Hybrid Smoker Build Design Feedback

[hooligan2]

I have a 120 gallon propane tank I am going to convert to a hybrid reverse flow half and grill.  I have attached some pics of the sketch up design I have been putting together.  I am ready to start building, but I would like some feedback with regards to the overall design and specifics on the fire box.  The FB was oversized according to the calculator by 170% because I am using part of the tank as the FB and wanted the top door about 14" for convenience and also I wanted to leave room for an ash pan.  So, I reduced the size of the FB using the calculator to determine the actual metrics needed for the intake, exhaust and FB2CC opening.  Is this sound reasoning?  

Orginal Calculations

Link to BBQ Pit Calculator

Modified

Link to BBQ Pit Calculator

 

[hooligan2]

Here are draft images of what I am designing.

HybridSmokerFrontView.jpg

• hooligan2
• Jan 11, 2015

HybridSmokerFBview.jpg

• hooligan2
• Jan 11, 2015

HybridSmoker.jpg

• hooligan2
• Jan 11, 2015

 

[daveomak]

Add upper air vents.....

HybridSmokerFBview.jpg

• daveomak
• Jan 11, 2015

 

[hooligan2]

I have a sliding air vent in the middle already.  Are you suggesting it should be higher?   I was planning on notching out he side of the tank as in the image below but just for the air intake.  The ash pan would is at the very bottom of the tank and would slide out.   

900x900px-LL-0f2c6d23_006.jpeg

• hooligan2
• Jan 11, 2015

 

[daveomak]

The bottom air inlet to the FB, controls the temp of the fire..... The upper air inlet moves the heat from the FB to the CC.... using the two inlets in unison, allows for perfect controlled temps.... throughout the smoker....


Usually folks build with the lower air inlet below the fire grate, and the upper inlet across from the FB/CC opening....

 

[hooligan2]

I got a free lab workbench from work and i am considering using it a the frame for the CC since it already has casters.  I figure I would need to weld angle iron to support the two legs.  However, I can't decide how to mount the cook chamber.  The top of the frame sits about 33" off the ground, so the main cooking grate would be around 45" if I just mounted it as is.  That seems a little high and am worried about the stability of the frame at that height.  Or I thought I could cut down the legs so they cooking grate would be at 36".  I modeled this with cardboard in the pics.  Any other concerns using this frame or should I just build one like I laid out in my original design?

20150113_203202 (1).jpg

• hooligan2
• Jan 13, 2015

20150113_205422.jpg

• hooligan2
• Jan 13, 2015

20150113_210256.jpg

• hooligan2
• Jan 13, 2015