Vertical reverse flow insulated build - Advise and wisdom wanted!

Discussion in 'Reverse Flow' started by jad pit, Nov 17, 2014.

  1. Hello SMF!

    A couple mates and I have been BBQing on a simple bullet smoker that we went 3rds in a few years back and have really gotten hooked. So much so that we've decided to take the next step (well... leap) and build a smoker of our own.

    Being based in Australia it's hard to go see a smoker of this type in the flesh, but after looking at many build threads and pit maker websites we drew up the following designs.

    The measurements are in millimeters and inches. Happy days! 






    I would appreciate any feedback from you more seasoned BBQers and builders on our design and I'm sure I'll have a lot of questions along the way.

    For a start, we are planning on putting in 2x 50mm (2inch) gate valves for air intakes. What is the best position for them? Do we need to have 2?

    What gage steel should we use for the inner skin and outer skin?

    I had a friend look over the plan and suggest we line the top of the fire box with heat resistant ceramic tiles (like a pizza oven) to act as a dampener so the steel plate above the fire box can be thinner. Sounded like a good idea. Is it?

    I've looked at BBQ ratios but can't find any rules for this type of smoker, do horizontal BBQ ratios still apply?

    Is the position of the flue intake correct? Is the flue big enough?

    Are the channels 25mm wide x 600mm long (1inch wide x 26.3inches) big enough for the reverse flow channels?

    Ok that's probably enough questions for now! 
     
    Last edited: Nov 18, 2014
  2. I will see if I can get DaveOmak to take a look.

    Happy smoken.

    David
     
  3. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    I take for granted the heat channels are on the sides.... The exhaust is in the center of the back....


    For a start, we are planning on putting in 2x 50mm (2inch) gate valves for air intakes. What is the best position for them? Do we need to have 2?


    What we have determined about the fire box on a smoker is.... 2 air inlets dramatically improve the heat/smoke/air flow of the smoker...
    The upper air inlet allows the ability to move heat, increase air flow, and possible cool the smoker when necessary..... All without adding oxygen to the fuel and increasing the heat...
    The lower air inlet, should be positioned below the fuel so as to regulate the heat output......



    I had a friend look over the plan and suggest we line the top of the fire box with heat resistant ceramic tiles (like a pizza oven) to act as a dampener so the steel plate above the fire box can be thinner. Sounded like a good idea. Is it?



    I'm a fan of installing a 1/2" / 12mm plate between the fire box and the cooking chamber, in the vertical reverse flow smoker... Strictly for conducting heat to the cook chamber.... In that installation scenario, a mildly smoldering fuel supply will heat the cooking chamber... The upper air valve can be used to move the heat from the FB to regulate the CC heat..

    The exterior walls should be well insulated.... If the smoker is used in the range of 120 - 350 F, I would think 3/16" interior plate and 16 gauge exterior sheet metal, with 1-2" high temperature insulation would make a fine smoker..

    Have the heat channels and exhaust channel on the inside of the smoker... well insulated...

    I would lower the exhaust channel to the plate separating the FB and CC... You shouldn't need a water pan... they are used in poorly designed smoker for sucking up BTU's.... a small pan can be used to add a small amount of humidity when necessary...
     
  4. Thanks for jumping in here Dave. As always you are a wealth of knowledge.

    Happy smoken.

    David
     
  5. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    As for the "Air flow channels", whether inlet or exhaust, remember this is a "gravity flow" or "convection flow", where the difference in density of the air generates the air flow... There's a delicate balance that makes it work.... Friction, from the air channels, whether inlets or exhausts, can greatly influence how that system works... Sooooooo, reduce the friction influence by increasing the area vs. surface area of the channels..... I have no idea what that ratio should be....

    Here's what I mean...

     
    Last edited: Nov 20, 2014
  6. Looks good, here is one we built a couple of years ago

































     
  7. Cheers for pointing that out Dave!

    I studied the thread where you posted those pics originally Gary. It was a big inspiration to get building! Looks great!

    I hope we can come up with something similar.
     
  8. It looks good.

    Happy smoken.

    David
     
  9. I like the idea you posted as per Dave O.  Vents and air flow are critical.  Ours was a proto type which works great. If we did another one like that probably would go with the vent system you are going with.

    Gary
     

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