Horz Reverse Flow Smoker 36L 16" OD pipe build but like ideas suggestions help

LeonardK · Post by **LeonardK** » February 6th, 2019, 6:00 pm

The inspiration for this is someone saying Reverse Flow Smokers give best tasting smokey meat and Welder10s thread 16" x 37" rf smoker build, the one looks like a Red Radio Flier Wagon! It looks like an efficient economical size for singles or a family, not large groups.

16" x 37" rf smoker build by Welder10

https://smokerbuilder.com/forums/viewto ... =11&t=6031

Don't have any 48 x 18 tanks right now but a box made of 3/16 plate like to cut down for this to 38L 18D 16H.

Sometimes I like to try to put everything in one picture-plan, here it is and will pull up in a photo shop to full scale.

Made throat way over rec size, and, I really would like to hear from yall if this will work just fine, like will it make no difference.
Sloped the diverter plate 4" attached at back wall down to 2.5" over 17" leaving 1" for grease channel that slopes down from that 2.5" to cooking chamber floor... muddy figures there, I know but I'll slope a little 1" plate like that.

Never built ANYTHING before, imagining the smoke fire flow needs a channel that'll make it work not restrict flow so around diverter end is 3.5" and bottom under first rack is 3.5" and to leave something to experiment with that might make flow around food on rack better, I suggested a removable diverter plate on the left to make smoke go under the first bottom rack.

I worked with the rack spacing for a while and still I don't know what I'll cook most often, baby back ribs, pork butts, spare ribs, brisket or chicken! How tall is a pork butt?? May want to adjust a shelf to fit those...5"??

Any better suggestions on the rack space, I looked again and thought about that 4" where I imagined pulling top rack for something way over 4" tall, cooking pans for stuff like smokey mac n cheese are about 2.5" tall.

The cooking chamber size is for efficiency, so I hope I don't have to burn too much wood for a cook, would like to cook 5 times a month at least, small cooks don't need much wood.

Post something, does this plan using 3/16 cooking chamber and either 1/4" plate firebox OK ... should I go buy 3/8" plate for FB??

How about the rest, see anything wrong you would recommend different??

Leonard

Post by **Big T** » February 6th, 2019, 6:54 pm

You have to trust the numbers that the calculator gives you if you want a trouble free pit. The throat needs to be the size that the calculator recommends or you'll have major temperature issues. The BP doesn't need to be angled, I put them level front to back and end to end, there won't be a lot of grease in a cooker this size. The BP gap needs to be the same size as the throat or up to 25% smaller, the space under the BP can be larger than the throat but no any smaller. It's best to weld the BP solid so that you don't have any grease get below it. An 18'' tank will not have many options for rack spacing so you'll have to figure out how much available room you have after you install your bottom rack, 7'' spacing will allow for most large cuts of meat. The 1/4'' plate will be fine for the FB.

LeonardK · Post by **LeonardK** » February 6th, 2019, 9:00 pm

Thank You Big T

So the shape I have gives exact internal throat area of 43.5, recommended is 32, so to be sure as important as I thought flow would be and not to be restricted, I really should not be generous but exact and make it say 3 x 10.33 OR 2 x 15.36, and why is because of the velocity, opening up larger slows the flow in this cooker.

Do i really have this right?

I just didn't think that would be important here, but if it is, I'll make a diverter duct with the exact cross section throat area, thought 2" to 3" high might be about right.

30.72 sq inch calc rec area

3 x 10.33
2.5 x 12.288
2 x 15.36

Would any certain shape work better than another??????

2" would leave more vertical space in this cooker, would that work just as good as 3". I look at it again and think that a duct only 2" threatens flow, makes me think settling on 2.5 x 12.288.

I like the idea of the right size duct to insure good tight best flow. Any rule of thumb that helps make right size duct, a ratio or something?

Building this is really going to be interesting, my GF project is on hold for more money and more time. This one is for smoke intensity and the easy quick build and because I already have a box for this. Simple, no insulation just 2 boxes, stack.....etc quicker cheaper build.

Leonard

Dirtytires · Post by **Dirtytires** » February 6th, 2019, 9:26 pm

Shape is really not a concern. But if the calculator says 30.7 square inches then the opening needs to be 30.7 square inches.

Are you calling the “throat” a “diverter duct”?

LeonardK · Post by **LeonardK** » February 6th, 2019, 11:35 pm

Hi
Thank you well the exact point where the FireBox meets the Cooking Chamber I'm thinking of as exactly the throat and that connects to the diverter duct, it is a duct. Guess if I made duct different shape than connection point there would be some resistance to the flow like an eddy current ...not good

So it doesn't matter I make 3x10.33 or 2.5x12.288 ???? I rewind brushless motors for RC airplanes and stator shape ratio of Lenth to Width proportion matters some. Specially if you are really trying for most oz thrust per watt input. Thinking the 2.5x12.288 would already be distributed closer to depth of tank so no lean spots front or back where it 180s beginning of rack. I'll make it one or the other then.

Like to see this rev flo work good, my friend bought a big long used one 36" pipe 7.5 foot cook chamber, took too much wood to get it going... worked poorly. Think he's going to turn it into something else.

Kind of excited about this smaller simpler project getting it built quicker. Thank yall for your input, always welcome, might tinker some tonight and or start tomorrow

Leonard

The way we use the calculator, I see for instance someone with a 16x38 container, he put thru calculator the whole tank, not the cooking chamber minus the throat......

So you do not subtract the estimated throat size from total cooking chamber volume, just to be sure about this???? For rev flow in calculator, use the whole tank or box dimension????

LeonardK · Post by **LeonardK** » February 7th, 2019, 1:24 am

Most times designing things, I like to draw full size, and also things approaching square work better than when they get stretched, no formulas applied just that idea

So I have a better feeling about 3 x 10- 5/16" than the narrower 2.5" throat

Chromeski · Post by **Chromeski** » February 7th, 2019, 2:19 am

I'm not sure I'm understanding your question. You should be using the entire cook chamber size for your calculation whether it's a tank or some sort of box. Doing that will help get the dimensions of your firebox, throat and stack.

Dirtytires · Post by **Dirtytires** » February 7th, 2019, 4:25 pm

You don’t need a duct of any kind. For a reverse flow pit, a solid plate is welded into the bottom of the cook chamber (we call that a baffle plate). It accepts heat from the firebox thru the “throat” on one side and the heat enters the cook chamber thru the “gap” on the other side.

Your full size drawing should be one unit....I’m not understanding the 2 parts.

Have you looked at the plans that frank sells? They are really worth the investment even if you decide not to use them because they do a great job of helping you to understand how everything works. I would have never been so successful on my first build without those diagrams.

LeonardK · Post by **LeonardK** » February 10th, 2019, 1:35 pm

Here is the same thing just with some variations if this pipe is still available, two 6 foot 16" pcs $300

pipe is .375 or 3/8" thick 16" x 6 foot ID is 15.25"

Made a scale drawing full size with 36L and 12L firebox

Calculation for throat on pit calculator 17.53"
figured half for circle segment for 2 overlapping circles is 8.765 sq inches

Did half area calc on this page

https://www.mathopenref.com/segmentareaht.html

Calc from pg also in pic pipe radius 7.625" segment height 1.444" that's 2.888" for total area throat and will use a junk pc steel cut to 76.4mm to hold the center segment length while fitting

Rack 32.5 x 15 and area 487.5 sq inches or 3.385 sq ft. Looks good for an economical cooker, my old 15.25 round grill had 1.3 ft and always wanted about twice that space to cook or 2.6 ft so 3.385 sq ft sounds good.

Going to go get that pipe I think but wanted to see what yall thought about this plan AND which would give best smoke, rev flo or offset because this could easily be made into either one, just put stack on opposite side

Leonard

Post by **Pete Mazz** » February 11th, 2019, 5:55 am

LeonardK · Post by **LeonardK** » February 11th, 2019, 4:01 pm

Thank you Pete

Last night finally picked up this 16", supposed to have two pcs 6 ft, only had one left and it was 5 ft not 6. Had plans to make two 36" rev smokers that would be economical for singles or family patio cooker.

I've been drawing and working with height to see about leaving enough overhead space for a removeable rack that would stand on legs maybe leave main rack with 4.5" space and 4" top. Top rack leaving out angle on side to help smoke flow and also make 25" instead of full main width to help smoke flo.

Looking at bottom on this drawing pipe has 15.25 ID middle 7-5/8, main rack doesn't really have to slide out so I could put it even with lid cutout or slightly lower but every bit lower reduces depth, staying at center maximizes depth

How much room under the main rack should I leave for smoke flow........... OR for good smoke would the food on this rack do just as good with little or no space below main rack????? Wouldn't want to put the main too low

Just got thru working this for more room, didn't get enough pipe to use pipe also for FB so I'll use 1/4 plate for square FB something like called for 12" cubed

Making main rack a set-in instead of a slide-out with rails because it's below the lid cut and wanting to keep the lid light as possible I thought this might be a good layout making best use of the space leaving headroom for main of 7-5/8 if needed for big stuff, but if not, make a removable thin rack leaving out the 3/4 angle ends to help smoke flow and put 4 legs on that 25" rack so when removed there is no trace left of it.

I thought it might need those ends shorter for smoke flow, is that right OR NO, you would just make it same width as bottom rack?

Probably I still have to check out the throat area and see how best to make it for a round CC meeting a square FB. Calculator rec 17.53" throat. Pete, I'm trying to figure out that Dam option, OK it's a grease dam. I just thought of making a 3/8" lip on top of diverter plate that would hold grease on top and keep it out of the throat. The dam below would take more vertical space.

So is much OR any space needed under the main rack for smoke or good enough to just flow over the top of main rack?

Maybe I have some oversight, something I didn't see that you see. Thank you

Leonard

Post by **Big T** » February 11th, 2019, 5:56 pm

The normal range for the BP below the bottom rack is 2''-6'',mine are usually 3''-4''. If it's too close it'll choke off air flow and the radiant heat from the BP will cook the bottom of the meat before the top is done, too far and you won't get any of the heat from the BP. I would also recommend a taller grease damn on the BP, normal is 2'', you could probably go a little shorter if you have to but I don't think 3/8'' is enough to ensure that grease will never be able to over flow. The best shape for a square FB to round CC is a half moon to maximize the area below the BP.

LeonardK · Post by **LeonardK** » February 12th, 2019, 1:08 am

I looked and realized I posted last drwg with a pipe FB, making it out of 1/4 plate square. hope that's thick enough, that's the pipe I welded on ends.

So calculator says throat 17.53

Got to figure out what to do about that dam

Does someone have any pics of the dam like in Pete's picture, I can see the larger area above is the throat but that part below called a dam, so you put throat above and below, the grease would run down into the bottom and put a 3/4 threaded nipple to drain grease and either keep open or put valve to drain as needed.

If it was a hollow reservoir under throat it would be hard to clean, so would it be a small dammed off section about 2.5" wide with the drain there?

I'm trying to figure out grease management and can imagine things that might work, but maybe not know the best ways these are done.

Here's the 36" pipe welded, cut opening tomorrow when cold.

Thank you
Leonard

LeonardK · Post by **LeonardK** » February 12th, 2019, 1:32 am

I thought of something that would keep the height arrangements which by your Idea, Big T, 3.5" under main is in the middle of the range you like.

Grease management without losing height: put a dam on top of diverter plate/throat (in gray .5 to 5/8 tall) so it would not enter the throat at bottom. Now that red doughnut is the drain nipple slightly lower than the top of diverter plate and at that elevation on pipe might be pointing 50 degrees down. To add resistance to smoke taking that path I could 45 down and put 6" nipple that would go to metal grease bucket hung on fittings.

Would you make it a 1" drain in case of clog? Just added this idea to drwg. What do you think about how good it might work?

LeonardK · Post by **LeonardK** » February 12th, 2019, 1:45 am

Grease drain idea view from end

Post by **Pete Mazz** » February 12th, 2019, 5:05 am

On a RF the grease dam is at the end of the BP.

Dirtytires · Post by **Dirtytires** » February 12th, 2019, 11:36 pm

How are you going to fit the baffle plate in with the ends welded?

LeonardK · Post by **LeonardK** » February 13th, 2019, 12:25 pm

Hi
Well this is my first build, the GF build is needing stuff $800 worth, but this rev flo build cost less and is simpler/faster.

You know that div plate should be about 33 x 12 so it should go right in real easy thru the door I just cut. Putting hinges just now before completely cut.

: Welding hinges before door is completely cut out

Glad you asked because this kinda gives me an opportunity to again ask for some suggestions, help, or to confirm all around I got it planned/figured good.

My problem is figuring out this grease management thing, do I have a good solution? Damming and draining grease on top of diverter plate would mean smoker would need to be level or have a drain at both ends.

I do not really pretend to know, just guessing this would work good. Would yall experienced builders/users tell me if you think this plan is good or not???

I am trying to keep that vertical space, think I split the difference OK on Big Ts recommendation of having main tray within 3 to 4 ( mine 3-5/8) inches of diverter plate to get enough radiant heat for cooking/smoking.

See anything could be done better???? Please let me know. I can fit good and weld OK but this is my first smoker build.

Thank you... Leonard

Chromeski · Post by **Chromeski** » February 13th, 2019, 7:10 pm

Many guys skip the grease drain completely. If I were doing one I'd do larger than 1" pipe because that stuff gets thick and nasty. I don't think 1" is up to the task

Dirtytires · Post by **Dirtytires** » February 13th, 2019, 9:24 pm

You don’t need a drain...esp on that size smoker.

LeonardK · Post by **LeonardK** » February 14th, 2019, 12:11 am

I welded them on.... and cut them off!

Good, lid wouldn't close down right and had to weld inside anyway. So really no dam or drain for grease needed but I might just put that 5/8 dam on top edge of diverter plate to hold any excess grease but mostly it should just burn off???????????

Now it's waiting for the diverter plate, shuts right, so put that and fire box and stack and legs cart wheels.

Leonard

LeonardK · Post by **LeonardK** » February 14th, 2019, 12:22 am

Thought to add this question about stack, it pulls smoke over meat, half and half above and below main tray equally ???????

OR 2/3 above main tray and 1/3 below

OR something different????

The way I put it in plan was mostly 90% above, what do yall say is best?????

Lots people build these but never put pictures that show some of these critical things

Leonard

: Going to put a square firebox instead but what about stack placement... 50-50 or 2/3 above main tray???

LeonardK · Post by **LeonardK** » February 14th, 2019, 4:22 pm

I checked that bisector for the throat, got it wrong, fixed that, drwg is really for a 16" pipe firebox but I'm leaving that in because later I want to build one with a pipe FB

Now it's in the drawing, just about ready to go cut and weld it in there

I really thank you for the help, Lyle confirm why/how these work good and that they don't need a drain...stack at top of tray or top of cooker, Big T that thing about distance from main tray to Diverter Plate best cook between 3 to 4" so this tray will set in, not slide, but with bottom at 4.25 just flip and range is 3.5" to Div Plate

PitCalc recommends 4" stack length 8.75", takeoff = 6" add another 3 and I'm at the top of cooker

So if I wanted to make stack another foot or so higher to try to keep smoke overhead, this would be about 20"... would this be bad for performance, too much backpreasure from extra length??? Wouldn't want it too cook poorly because stack impeded flow

Thank you, Leonard

: Corrected drawing

Post by **Pete Mazz** » February 15th, 2019, 4:45 am

Stack length should be from the top of the CC.

LeonardK · Post by **LeonardK** » February 15th, 2019, 11:25 pm

So My build is 16 inch pipe 15.25 ID x 36" internal CC 6572.22 rec FB 2190.74

I am thinking this size and problem must be common enough that there are others that have tackled this question

I don't have any lifting equipment, so I have to buy this 3/8 sheet as 4x4 weight 240# hard to move too!

A long FB would be better right, long pcs of wood....

So I'm trying to get 2 fireboxes close to 2190" area using one 4' x 4' sheet of 3/8".... takes 6 pcs for each box 12 pcs total, anybody think of how to solve this??? How to cut it up... maybe I have to weld some odd pcs of same, together like I did the div plate.

Anybody have a solution/suggestion for how to cut this one sheet up, minimum of re-welded scabbed together pieces?????

A 48" x 48" sheet = 2304"

13" x 13" x 12 pieces for 2 fireboxes = 2028"

Math tells me it's possible and thinking many others like me get their steel same way, I only have 1 sheet of 3/8.

I just need top of box to meet throat with width of 12", that's all

I'm drawing and playing with numbers right now trying to get 12 pcs for 2 boxes,

does anyone have a solution, it's some kinda puzzle!!!!

also thank you Pete and Chromesky and Dirty Tires

Leonard

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