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300 gallon Reverse Flow Build *Need Help Figuring some Dimensions Out"

post #1 of 16
Thread Starter 

I  will be starting my first trailor smoker build this week.  I have a 300 gallon round tank that I will be using.  I have read lots of threads on here and used a few different calculators.  I need some help figuring out:


a) what size firebox to build

b) what size flu to build

c) what size gap to have in the reverse flow plate


My design will have two racks in the smoker that pull out.  One at the half way point and one a little higher.  Here is a pic of the tank I got.  I posted it in the side fire box forum, and cant figure out how to delete......Mods help???? :)


Thanks for your help


round tank.jpg

post #2 of 16

if you can post some dimensions i can help you. need the diameter of you tank and the length. also if you have any idea what type of fire box you want-square or round, and any starter numbers if any... like if you have another tank you want to use or something.

post #3 of 16

do you have any idea what size pipe or tubing you have available for your stack? i would try for 6" if you can.

post #4 of 16
Thread Starter 

Duck - thanks for responding.  The round tank is 38" across and 61" long.  I did call a buddy that runs a mufler shop.  I am going to use a 6" aluminized pipe for the exhaust.  I did hit a major score today.  I picked up a square metal diesel 120 gallon fuel tank for $10.  I will post the diminsions tomorrow as I dont have them with me.  I need to find a square metal charcoal stand up smoker chamber.  I want to use this to sit on top of the firebox as a warming chamber and cut a hole in the bottom and install a damper to let a little heat in.  I figure they are $40 at menards new, and that will have the racks, door hardware, temp gauge, dampers, and waterpan already in it.  Just have to weld it to the firebox,  also thinking about running the 6" exhaust through the warming chamber and out the top since I want to keep it tight to the chamber and fire box.  Does anyone know if you can get high temp paint in colors?  One daughter thinks it should be a Yankee smoker, and the other thinks it needs to be a Packers smoker :)

post #5 of 16
Thread Starter 

I am thinking of a warming box on top of the firebox.  I want to mount a empty keg on top of the firebox and cut a door out of the front, flu with a damper in between the two boxes to control temps, and a small damper and stack out the top.  Would love a place to keep things warm, or even cook potatoes or sweet corn, or warmup buns.  Thoughts???? 

post #6 of 16
Thread Starter 
The measurements on the firebox are 49x24x24. big of an opening do you think I need going into the smoking chamber? I need to figure out what length of pipe I need for two 4" stacks as opposed to one 6". The 6" they can't bend and I don't want to use fittings so that I can keep it right up against the smoker.
post #7 of 16

sorry ballagh! i've been away from my computer for a while. i will answer your questions hopefully tonight. i'm at work now or i would do it now.  

post #8 of 16



I used the calc.  Based on the dimensions that you gave:


1. the firebox volume needs to be at least 23,049 cu. in. ( your firebox is 28,224) so you are good with that.

2. the opening from the firebox to the cooking chamber needs to be at least 225.79 sq. in.

3. the firebox air inlet 84.67 sq. in.

4. the Exhaust Chimney volume 1411.20  So with two pipes you just need to meet that volume.


Based on the input I received from the forum members while building a smoker all of the measurements are very important.  I followed them pretty darn close and the smoker turned out great.


Good luck and let me know w/ qview how it turns out!

Oh ya.. I used DODIS' BBQ smoker ratio calc.

post #9 of 16

Ballagh, Good luck on your build. as to your question: what size gap to have in the reverse flow plate. I'm thinking you're asking about the gap between the reverse flow plate and the end wall of the tank? The distance between the plate and the wall of my Lang is about 6 inches wide. The cooking chamber of my Lang is 60 inches wide and your tank is only an inch wider so I think you would be good to go with a 6 inch gap.

post #10 of 16

I think a rule of thumb is the gap square inches should equal your opening at the firebox.

post #11 of 16

MattS is correct.  The volume should be the same for both openings.

post #12 of 16
Thread Starter 
So I should be good with a 6" gap between both the reverse flow plate horizantally at the end gap, and the gap where the firebox smoke enters the smoking chamber. Cool. I am going to stick as close to the measurements as I can, being this is my first build. I appreciate all your help and input.

Ok one other question :)
Hinges. Piano style the way to go, homemade, or a 6" SS from a online store?
post #13 of 16

well, i have come up with a new addition to the baffle plate gap thing.... what if it was adjustable?! (i haven't seen this done yet)

i made an adjustable plate for the end of the baffle plate. i have heard 2 different schools of thought on how big the gap should be;

  1. the gap at the end of the plate should equal the square inches of the space under the plate. which would be slightly bigger than the firebox to cookchamber opening.
  2. the gap should equal the square inches of the stack inside diameter.


i made my plate gap the size of the first option and made the damper to close to the size of the second option.


here is a pic of the damper fully open

gap full open.JPG


here is a pic of the gap closed to the minimum open position

gap closed.JPG



here is a pic of the adjustment arm

gap adjuster.JPG

post #14 of 16

Well an interesting idea,


Let us know how it works.

post #15 of 16
Thread Starter 

Here is my warming box that will be welded to the top of the firebox.  Picked it up for $20.  Going to cut a door in it and put a couple of racks in there, with a damper inbetween the two boxes and a flu out the top.  Main use for this will be baked potatoes, keeping meat warm, buns, etc...  I have another idea too,  I am thinking of spraying the other half of the firebox top with some kind of teflon, that a guy could cook bacon, and pancakes on.    for those early morning smokes :)  Think it would work?


I also picked up a piece of 1" black pipe, a 1" ball valve (for the reverse flow plate drain) and 5 - 1" caps, and 5 1"x2" nipples to use a probe pass throughs on the front of the smoker.



post #16 of 16

This is giong to be very interesting

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