250 gal RF build

[Ziggly]

I am starting a 250 gal propane tank (30” Diameter) reverse flow build and have a few questions if some of yall don’t mind providing some help. I have read a lot on this site and others and it has been stated a couple of times that it is very difficult to build a smoker that will function correctly on the first build. This is a little disheartening considering the time money and effort involved in build one so I want to make every effort to do it right. That being said hopefully I have not already got ahead of myself on the construction, considering I already cut the tank. I have gone through Feldon’s Pit Calculator to aid in the design and I am in the process of drawing it up. I don’t think a drawing is really necessary but I thought it will help estimate steel quantities. I am going to have the plate steel cut to size by the supplier so, my first Question is about the Fire Box dimensions. I am thinking about going with 32” wide x 30” long x 24” height, this gives me about 20% more volume than the minimum suggested by the calculator. My question is about orientation of the fire box. I used the 24” as the height because the trailer clearance is low and wanted to minimize how high I need to mount the tank. My trailer is only a 36” axle so I want to keep the center of gravity as low as possible. Does anyone see a problem with these dimensions? Mainly the height, for combustion would it be better to be taller than longer?

My next question has to do with the fire box, baffle plate and rack elevations. I am thinking of putting my baffle plate 10” off the bottom of the smoker and using this as my fire box to cooking chamber elevation also. This will provide 206 sq in of opening approximately 10% greater than the minimum from the calculator. Is there any problem with the top of the fire box being the same elevation of the baffle plate or does there need to be some separation to aid in drafting?

I set 6” from the baffle plate to the first shelve so I can burn charcoal on the baffle plate and use the smoker as a large grill and I just split the difference from the bottom rack to the top of the chamber to set the top rack elevation. Does anyone have any better suggestions or comments on this layout?


My third question has to do with the shelves and shelve racks, I want them to be strong but the cheaper and lighter the better also. The largest shelve will be approximately 30” x 30”. Is an 1/8” x 1/2” angle stronger enough for the shelves and racks or do I need to go with something larger?

My last question is about the door flingers and hinges. I am planning on using 1/8” by 1 ½” for the flange. Most of the hinges I can buy (bullet/barrel hinges) would have to be welded to the flange. Is this strong enough or does anyone have any suggestions?

I know that it seems I am getting way ahead of myself and should probably focus on one task at a time but the steel supplier only sells 20’ lengths and I have to borrow a friend and a trailer to pick it up so it would be best if I can get all I need at once. Thanks for everyone’s help. This site has already been a tremendous help.

[TuscaloosaQ]

on a lot of my builds the top of the firebox is the continuation of my baffle plate but in my opinion 6 inches is to much height from the baffle plate to first grate . 4" is max for me, I understand what you are doing with the charcoal but>>>> you are going to loose some radiant heat at that distance when in the reverse flow mode. Yes the angel you described is to light for racks I go with inch and a quarter X 3/16 for tracks and either 1x1x1/4" angel for grates with 3/4 #9 wire or 1x1x11 gauge tubing with 3/4 #9 wire for my racks. The material you described for the strapping will be fine!!!!!! Are you sure 10 inches height is right going into cook chamber????? I know you are 30" od but what is the length???? Seems a little big to me if you are going all the way across for your smiley face ie cut out but I do not know the length!!!!! I buid many 250 gallon builds I will have to go back and look at my numbers

[Ziggly]

TuscaloosaQ, thanks for the advice on the metal sizing and I rack heights I certainly don’t want to sacrifice smoker performance for grilling capabilities. Should I move the baffle plate up 2 in or move the racks down. Smoker performance is more of a concern for me than cooking area. As for the fire box to opening size I just plugged the 250 gal tank size into the calculator and it suggested (184.32 sq in). Attached are the numbers I am working off of. I do plan on leaving the whole smile face cut out. I didn’t know how to calculate this Area mathematically so I laid it out in some CAD software and measured it 9 inches gives me slightly less than 184.32 and 10 gave me slightly more(206 sq in). My thought was bigger is better and I can always damper smaller but I don’t know if this is correct. I Cut the end off tank at the weld line so that left approximately 73” from the cut end to the start of the curved end. If I calculated the volume correctly I have about 225 gal of tank left. Should I update the calculator for the volume change? Do you have any thought on the fire box height? Thanks for your help.

[TuscaloosaQ]

If it were me I would prolly move the rack down 2" generally I let the top of my firebox be the continuation of the baffle plate. but id do not think it really matters that much if the inside top is a couple inches above the smiley face. I sometimes cut the end bell off on my firebox end and sometime I just make the notch on the head for the firebox. I ran your numbers with the head cut off and I come up with...157.46 with a cut 8.5" high the horizontal length being 27.037 inches. You can bigger if you want but I stick to the calculations. The numbers I just said are a little oversized 8.25 actually puts you dead on. As long as your firebox is at least equal to the pit Calc you will be fine I oversize about 5 to 10% .Hope this helps I have built many of them and have builds going on now!!!! They perform excellent!!!!!!

[Smokeone]

If TQ says it, then I would do it. He is spot on!
I too would lower my rack. Someday you may want a smidgen more room. ;)

[jwsimpleville]

If TQ says it, then I would do it. He is spot on!
I too would lower my rack. Someday you may want a smidgen more room. ;)

^^^ Yeah, go with what he said ^^^

[Ziggly]

If it were me I would prolly move the rack down 2" generally I let the top of my firebox be the continuation of the baffle plate. but id do not think it really matters that much if the inside top is a couple inches above the smiley face. I sometimes cut the end bell off on my firebox end and sometime I just make the notch on the head for the firebox. I ran your numbers with the head cut off and I come up with...157.46 with a cut 8.5" high the horizontal length being 27.037 inches. You can bigger if you want but I stick to the calculations. The numbers I just said are a little oversized 8.25 actually puts you dead on. As long as your firebox is at least equal to the pit Calc you will be fine I oversize about 5 to 10% .Hope this helps I have built many of them and have builds going on now!!!! They perform excellent!!!!!!

TQ, Thanks for your help. It’s not often you find a professional willing to share his trade secrets. I ordered my steel Friday and should pick it up today or tomorrow. I was surprised at the cost I may should of checked Bham. I have a couple more questions for you if you don’t mind and then I will leave you alone for a while. What do you think the gap should be from the end of the baffle plate to the cooking chamber and do you slope your baffle plate and if so in what direction? Thanks again.

[Frank_Cox]

your BP Gap needs to be no larger than the sq in of your throat opening. you can usually go 50% to 20% smaller than the throat opening.


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[jwsimpleville]

I heard a few times, that guy that goes by the name "Frank_Cox" knows a little about building these things so I'd prob listen to him. I think he's even built one or two himself.

[TuscaloosaQ]

If you want to you can slope your baffle plate away from your firebox. I do not worry about to much because.... most of the grease is consumed by the heat from the baffle plate. plus you can tilt your cooker a little if it is one a trailer.

[Ziggly]

Can I get some advice on the chimney from some of yall that have experience? I have been unable to locate any 6” pipe without buying a whole 21’ stick but a friend at work said he had some 8” stainless he could give me 3 feet. I updated my design with the pit calculator and the results are 22” length.

My questions are: Will there be a functional problem using a pipe this large? Is the length given by the pit calculator minimum, maximum or recommendations of exact length (should I cut the 36” down to 22”)? Can I attach the stainless to the carbon steel with my mig welder set up for carbon steel 75,25 gas?

Thanks for all the help.

[Gizmo]

Nothing wrong with using that size pipe - I've seen that big on here a few times. The calc is striving to achieve the chimney's volume - that's the important number. So just make sure you have that or just slightly over and you'll be fine. I've had no problem MIG welding stainless to mild steel - you should be good to go… imho

[Clover Ridge Smokers]

[Rodcrafter]

Sounds like you guys have him on the right track. Good job!