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need help with my reverse flow design please

post #1 of 23
Thread Starter 
Hi im from england and had not heard of smokers untill recently never seen one dont know anyone who has. I work as a welder and was making a barrel bbq out off stainless 16" pipe until I came across bbq smokers online. Now I really want one lol.

Iv done a bit or research which is how I came across this gold mine of a forum and think I want to make an offset reverse flow smoker.

Do I need a heat deflector

im unsure how to fo about a baffle plate. Do I need to put holes in it that start off small firebox side then get bigger as I get to the opposite side?

Should I cut a drainhole under the baffel plate to remove fat or make a drip tray above baffle leading to a hole in the side of the cooking chamber with an outlet valve.

as I was making a barrel style bbq iv cut the pipe im using in half. Will weld it back together but thought it would be easier to fit baffel etc first.

Sorry this is a bit longwinded but iv got so many questions and no one to ask.

heres some pics off the scrap material im hope to use. Its all stainless hope not to have to buy anything apart from temp gauges


post #2 of 23
Thread Starter 

dimensions are 16" diameter by 33.5 inch hopeing ro make a fire box from some 14" pipe cut at 16" long.
post #3 of 23

I don't know where you are; however, send this guy a private message. He is at least on your side of the pond and may be close enough for you to review his work in person!




We will be happy to lend a hand with your smoker planning. I will be along later this evening to give a more detailed response. In the meantime, read this thread for insight into the calculator many use to layout the design.




The calculator shows both offset as well as reverse flow.

post #4 of 23
Thread Starter 
Wow thats a nice smoker its massive lol.

Iv only got a rough idea of how I want to make it completely open to suggestions.

currently the body of my cooking chamber is going to be a piece of stainless 16"pipe cut at 33.5" with some 6mm plate welded to the side.will stainless work as well as carbon steel for a smoker? Id like to make the whole project from it as iv collected a lot of stainless scrap. I know reverse flow would work better with domed ends so I may weld some segments of pipe at bottom and top to try and improve flow. Wont bother if you guys think its unnecessary.

iv got a 2big sheets of stainless 1is 3mm the other is6mm uunsure what to use for baffle plate also unsure of baffle height from bottom of the cooking chamber and how far from the end of the cc the baffle should stop. Iv done a drawing of some of the info im after it shows dimensions for both cc and fb its a bit rough lol.
id really appreciate any help you guys can give me.
post #5 of 23

Hello bearface.  Back when I built these things we did it by experience/trial and error.  I can tell you you want the grease drain at the end where you have the gap for the baffle plate.  I could give you my opinions but seems now a days there is a "calculator" that answers all these questions for you.  I happen to know a member who is a WIZZ at that calculator and he builds some really fine smokers.  I have built a few in my time and I can tell you the man knows his stuff!  I have asked him to have a look and offer his advice.  I will see how far off my ideas were.  We will learn together.  Keep Smokin!


post #6 of 23

Here is a link to your smoker in the calculator. If you read the links I provided above, it explains the calculator.




You will want the height of the cutout on the 16" pipe to be around 3.5 inches which yields an segment area of about 32 square inches. You want to mount a solid, no holes, (6mm) reverse flow plate at that same height all the way across the cook chamber and leave a rectangle opening of at least 32 square inches, so 2-3 inches @ 16 inches wide will suffice.


Instead of baffle plate, they are usually referred to as an reverse flow (RF) plate. Usually at least 1/4 inch in thickness and you would mount your drilled plate grate about 4-6 inches above that. Looking at your smoker diameter, you can mount the cooking grate at the middle of the pipe.


Hope this helps!


post #7 of 23
Thread Starter 
Len your a star thankyou so much mate. That link even gave me a chimney size dead handy for an amateur like me. Iv cut the rf plate now so excited to be underway

I hope to plaz cut the link between cc and fb in work tomorrow.

is the drilled plate grate the same thing as cooking grill? Or is it for distributing the smoke? Do I need one for the smoker to work correctly. Sorry if these seem like dumb ass questions but im totally clueless.

Was thinking of cutting the rf plate in half and putting a slight fall off less than 1/64 maybe 2or3mm into the middle and having a waste pipe there. Also do as danny said and put one bellow the gap into cc.

post #8 of 23

On the drilled plate, I saw the picture of the plate you had that was drilled. I have a friend that uses one of those for his cooking surface mounted above the RF plate by about 5". He reported that it works very well since it is thicker than most mesh allowing it to hold more even heat. The smoke will be able to circulate like a wire mesh or rod cooking grate but hold heat better.


Make sure to go ahead and run that chimney up around 30" above the cook chamber, it will draw better at that length. 


I have seen the fat drain done several ways. Some guys split it along the length and put in a piece of angle iron to act as a trough and dam off the end with a hole to a pipe out the bottom of the cook chamber. I've seen guys also put a dam at the far end from the fire box and and put the pipe out the bottom of the cook chamber and just adjust the level of the whole cooker so it will drain towards that end, it won't take much. Browse around some of the threads in the reverse flow build section and you will see several options and use one that you think will work best for you and the hardware you have laying about. Check out post #27 on this build. http://www.smokingmeatforums.com/t/167402/first-time-build-250-gallon-propane-tank/20


Always glad to help, if I ever get over there, we'll have a pint!



post #9 of 23

Cook Chamber 6,736 Cu In   16" x 33.5"   


Fire Box    14" x 16"   round  2,463 cu. in.  110 % of recommended     That size will work fine also can go a little bigger if you want


FB to CC opening  26.9 sq in     a to b  14" (your FB Pipe)    C should be 3"





Stack   3 " needs to be 16 1/4"  4" needs to be 12 "   This is round pipe



LOW  -----     FB Openings  7.21 cu. in recommended   3 ea   1 3/4" round holes  



High (across from FB to CC opening    1.35 sq. in  recommended --   3 ea.  3/4 inch holes



Area under RF plate   same as FB to CC opening



I have seen drains like you have proposed they work well, I made my RF plates two pieces with beveled edges so I can remove them, My drain is located in the bottom of the Cook Chamber



Hope this helps



post #10 of 23
Thread Starter 
Been a busy few months for me with a new baby he's 9months now so iv got a little bit more time to myself and have started work on the smoker again.

Just put a temporary handle on cc for now. I'm looking to start fab on cc door seal. Unsure what gauge plate to use it have several sheets off 3mm 1/8th plate
Or I have some unistrutt that is 2mm
Have plenty of 1/4" if that would be better.
Should I weld it on from the outside on top of cc or the underside of door from Inside?
post #11 of 23
Thread Starter 
Also think iv messed up the opening from cc to fire box. Sorry Gary for some stupid reason iv cut out a half moon shape. On your diagram it shows 3" from C iv done 3 1/4 inches from bottom of cc to top of cut.
A nightmare if this needs to be bigger as iv cut and tack welded baffle in place
I think it may need to be smaller as on feldons chart it says I need a diameter of 6.76" and I have 12"
post #12 of 23
Thread Starter 
I have enough plate to make a square box so will keep the half moon shape

So I hope to just weld a strip in this to reduce diameter down to 6.7".
Any help would be really appreciated As im not sure if I do need to make it that small or not. Thought I was on to a winner until I Re read Garys post and saw his diagram what a plank I am
post #13 of 23
Originally Posted by bearface View Post

I have enough plate to make a square box so will keep the half moon shape

So I hope to just weld a strip in this to reduce diameter down to 6.7".
Any help would be really appreciated As im not sure if I do need to make it that small or not. Thought I was on to a winner until I Re read Garys post and saw his diagram what a plank I am

If you are NOT using the football shape opening now, you need to recalculate the size of the opening and forget the football dimensions......
post #14 of 23
Thread Starter 
Hi dave cheers for replying mate. I'm getting well confused. iv followed the link on this post to feldons page
By half moon does it mean a semi circle? I was hoping to put a semi circle in the cc
post #15 of 23
Thread Starter 
Think the penny has dropped now mate.I will try and make the area between fb and cc 18 square ". Which is good because easier to lower baffle than weld more on to raise
post #16 of 23



This is the link you should use to do the calculations, read the full posting and do the calculations in the first post. There are problems with Feldon's when used for reverse flow that are explained fully in the body of the text.


This should clear things up for the opening areas.



post #17 of 23
Thread Starter 
Cheers len just used this and must admit I thought when I first saw it id never make it work but fair play to dave it's really easy to use. step by step instructions no problems. Really impressive.
I fine tuned my dimensions and did calculations based on 16" pipe 33" long and it told me opening had to be 26.54 cubic inch.
When I followed the link I put 8" diameter and crossed my fingers and put 3.1" for the segment height as this is the height already cut in to the cc.
It told me that the segmental area was 27.35
Can't believe how close these two are. Do you think that will be OK as it is?
Thanks so much for your help I'm feeling really positive about this build again now especially with daves calculator for guidance.
post #18 of 23
Close enough.... You are good to go.....
post #19 of 23
Thread Starter 
Thanks a lot dave was panicking for a while. Can't belive how lucky that turned out! Can build my fire box this weekend rather than go backwards fixing my mistake

Iv got two pieces of 20"x20" 10mm (half inch I think) plate to use on fire box and similar amount of 1/4" plate. Was wondering Where would be best to use thicker plate to help with heat loss. Assuming the top of the box for one piece as hot air rises thinking maybe back or bottom for other bit. Not sure if it really matters but would be a shame if It could have been put to good use.
post #20 of 23
To help reduce heat loss out the top plate, a heat shield plate would help... also helps with the RF plate getting too hot just next to the FB.... It can be extended into the CC or where ever you want it....

...click on pic to enlarge....
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