Blakes (Newby) Offset smoker build

[Blizzo]

Hey team. Blakehere from what is most likely a long way away from all of you, New Zealand (i'm struggling converting all your imperial measurements in my head!)

Ive been wanting to try low n slow bbq for a while and was about to buy an OK Joe, but they are super expensive here in NZ and thought shit im pretty good and welding and fab work ill just make one.

So I called past an engineer mates yard and picked up this -


Its appx 41" long and 16" in diameter. The wall thickness is bloody thick, around 10mm so i guess that makes it about 3/8"


One I pop that middle piece out of this end outlet it will give me just over a 3" hole which should work alright for the smoke stack, my calcs using 0.2% of the CC puts it at around 23-24 inches long for the stack.

Bonus is it comes with some cool patina which seems to be trendy these days, dumb thing is its pretty oily inside, so ill have to burn the shit out our that.


I've got some cool cast iron vintage wagon wheels on the way, and will grab some steel for legs next week.

I just need some help with design now, unless i can find some suitable pipe ill probs go for a square firebox as i can draw it up and have it laser cut which makes life easy. what size would everyone reccomend? ive looked at the calculators (feldon) but most people seem to say to steer clear from it these days. Id like to incorporate a cowboy grill with the firebox for reverse searing steak and what not. Im not too sure on the firebox size, inlet size and size of the gap from the firebox to the CC. Any help with all this would be greatly appreciated!
Cheers

 

[JLeonard]

Welcome Blake. daveomak is the go to guy for all your questions. He could write a book on it.
Jim

 

[daveomak]

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

 

[Blizzo]

cheers guys, these calculators are all for reverse flow offsets. i was planning on doing a traditional flow and copying the heat deflector that aaron franklin puts in his backyard pits. will these calculators work just as well for traditional flow cookers?
Cheers
Blake

 

[daveomak]

Yes...

 

[Blizzo]

Roger that. Am I wrong to be going with a traditional offset design? there is such conflicting advice about reverse flow or traditional. is it purely down to personal preference? I'm new to bbq so trying to take the best advice I can. You guys seem pretty clued up and are a fan of RF so maybe ive made the wrong decision, but hen why is Aaron Franklin such a fan of traditional flow? Its not too late for me to change my design as im still collecting parts.

Anyway aside from that question Dave could you please look over my numbers for me and recommend if i should make any increases due to the smaller size of my CC/Smoker?

Inside length of CC = 39.25"
Inside Dia of CC =15.25"
Inside Radius of CC = 7.625"
Internal volume of CC =716.466 Cubic Inches
Internal volume of CC = 31.067 US Gallons
Desired FB/CC Opening = 28.7 Square inches
For a 13.75" dia circle (leaves an edge for a grease dam) , to achieve 28.7 si height from bottom of circle = 3.42"
Minimum FB Volume = 2,368.23 Square inches
Air inlet = 7.18 Square inches (20% above grate, 80% below)
Desired Stack volume above CC = 157.9 Square inches
For 3" ID Stack, stack height above CC = 23"

I picked up this old cart today with some vintage 400mm dia cast iron wagon wheels on it. They should look pretty cool on the smoker!


Cheers
Blake

 

[daveomak]

You want the exhaust stack to be ~35" above the CC... That's needed for a correct draw through the smoker... And perhaps, go with a 4" exhaust stack... Building a "smallish" smoker, some liberties need to be taken.....

 

[BrisketDude]

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

I've seen this design mentioned here several times, where there's an auxiliary air intake above the fire in the firebox, but I hardly ever see it in commercial offsets. Why is that? And how would the smoker run differently without it?

Thanks
-Mark

 

[daveomak]

The folks here actually USE the smokers they build and try and make improvements as needed..
The improvement in the smoker design comes from many years of use, beer drinking and contemplating, "What can I do to improve the temperature control of my smoker while reducing fuel consumption" while sitting in a lawn chair and watching brisket and pork butt cook.... HAHAHA...

Without it, the only air flow control you have ALSO feeds more air to the fire... More heat...
The upper air inlet helps you control the temperature in the cooking chamber and the added air helps to consume creosote...
It also reduces fuel consumption by moving extra heat from the FB to the CC...

 

[daveomak]

Short/Fat 120 Gallon Build

Had a great day today! After doing a couple small little jobs on the smoker I decided to fire it up. I started with a chimney of charcoal. Once that was going I added 3 small splits of wood. It came up to 200 and just stayed there. They were small so I added 2 more and closed my intake about...

www.smokingmeatforums.com

txsmokedlk

Thought I would drop in and say how much I’m enjoying my smoker. It only took me 6 years, many life changes.
thank you for your input.
It holds heat well, hot spots are managed easy with the top vent in the door. I can maintain temps pretty good.....still learning.
but most of all I’m proud of this. Lots of history and one day maybe my son will love it too.
This smoker design works better than I imaged.
Thank you all for the help.

 

[daveomak]

Designs that work very well....



.....

 

[BrisketDude]

Hmmm. That makes sense, since if the CC is too hot, I open the door. I figured I was letting the heat out and reducing the draft into the smoker (less heat flow) but introducing cold air into the draft would work too. I'm also struggling to make things like chicken without a black residue, so maybe...

I wonder if there's a way I could test this without cutting holes in my smoker? I have a fan-assist port on the bottom. Maybe I could plumb up a pipe around & have air dump in right where the vent would be?

This is a LoneStarGrillz. The top port is a gas assist, the bottom one is for a fan. It comes out below the grate.

 

[daveomak]

That black residue is probably creosote... Drill 3 each 1" holes directly across from the FB/CC opening... OR, get electric conduit plugs and drill the holes to match.. Then you can plug them...
If you are opening the FB door, I guarantee you will like the modification.... use a hole saw to drill the holes... or a step drill....

 

[chp]

Designs that work very well....



View attachment 474927.....View attachment 474928

Do you ever see this intake become an exhaust? I’m trying to understand this idea, but it seems like it would be an easy way for the firebox to exhaust.

 

[daveomak]

Only when the smoker is a poor design..... Physics would say it can't act as exhaust...

 

[daveomak]

B BrisketDude .... One note on drilling the holes....
The gap between the holes MUST be greater than the diameter of the holes.....
That will allow for a sliding adjuster to work properly....
To make the sliding damper, place a steel plate, can be very thin, over the drilled holes.... without moving it, from the inside, trace the holes on the plate... a simple design that works very well...

 

[chp]

Only when the smoker is a poor design..... Physics would say it can't act as exhaust...

So the assumption is that the designed exhaust is high enough and large enough that it creates a very low pressure path for the fire and the intake is low enough and small enough to provide air intake. However, a second intake above and close to the pressure of the fire will certainly help meet the air needs of the fire, but if the lower intake was already designed to meet that need, it seems like that the upper opening could compete as a low pressure path and become an exhaust. I understand the designed outlet should still be lower and remain the exhaust...but I am still missing the advantage of a high intake. The only reason air is drawn in...is to meet the need of the fire, which means it still follows the same flow path. Is it the better air control that provides advantage?

 

[daveomak]

The high intake is so the air that enters there does NOT stoke the fire and increase the temperature in the FB.... The lower air inlet does that and can be independently adjusted..,.

 

[Blizzo]

The high intake is so the air that enters there does NOT stoke the fire and increase the temperature in the FB.... The lower air inlet does that and can be independently adjusted..,.

What i take from this is the there will be considerable draw if the smoker is designed well, so the stack is still by far the path of less resistance for airflow, so the high inlet would not exhaust. it may for so for a few seconds when the fire is first lit before it starts drawing.
The addition of the high vent provides extra fresh air which is drawn directly into the CC (not feeding the fire) when the smoker is running well and considerable draw is present. this will add essentially cool air to the CC and help lower the temp. I figure the people here that run this type of set up like it for fine tuning or quickly adjusting CC temp without the "swings" of altering the output of the fire

 

[Blizzo]

im still playing with the design of my smoker and struggling to come up with a concrete plan, there are just so many options! im still looking at the options of RF or traditional. i was first looking at aaron franklins design of traditional backyard smokers but now im looking at the Jambo design where the heat/smoke from the firebox enters above the cooking grate, then exits level /below the cooking grate. Do any of you think there will be an issue with this design with my small 16x40" CC?

Im also now looking at the option of insulating my firebox. do yall think this is a worth the trouble for a small smoker? or just use thick 3/8t steel like the CC?
Cheers
Blake