pit does have a happy spot but it is on a knife edge between struggling to keep temp and 325*.

Sent from my SAMSUNG-SGH-I847 using Tapatalk 2

[Gizmo]

Been there …. sort of like stacking BB's

[SoloQue]

The sweet spot for Pops is 225 when I am running with just the bottom clean out plug removed. It is almost an auto setting. Often I will run the CC up to 325 prior to loading the meat. Once I get everything in place and shut up tight I slowly close the side intakes at about a full turn a minute until both sides are closed. By doing that I haven't starved the fire during the process and I'm back down to 225 in about 15 minutes. If I ratchet everything shut too quickly I get white smoke and the temps can drop through the zone since I didn't let things mellow as they dropped.

[Gizmo]

Solo have you noticed a predictable temp drop related to the amount of meat you put on? Like a lot of drop from putting a lot of meat etc…?

[SoloQue]

If I am going to load up something close to 60% or more of my capacity I can see a 40 degree plunge or more as I push the capacity limits. As a rule I leave the meat I intend to smoke in the frig right up to smoke time because I want to prolong that smoking window of reaching 140F to give me a better smoke ring. Each one of those chunks of meat are just heat sinks in disguise in my opinion so I plan ahead and over shoot my target temp before loading. Of course it doesn't help that cooking 80 lbs of wings takes a while to get loaded onto the grates.

[Rodcrafter]

Wow this is a great topic. I've been away from my computer this weekend, so excuse me. I have a different type of smoker than many other people and it works a lot different than they do as well. I have a vertical and a horizontal CC, both have a BP and both have stacks. The vertical is opposite from the FB, the way the stack changes the temp in each works so different. When I get them both to 225 or about that temp. I start closing the V. CC stack about 1/2 then the H.CC stack by 1/4. Because the air going up in the V.CC is more vigorous than the air in the H.CC. I have to attract the air to the stack in the H.CC to keep the temp up because it wants to go out the stack in the V.CC. Like electricity is takes the easiest course of escape. Once I have the temps balanced out I can turn them up or down together by the intake air vent because it is shared.
I have to admit, I have invested the time it takes to find this out. But it is so valuable when I'm trying to get the real cooking done.
Unlike Solo, I take the meat out of the fridge when began building my fire, because I don't want that much of a heat sync effect when loading very heavily. I feel like the smoke will get to it enough, but that is just me.

jm2cw

[Gizmo]

Many thanks for contributing guys. It's surprising how important this subject is but nobody seems to say anything about it. Obviously several of us devote time to "dialing it in" before gambling real meat on the process.

If I were brand new to this hobby today I would read and re-read this stuff to help gain some insight before I lit my first fire box.

One observation I will share because these posts reminded me: Based on all the smokers I've ever operated, an overshoot of 30 to 50 degrees would be a good rule of thumb starting point for adding meat to end up back at the temp you are aiming for to cook at. As I say that - I'll admit that Earl ran closer to needing 70 degrees of overshoot but has the shortest recovery time of all of them - I think both of those characteristics are because he's so small. I suspect bigger pits are smoother operators…? For me, nothong was smoother than Edgar. (less roller-coaster behavior with temp)

Hopefully someone will disagree with me here - cause we'll prolly all learn something … ?

[Rev.Mike]

i agree with you rick, and the next time i fire up one of my smokers, it will be a test burn, and use some of you fellers suggestions and see what happens, only got time ti kill anyways, and i got plenty of that ive read this thread a number of times, and made me think Great info!

[SoloQue]

One thing about these heavy weight RF rigs the thicker metal really helps recover the cool down period of loading up since they are so stubborn about cooling down themselves on their own. Good thread Rick, I know I had some crazy extended cooks early on when I was doing a full load and I was literally at cooking temp when I tossed everything on. I was stuck stoking up a larger fire to compensate and suffered way too much heavy whhite smoke through the process. Lesson learned to saythe least. I still get inquiries from friends who want to be my therm watchers when they come over for a tailgate get together.... too hot ...too hot ... then I get to watch them just start nodding in agreement when they see the final temps when the door gets sealed.

[SoloQue]

For me, nothong was smoother than Edgar

Edgar is a center FB design yes? I've got to believe that design allows for the most agressive recovery since you lose so few btu's as compared to an extended pipe having to heat everything along the way while the air is actually cooling in the process.

[Gizmo]

I agree Solo - that added to the insulated walls HAS to help…

[Rodcrafter]

[Frank_Cox]

awesome thread guys!!!
and this is what makes TRUE PitMasters!

[Rev.Mike]

took gizmos advice today with my smoker, started with 2 full chimneys of coal, and added 2 splits, let the cooker come up to temp, and started slowly closing my drafts and stack damper, once it settled in at 250, i was adding 2 splits every 45 min, the temp out was 25 degreese, didnt cook anything just a curious pratice burn in cold weather. i noticed that my damper was closed about 3/4 the way, and the temps held, seems odd to me but it worked

[Gizmo]

That's great Rev.mike. Now that you know the baseline setting you'll never be too far away from where you want to be when you adjust for a "load"

[Clover Ridge Smokers]

Practice make perfect

[Puff]

Gizmo, I think this is more interesting than most anything I have read with regards to the use of a smoker. I question this part though, most things that I've read say the stack is always wide open. To that comment , many of the smokers I have looked at for sale by builders and not commercial manufacturers APPEAR to have stack covers but no mention of adjusting it for CC control. Since my 6" diameter stack terminates at about 8 feet 7 inches, I'll need to develop a system for moving the cover over to reduce the stack diameter

Again that is my very novice understanding. By the way feel free to elucidate further on these topics...especially the one about bacon being the perfect seasoning cook. These topics are not covered anywhere I've looked and they are really are very very good

[SoloQue]

By the way feel free to elucidate further on these topics

OK, that has got to be a 4 beer sentence ... maybe and just maybe after 4 beers I will be able to comprehend what I am reading

especially the one about bacon being the perfect seasoning cook.

In reality Gizmo's reference to bacon is way too complex. It should be simply say ... BACON IS PERFECT. When you take that approach it just doesn't need an explanation.