Need help with firebox design

[heihei29er]

Hoping to get some help from the community on a firebox design decision.

I have a 250 gallon DIY oil tank converted into a rotisserie. We have an ash pan that serves as both indirect heat and a sloped drip tray. The ash pan slides in/out, and we pull it out to load fuel versus opening the door. It works great, and we've done some great cookouts with it. You can see the ash pan and center drip tray in the picture below.

We're making some mods to seal it up, add a RF plate and some meat racks, and have the flexibility to use it as a reverse flow smoker. Part of those plans requires removing the existing ash pan and adding a firebox.

I've done all the calcs and have no issues there. Roughly, I need a 24" x 24" x 24" firebox. The question is with how draft and the FB/air vent/stack volume calcs are impacted by the two different designs I've come up with for the firebox.

Design A is more typical of what you see on RF smoker builds, and it requires hanging the firebox off the back of the trailer. However, it has a long plenum between the FB and the CC, and I have concerns with heat loss and temp control. Red is the trailer frame and black is the CC.

Design A

Design B makes the plenum more compact and should be much better with heat loss, but requires the draft to flow down before entering the CC. Wondering how much impact that down flow would have on the natural draft of the smoker, and if a lot, what mods are recommended to the air vents/stack height/stack diameter/etc. to compensate for it.

Design B

Thanks for the input and help!

 

[mike243]

How would a RF be better than a set of tuning plates? is it worth the $ and fab when plates are a cut and slide in? the fire box could either be bolted or tabbed and pivot from the top and the weight of it can seal it and still retain the use of the charcoal box if needed.that way you can always step back to the way it was with less hassle

 

[mike243]

A is the better way to go ,heat wont like to go down and ash may get drawn in more also a taller smoke stac will be needed probably to create enuf draft,fire box could still be hinged to keep it from hanging down too much while hauling

 

[mike243]

With the charcoal pan in and a grate across the whole width is 1 big old charcoal grill for direct grilling with out doing much more than setting tuning plates out and dropping the lid on the pan opening,you have a great machine that wont take much to mod it to be a offset smoker imo and wouldn't try a drastic change but talks cheap and metals high lol good luck

 

[heihei29er]

mike243 Thank you for the responses!

I have a Brinkman TMLE modified to a RF and don't have any experience with tuning plates, so my mind immediately went to RF when we started thinking about mods. Will have to give the tuning plates idea some thought. The current ash pan/drip tray was our original design. It works well overall, but airflow is poor and we periodically have to pull it out and stir the coals to revive them.

I like the idea of hinging the FB and using the weight to help with the seal, and you're on the same page as my BBQ partners and me. We want to be able to swap out between using it as a smoker and using it as we currently do.

Will keep you posted as it progresses.

 

[mike243]

Do you have a grate in the charcoal box now? If not that would stop the need for stirring more than likely

 

[heihei29er]

No grate yet. It's been one of those "we should do that" projects that never gets started.