Too much Draft?

[Cave Man]

Ok I was cooking Christmas Day and getting the temps to stop running up,to around 300 was working me to death. I was standing there and going to remove the cap off the the second stack on mynreverse flow to see if imcouldmvent more heat from the cook chamber and as I pulled off the cap from the second stack I noticed that there was no smoke coming out that stack but the other one was blowing it out like crazy. The reverse flow stack had so much draft that it was pulling in fresh air threw the offset stack. Sounds crazy to me but I stood there for about five min and watched this happen. The reverse flow stack is 17 inches tall and I had a 24 inch extention on top of that. When I took off the extention I got smoke from both stacks, the fire calmed down and the temp settled down to a respectable 240 and pretty much stayed there.

Specs: 80 gal cc , fire box is 16x16x22 HxWxL , stack is 4" squair tubing , reverse flow with about 10 squair inches of air intake.

So what's your take on why this thing set up such a strong draft? Is that good or bad ( I think bad because the temps flew up). I'm running Royal Oak Lump and Hickory for the fire.

[Gizmo]

A healthy draft is kinda like a healthy girfriend ... not something you EVER want to complain about.

On the other hand ... you DO have to understand and manage it properly ... your stack extension was apparently enough to overpower the other stack.

A predictable, repeatable draft is the nature of the beast and you'll figure it out in time.

Just for comparison - I run Edgar on 3 square inches of draft and a 4" diameter round stack that's 36 inches long but the flu is only half open. He stabilizes at 280 - 300 with the baffles wide open, 230 with them closed. fwiw

[Rodcrafter]

I would have to say that regulation on the part of exit air or intake air or a bit of both depending on wind direction at the given time is where it is at. But I agree with Rick that a good flow or flew is awesome.

My $.02

[Tom_Heath]

This may be one of the downfalls of building your own rig.

99% of the folks out there buy a rig, cook on it, make some mods, cook more, more mods and so on.

By the time that they realize it could be better, they pretty much know how there pit runs, and then they can play with the top damper to fine tune things. Adjusting the top damper is going to control your draft to a level you like and also give you the mileage that everyone desires.

Not that building is a bad thing, just that a guy gets a ton of stuff thrown at himself all at once and that makes so many variables to contend with.

[The Czar]

Really Rick? A healthy girlfriend? That is your analogy?

[Cave Man]

You guys are NUTS! Healthy Girlfriend? And Tom you are on point there and add to it someone that does not have any experience with an offset or reverse flow smoker at all. But if I could afford to buy a finished and tested rig it would have been different. That said I didn't find out about this resource till I was too deep in the build to turn back. I got lucky and it turned out ok and it cooks great. Just getting a Handel on the controls and the Knoledge that I don't have from using Smokers that are well constructed and some that are not.

So the just of it is to get the flow to keep the temp up. What I have read is that dampening down the exaust was a bad thing so I have been trying to control it with just the intake dampers. So back to the drawing board to build some variable exaust dampers for it. Mine now are on or off.

Thanks for all the input. Like from said I would be totally lost without the help.

[SoloQue]

I have dual stacks for exhaust on ole Pops. The stacks have rain covers that can be slid totally to one side or partially cover the end caps. When I had TQ build the rig I intentionally had more exhaust volume than the calculator called for. Now when I am full open exhaust I feel like I get maximum heat flow into the Cook Chamber. When I have the whole rig up into temp range and holding I tweek closed the intake to a holding temp point. When I have stalled the temp climb and the nose end has reached about 5 degrees over my main target temp which means the firebox end is about 30 or so hotter I throttle back about a third of 1 stack. When I do that small choke back on the overall air flow the nose slowly drops just a bit in temp and the firebox end drops a bit quicker down to almost within 5 - 10 degrees even closer at lower cook temps. As usual I gave more info than needed but that might help get a hand up on temp controls. If you over stall the exhaust you will kill your embers and really get too much smoke.

[Tom_Heath]

You are correct in your research, most will tell ya to run it from the intake. Yes you do need to do this in order to understand how to tune it from the stack.

So in short, when you can keep it half azz with the intake then move to the stack and damp it down from there as well. The big concern is that you dont want to have stale smoke. And you still want to have an efficient burning fire. A snuffed out smoldering fire in not gonna work in your favor.

[Cave Man]

Got me a plan to limit the exaust with a kind of a gate valve (sliding knife) design. I will also be shortening the stack down a little to 29 inches from the 41 inches it is now. That should get the draft down to a more manageable level.

Well I guess this means I have to cook on it again this week end to try and figure this out!

[Gizmo]

Sorry about the girlfriend comment - forgot this is a sensitive bunch.

In a well-sealed cooker there is always a small tug-of-war going on between the stack and the draft. I have always thought of the stack as the rough adjustment (that's why I start at the mid point so I can adjust either way if need be) and the draft as the fine tuning (because it's closer to the fire and it's changes typically show up quicker on the FB temp). After you get to know the smoker pretty well you'll notice that a more open draft makes your draft more sensitive ... since the stack can pull harder on it.

.... But I also still believe in the easter bunny....

[Smokeone]

Rick- I don't know whether to worry or complement you.

Back to the subject, I think the fellers are sending you down the right path. Trial and error.

[Cave Man]

I think complement him! all the suggestions and pointers I have got here have made it possible for me to get it to where it is now. So making it better is just one heck of a bonus! Think I'm gonna fire it up Saturday to try and regulate the output down a bit and see how it runs.

Kind of makes sense why I can't seem to get it down to the thin white smoke. I'm choking the fire by limiting the intake and not getting enough combustion. So by getting the balance between the two the fire can burn and not smolder. This will produce the heat but not the thick smoke that swims to get over powering if I'm not careful.

[Gizmo]

Now you're talking Cave Man!

[Tom_Heath]

Right on the money.

If you ever have a chance to check out a jambo, look at there air intake, Non adjustable. They set it at the factory and all you have to adjust is the stack.

Sounds like a mathamatic problem that frank is probably already working on in the back of his mind. Along with the other 5000 thoughts.