Smoke stack lengths effect on drafting?

Sid Post · Nov 18, 2019

Assuming you have a properly drafting offset smoker, keeping diameter the same, will a longer smoke stack draft better? Would a Venturi also help the draft like I see on some of the Lockhart/Austin Texas 'break over' stacks on the propane tank builds?

Also, if this belongs in a subforum I missed, feel free to move it. :wink:

ebijack · Nov 19, 2019

In my experience. Yes you can get more draft/pull. But do you need/require it?
But to what end. When the draft/pull is so much that it pulls the heat thru to fast. Burning more wood. Less heat/smoke to cook with as the air goes by to fast to do what you want it to do.
When I built mine. The flames from the fire were pulled into the cook chamber by 3 to 4 ". I shortened my stack to cure that. I've had to do that on a couple of my builds.
You are looking for draft. Not suction. If that makes sense.

quamdar · Nov 19, 2019

Yes, the longer you go the more pull you’ll get.

Sid Post · Nov 19, 2019

ebijack said:
In my experience. Yes you can get more draft/pull. But do you need/require it?
But to what end. When the draft/pull is so much that it pulls the heat thru to fast. Burning more wood. Less heat/smoke to cook with as the air goes by to fast to do what you want it to do.
When I built mine. The flames from the fire were pulled into the cook chamber by 3 to 4 ". I shortened my stack to cure that. I've had to do that on a couple of my builds.
You are looking for draft. Not suction. If that makes sense.

With more draft, don't you have more control with different wood types to keep that clean 'blue' smoke? You can 'throttle' the fire with the air intake to ensure you have a good burn while getting good air turn-over in the cook chamber.

zippy12 · Nov 19, 2019

I increased mine and I get more thin blue smoke no the cloudy white crud because the fire now burns clean...

ebijack · Nov 19, 2019

Sid Post said:
With more draft, don't you have more control with different wood types to keep that clean 'blue' smoke? You can 'throttle' the fire with the air intake to ensure you have a good burn while getting good air turn-over in the cook chamber.

If there is good draw/drafting. Adding more draw would not be beneficial.
Choking down the intake could be done. But why, if there is good drafting.
Poor drafting, yes adding more draw would be of benefit.
But to add more draw, just because. You could, but why.
Unless you like to make modifications to find what does/doesn't work for you.
Your original question was "Assuming you have a properly drafting offset smoker" not about poor drafting. Adding more exh so you can choke down the intake. Would be increasing air flow speed.
With good/proper drafting. I don't see any advantage to having over draw/drafting. You just burn more wood in my experience with no benefit. But that is me.

mcdeadstein · Nov 19, 2019

ebijack said:
If there is good draw/drafting. Adding more draw would not be beneficial.
Choking down the intake could be done. But why, if there is good drafting.
Poor drafting, yes adding more draw would be of benefit.
But to add more draw, just because. You could, but why.
Unless you like to make modifications to find what does/doesn't work for you.
Your original question was "Assuming you have a properly drafting offset smoker" not about poor drafting. Adding more exh so you can choke down the intake. Would be increasing air flow speed.
With good/proper drafting. I don't see any advantage to having over draw/drafting. You just burn more wood in my experience with no benefit. But that is me.

The top places in TX use pits that have tons of draw compared to most home smokers in terms of volume of air moving through the pit. They are wanting to move air through the pit. It helps the fire burn cleaner, gives them more convection, and allows them to 'push' the briskets more at the end of the cook. Some of the pits have frames right after the throat that fit hotel pans of water. Also they have large fireboxes and the fire is built more towards the entry so even with the large amount of draw not many flames make their way into the pit area.

ebijack · Nov 19, 2019

mcdeadstein said:
The top places in TX use pits that have tons of draw compared to most home smokers in terms of volume of air moving through the pit. They are wanting to move air through the pit. It helps the fire burn cleaner, gives them more convection, and allows them to 'push' the briskets more at the end of the cook. Some of the pits have frames right after the throat that fit hotel pans of water. Also they have large fireboxes and the fire is built more towards the entry so even with the large amount of draw not many flames make their way into the pit area.

There is a big difference in the drafting requirements of a 500 to 1000 gal smoker. Compared to smaller/shorter home units. There is also a difference between say a Shirley/Lang smoker when talking about size of smoker compared to the exh size/dia and height. When comparing to average "home use" smokers.
Every offset has a requirement for proper draft between the exh and intake.
Most box store smokers have to small of dia exh and to short on height/length. IMHO

Smoke stack lengths effect on drafting?

Sid Post

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ebijack

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Sid Post

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zippy12

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mcdeadstein

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ebijack

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