I did an 80 gallon compressor tank for my son last December. Made a terrific RF out of it using square doors that were built out of the door arc that would have been built if it were standard.this might give you some ideas.
This has a 4" square stack tha can be removed for transport and the double side by side square doors keep both internal rack sizes the same. Internal volume is about 90 gallons.
Make no mistake, there ain't no powder in this Puff ! And... I'm not really a crazy person but I play one in real life
You'll need a throat size of ~38 sq in. I think I would make a center feed (CF) with the 20 gal tank horizontally attached to the underside of the 60 gal. If you use a 4" round stack it'll need to be 19" long.
If it's tourist season, how come I can't shoot 'em?
I agree with Pete, because the small tank is thinner and the small diameter won't allow for a normal flame like an offset really needs. Where an vertical doesn't need a normal flame as an stick burner.
Making memories.
Current Smokers: Backyard RF Offset and Hybrid RF Offset trailer rig with Cowboy cooker and fish fryer, always room for more........
Thanks for the calculator assist Pete. Your input helped me understand what I was seeing on the calculator.
If going with the center firebox design, would it be beneficial to have three smaller throats ( say 2 or 3 inch pipe ) with individual dampers instead of one larger one? One piped to center and one to each side. In my untrained mind it would allow more heat control and lean itself towards eliminating hot and cold zones unless preferred.
Multiple openings are unnecessary and overly complicate things IMO but will certainly work. You will have a baffle plate with openings on each side under the cooking grate to create the heat/smoke flow to the top center stack. Making the throat opening a long rectangle would probably be the easiest but use whatever you may already have if that's not doable.
If it's tourist season, how come I can't shoot 'em?
You're right Pete. I can see where the long, narrow, rectangle throat opening with a larger deflector plate would do a good job of heat distribution with these two tanks. That would be a pretty simple fab-up too.
As for that top center stack,,,,as the smoke comes around the deflector plate, does it form a sort of pyramid up to the center exhaust or should it sufficiently fill the whole chamber with smoke? Is there a general consensus on how far into the cook chamber it should protrude in order to insure any and all meat in the center gets kissed by the smoke?
Well I don't have any cool drafting programs,,, but I have become pretty proficient with MS Paint. Sat down today and made up a concept drawing. I'm thinking about making the firebox/cook chamber connection with some angle iron flanges so if later the firebox needs to be changed out it should be a simple process. I'm still debating the firebox access. I'm considering making a basket that slides out of one end, rather than a flip down panel.
nice MS paint picture!!
a coworker of mine built a center FB RF using a tank similar to your smaller 20 gal. as his CC and a cut down tank for the FB, he likes it alot! You are gonna have a good smoker!