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Designing a reverse flow horizontal to vertical smoker?

post #1 of 7
Thread Starter 

Hello, I have been lurking about for a while now – reading up and learning.  I soon will be tackling my own reverse flow smoker build, and wanted to run a few things by the group.

I have acquired a used 37.5” diameter by 10’ long propane tank that is in pretty good shape and I am considering how best to make it into a proper reverse flow meat smoker. I am thinking of converting it so that roughly 6’ to 8’ of the tank is configured in the horizontal position and then adding ¼” steel to form a vertical box smoker at the end – so in an “L” shape when viewed from the side. As might be expected, the fire box will be under the vertical cooking chamber feeding the underside of a ¼” thick steel baffle plate that directs the smoke to the far end of the horizontal cooking chamber.

 

Hopefully my intent can be seen in the attached illustration. The blue cigar shape represents the tank as the horizontal cooking chamber. The green square box in the upper left is the vertical cooking chamber. The red box to the lower left is the fire box and the extension of the baffle plate (in red) into the horizontal cooking chamber.

 

 

 

Question: I am wondering about the wisdom of the horizontal AND vertical cooking chambers setup with only one firebox feeding both?

 

I have seen some smokers very like this design, and I have seen others where the vertical chamber is setup not for smoking but to create a warming box. My thought is to have two pairs of chimney pipes – the first pair (colored red) for exhausting the horizontal cooking chamber as can be seen with the thick yellow line representing the flow of smoke.  And a second pair (colored orange) for exhausting the vertical cooking chamber as can be seen with the thick dashed yellow line representing the flow of smoke.

 

I figure I would have a small adjustable opening between the firebox and the vertical cooking chamber so I could close off and isolate the vertical chamber to prevent the entry of smoke and additional heat – so it would be used for keeping food warm.  However, if I desired to use the vertical chamber for cooking and not warming, I could open the door between the firebox and the vertical cooking chamber.  And if I only wanted to use the smaller vertical cooking chamber, I could have a door to close off the larger horizontal cooking chamber and be able to have a much smaller fire in the firebox.  Hopefully that makes sense.

 

Another Question: Does having one of the cooking chambers right on top of the firebox create a significant amount of heat? In the illustration I added what is supposed to be fire brick at the bottom of the vertical cooking chamber. Is this overkill or a wise idea?

 

And yet, another Question: Regarding the stacks/chimneys: I have seen some builders state having the intakes (for exhausting the smoke) at the bottom or just under the level or plane of where your meat is placed. This implies that your meat is sitting in a constant cloud of smoke and heat. However, I have seen other builder’s state that the stack/chimney intakes should be at the top of the cooking chambers there by having much better air flow and less stale smoke.  Can someone please speak to the pros and cons of each design?

 

Anyway, I welcome any thoughts and ideas you all may provide. Particularly important notes and things I should make sure I am aware of and account for. I am wise to Feldon’s excellent calculator and have been plugging away at it. I just want to make sure I have a sound idea and understanding of what a proper smoker design should be.

 

Thanks, -blakeman

post #2 of 7
My two cents....


On stack height, I've decided I like them flush with the top of the inside of the tank. I like the cooker to breath well and not hold the stale area. But some like that heavy smoke flavor...just not for me.

So, on your vertical cooking chamber, the way your design shows it feeding straight from the firebox....what is your thinking on that? Are you wanting to just cook in one cooking chamber at a time? Is there a reason you don't want to use the same draft from the horizontal CC? So what kind of temp. Range are you looking to get in the vertical CC?
post #3 of 7

I do not much believe in the concept of "stale smoke". The cook chamber is a dynamic environment where the smoke has no opportunity to become stale. The difference is only in the path the smoke travels from the the end of the RF plate to the entrance of the stack. A stack opening flush with the top of the CC provides a more direct path. A lower opening will allow the smoke to remain in contact with the meat a little bit longer as it travels the extra distance to the opening. There will also be a bit more turbulence with a lower stack opening. The upshot is that the lower stack opening will impart a stronger smoke flavor to the meat than the opening flush with the top of the cook chamber. Of course that is JM2CW. YMMV.

post #4 of 7
Thread Starter 

Quote:

Originally Posted by Ribwizzard View Post

[O]n your vertical cooking chamber, the way your design shows it feeding straight from the firebox....what is your thinking on that?

Still working out that idea.  Hopefully I can find some existing smokers that have successfully employed such a design.  I am thinking I will employ a baffle plate of sorts below the opening to the vertical cooking chamber and make some sort of adjustable slotted gate/door between the firebox and the vertical cooking chamber - allow me to adjust how much heat and smoke can enter.  I would also have an adjustable door/gate feeding the horizontal cooking chamber to block it off is so desired.

 

Quote:
Originally Posted by Ribwizzard View Post

Are you wanting to just cook in one cooking chamber at a time? Is there a reason you don't want to use the same draft from the horizontal CC?

I would like to be able to use both chambers at the same time for a big cook, but also alternate between the horizontal and vertical as needed for smaller cooks.  The primary reason for not drafting through the bigger chamber to the smaller is if I wish to only use the smaller chamber I can block off the bigger one and use a smaller fire.

 

Quote:
Originally Posted by Ribwizzard View Post

Range are you looking to get in the vertical CC?

 

I would like to be able to obtain temperatures between the hundreds to three hundreds in both chambers.  Not sure how well I would be able to create a drastic difference in temps between the two chambers, but if I could get fifty to a hundred difference between the two - that would be awesome.  I know it would be a challenge too, but then again we all are presently reading posts in the "smoker builds" section of the forums.  You are not here reading in this area without already having stepped up for a challenge in the first place…

post #5 of 7
Thread Starter 

Ok - so I have four coppers in the kitty:

 

Quote:
Originally Posted by SmokeJumper View Post
 

I do not much believe in the concept of "stale smoke". The cook chamber is a dynamic environment where the smoke has no opportunity to become stale. The difference is only in the path the smoke travels from the the end of the RF plate to the entrance of the stack. A stack opening flush with the top of the CC provides a more direct path. A lower opening will allow the smoke to remain in contact with the meat a little bit longer as it travels the extra distance to the opening. There will also be a bit more turbulence with a lower stack opening. The upshot is that the lower stack opening will impart a stronger smoke flavor to the meat than the opening flush with the top of the cook chamber. Of course that is JM2CW. YMMV.

 

Quote:
Originally Posted by Ribwizzard View Post

My two cents....

On stack height, I've decided I like them flush with the top of the inside of the tank. I like the cooker to breath well and not hold the stale area. But some like that heavy smoke flavor...just not for me.

 

 

How does this idea grab you guys?  Go on ahead and install stacks that go deep into the chamber – promote more smoke flavor, but have holes cut in the upper part of the stacks up by the ceiling of the cooking chamber.  I can get a set of the stainless exhaust pipe band clamps (http://www.summitracing.com/parts/vpe-1177?seid=srese1&gclid=COLt8-TThb4CFewDOgodwy8Aag) used on the big rigs that I can use to cover the wholes when I want big smoke or slide out of the way when I wish to have less.  Only problem with that idea is I am not sure how that would affect my stack volume and proper flow.  Hmmmmmmm

post #6 of 7
Size your stack as if it were exiting at the top of the CC and it will be just fine when extended to a lower opening.
Draft is not determined by the position of the stack opening in the CC, it is determined by the height of the stack above the fire and the amount of heat retained in the smoke.
Holes in the pipe will cause restriction in flow, so you would be better off with a short (1" - 2") section of pipe extending down into the CC to which you can clamp on a pipe extension for a lower opening.
post #7 of 7
Thread Starter 
Quote:
Originally Posted by SmokeJumper View Post

[Y]ou would be better off with a short (1" - 2") section of pipe extending down into the CC to which you can clamp on a pipe extension for a lower opening.

 

Could do that, or just weld the pipe to the top of the chamber and if I think I need more smoke, take a roll of aluminum flashing, roll it up into a tube and stuff it into the bottom of the stack.  Same result on the cheep and quick without having to mess with any structural issues.

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