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post #1 of 36
Thread Starter 

I am new to this forum. I have just came across an old air tank that I want to build into a RF smoker. The tank is 70in long with about a 22in diameter. I do not need one that long and I thought I would cut some off the end to use as the firebox? Don't know if this is doable or a good idea? I know it will require some extra fabrication but maybe better than having a firebox built. Any advice would be appreciated. I have a fried who will be doing all of the welding for me. I am supplying the materials and information to make the build.

post #2 of 36
If you are using the tank for CC and FB, cut off 1/4 of the tank for the FB.... Then the FB will be 1/3 of the CC and that's a good size...
....Click on pics to enlarge.....


CC volume .... Dia. x Dia. x 0.7854 x Length = cubic inches

post #3 of 36
Thread Starter 

Thanks for the pictures. The FB shown is square but I get the point. Does the FB need to be mounted underneath the CC or can it mount low on the side. My thought was after the tank was cut I would weld flat plates on each open end and then cut the openings in the FB and CC and attach the FB low on the CC. Does this sound right?

post #4 of 36
The bottom picture depicts a round to round configuration.... and calculations for a FB/CC inlet...
post #5 of 36
Thread Starter 
Should I mount the FB like the last picture shows or turn it and mount it long ways. I assume mounting the way the bottom pictures show would be the easiest? Should the FB be under the CC or is mounting low on the side OK? Thanks for any advice.
post #6 of 36
Most folks mount the cylinders end to end... Although, a rectangular FB is easier to fit up, can be made with more room under the fire grate for ash collection, and the door can be sealed somewhat easier, and air inlets are easier to fabricate....

48" long smokers seem to be the norm.... I would leave the round end on the CC.... 48" from the weld on the round end to the cut would work... or shorter.... depending on what your cooking habits may be... There are several designs that work.... The RF smoker seems to be the favorite...

Instead of RF smoker, there is the Side Fire Box with tuning plates...

post #7 of 36
Thread Starter 
I have another question. I also have another tank that is 36 by 20. I will mostly be doing small cooks with the occasional big tailgate cook. Should I use the smaller tank and build a square FB or go with original plan as above with the bigger tank. The draw back to the big tank is that it is very heavy. I for sure want to do a RF smoker. Thanks for any advice.
post #8 of 36
You have to determine which size is best for your situation.... th_dunno-1[1].gif
post #9 of 36
Thread Starter 
I have decided to go with the 36 in long with a 20 diameter. I figured a a 16x16x16 FB an exhaust of 27 inches with a 3in pipe, 1 4 in air intake and a FB to CC of 33 square inches. How much area do I need at the end of the plate and how far of the bottom of the plate need to be? Thanks for any help.
post #10 of 36

You will need to multiply the 33 square inches you got from Feldons by 1.5 to make sure it flows well for reverse flow since the calculator covers standard offset also. Since your firebox dimensions are 108% of what is required, you can get by with using 30 square inches as the basis. So, you will need about 45-50 square inches from the firebox to the cook chamber. This works out to be about 4.25 inches above the bottom of the cook chamber and the line across the cook chamber will be 16 3/8" wide. It should match up well with your firebox width if the 16" is the inside dimension. The RF plate will run the length of the cook chamber 4.25 inches above the bottom and use that same 45 square inches for the gap opposite the firebox where the air needs to turn up towards the cook grates. If your RF plate is ~16 inches wide, a 3" gap at the end will give you 48 square inch opening. Hope this helps and good luck with your build, keep us posted.



post #11 of 36
Thread Starter 
Thanks now I understand. Felton's says I need 1 four inch air inlet. Is that enough? Th chimney size says 3 in at a length of 27 inches. Is that enough? Should the chimney be mounted at the cooking grate level or higher?
post #12 of 36

Take a look at the firebox vents on this build: http://www.smokingmeatforums.com/t/144907/m7s-build-thread-reverse-flow-trailer-mounted-with-storage-compartments/60#post_1205328

You would be well served to add an additional inlet slightly above the fire to move the heat through the cook chamber. You can make the inlets round, square or rectangles as long as they have the required area, then you can add a smaller one up higher to really help move the air. As far as the chimney, 3" is a good size for your cook chamber and the length should be around 30" above the top of cook chamber, there is footnote on the Feldon's page about chimney height that says they should be 30-40 inches.


Height above cook grates can become an issue of religion, some say put it at the grate, and some say the top of the cook chamber to keep the smoke from getting stale. The link above has an interesting twist, earlier in his build you can see he used both and then added dampers on the chimneys so he can adjust the amount of smoke that exits from either level of the cook chamber, very clever but I don't think he has had a chance to play with them yet to offer results. On your diameter, you shouldn't have too much of a thermal stack with varying temperature within the smoker so you can put it at the top and always put something inside to lower it if you don't like the results.


Hope this helps and keep us posted on your progress!



post #13 of 36
Thread Starter 
Thinking about adding a warming box above the firebox. Any opinions on if this is a good idea or not?
post #14 of 36

I personally have no use for one, however I can see where cooking for a large crowd or catering might present a situation where it would be useful if you must hold some items at temp, or to rest, while others go on the smoker or finish up, so that service can begin at a specific time.

So the answer really depends on how you expect to use it.

Just cooking for the family as I do, it is not really needed.

If you have higher aspirations, you might find it worthwhile.

post #15 of 36
Thread Starter 
I have started the build with the 36 in tank. After cutting the lid yesterday we noticed some kind of blue coating on the inside. The tank is a 30+ year old tank. Any idea of what this coating? Should I scrap and find another tank?
post #16 of 36

Put a torch on it and see if it comes off easily, don't heat the CC up enough to cause warping, just see if it will peel. If so, it will be easy to remove with a cup brush after burning out the CC with a wood fire. Most normal paints will give it up @ less than 350 degrees.

post #17 of 36
Thread Starter 
So if I torch it and nothing happens just go forward with the build? I am being told it may some kind of epoxy and the fumes that could be there concern me. A paint store said to just paint over it with high temp paint and it should be fine.
post #18 of 36

Any paint on the inside should be removed, not painted over.... as we say in the south, "Bless their hearts".... Most epoxies are not that bad to remove since they break down in the 300 degree range. You need to get it off no matter what and it should not be a problem, if you search the forum you will find several posts on burning a fire in the CC to remove paint.

post #19 of 36
Thread Starter 
I probably just need to scrap the tank?
post #20 of 36

Put a torch on it and see if it comes off easily, don't heat the CC up enough to cause warping, just see if it will peel. If so, it will be easy to remove with a cup brush after burning out the CC with a wood fire. Most normal paints will give it up @ less than 350 degrees.


Go outside and give this a try and let us know how it worked out.

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