Rectangular RF Smoker from Holland (Europe)

[Dutch_Erik]

Hi all! As posted in Roll Call, I'm planning to build an offset, reverse flow smoker. This'll be a family project for me and my dad. Neither of us currently knows how to weld, so that's the first step in what will surely be a great project.

Meanwhile, I am working on the design. As stated in the title, this will be a rectangular, offset, reverse flow smoker. The choice for rectangular is based on personal taste and local availability of materials.

Using the excellent tutorial on this forum, I have come up with the following dimensions (pardon the metric system):

• Cooking chamber dimensions: 120cm x 50cm x 50cm = 300 liters = 18307 in3
• Minimum firebox volume (above the grate): 300 * 0.33 = 100 litres
• RF channel area (oversized by 30% due to small cooker volume) = 18310 * 0.004 * 1.3 = 95 in2 = 620cm2
• RF channel height = 620cm2 / 50cm (cooker depth) = 12.4 cm minimal height
• Exhaust stack volume (above CC) = 18310 * 0.022 (oversized 30%) = 403in3 = 6.6 litres
• Exhaust stack optimal height = 36" = 91cm
• Exhaust stack dimensions: height (above CC) = 85cm, diameter = 10cm (i.d.), volume = 6.7 litres

If anyone has a spare moment, please check if my calculations are correct. I tried to convert most things between metric and US units for easier reading...

One question I already have now; would it hurt or help to take the stack to exactly 36", making it approximately 10% oversized (on top of the +30% already incorporated for the lower volume)?

Thanks for reading :)

 

[ahumadora]

hi. Metric is no problem for me. Always better to er on the side of bigger if in doubt. Especially with a small cooker.
A local sheet metal place should be able to cut and bend what you need.

 

[Dutch_Erik]

hi. Metric is no problem for me. Always better to er on the side of bigger if in doubt. Especially with a small cooker.
A local sheet metal place should be able to cut and bend what you need.

Thanks for the feedback :) what do you think of the dimensions I posted?

 

[daveomak]

May I suggest, you convert all of your metric numbers to inches and then run the numbers... I'm getting some discrepancy in the numbers..

 

[Dutch_Erik]

May I suggest, you convert all of your metric numbers to inches and then run the numbers... I'm getting some discrepancy in the numbers..

Ok, here goes:

• Cooking chamber dimensions: 47.17" x 19.7" x 19.7" = 18307 cubic inch (in3)
• Minimum firebox volume (above the grate): 18307 * 0.33 = 6041 in3
• RF channel area (oversized by 30% due to small cooker volume) = 18310 * 0.004 * 1.3 = 95 sq. inch (in2)
• RF channel height = 95 in2 / 19.7" (cooker depth) = 4.8" minimal height
• Exhaust stack volume (above CC) = 18310 * 0.022 (oversized 30%) = 403in3
• Exhaust stack optimal height = 36"
• Exhaust stack dimensions: height (above CC) = 33", diameter = 4" (i.d.), volume = 415 in3

Thanks for reading :)

 

[daveomak]

Diameter X Diameter X 0.7854 X Length = Volume in cubic inches

I come up with....
19.7 X 19.7 X 0.7854 X 47.17 = 14,378 cu. in.

I don't know where you are going wrong ????

 

[Dutch_Erik]

Aaah, hang on, I see what's happening here ;) I'm building a rectangular smoker, not a round one.
Therefore I am calculating volume by multiplying width x depth x height.

 

[daveomak]

Without going through the other numbers, I'm going to say you've got it...

 

[Rings Я Us]

I hope to see this thing in action by summer. :)

Good luck.

 

[Dutch_Erik]

Without going through the other numbers, I'm going to say you've got it...

Thanks for your assistance :)

I hope to see this thing in action by summer. :)

Good luck.

Thanks, that's the plan :)

 

[Rings Я Us]

Aaah, hang on, I see what's happening here ;) I'm building a rectangular smoker, not a round one.
Therefore I am calculating volume by multiplying width x depth x height.

Check out this guys work. Looks nice. He used some plans from another guy in here that built one..
https://www.smokingmeatforums.com/threads/vertical-insulated-reverse-flow-smoker.257839/

 

[Dutch_Erik]

So, the build will end up looking vaguely similar to this: (image off google)

Still horizontal, but with a rectangular cooking chamber and firebox. Reason for this is because large pipes and/or propane tanks are not a common sight over here, so sheet metal is easier to source.

 

[Rings Я Us]

That will be a great project. Looks cool.

Clover ridge smokers . Nice
http://www.stickburnermafia.com/clover-ridge-smokers/

Only thing is, You have to open both doors to check one thing on one shelf.

 

[Dutch_Erik]

Only thing is, You have to open both doors to check one thing on one shelf

Which is exactly why mine will have 2 horizontally split doors :D

 

[Dutch_Erik]

So, the rough design is finished :) pics below...

Please let me know what you think :)

 

[daveomak]

Weld-R-Up....

 

[ahumadora]

I would shorten the stack a little. Looks long and thin in the sketch. It will draw fine being a little shorter.

 

[Dutch_Erik]

I would shorten the stack a little. Looks long and thin in the sketch. It will draw fine being a little shorter.

Currently it's pretty close to the recommended 36" above the CC. It's 90x90mm outside dimension, 4mm wall thickness.

I calculated the difference in internal surface area between a round and square pipe, and increased the internal volume of the stack by 15% to compensate for the extra friction loss.

 

[ahumadora]

You can buy steel in 90x90mm in Holland? Personally I would use 100x100 and 3.2mm (1/8) is plenty for a stack. Your firebox is mounted low and is a tall shape already so you will have good natural air flow through the smoker as well. my 2 cents.

 

[Dutch_Erik]

You can buy steel in 90x90mm in Holland?

This comment made me double-check my measurements, turns out there was a mistake in the calculations somewhere!
A 100x100mm stack is the minimum needed, which would come to roughly the same height as the sketch shows. Next bigger option is 120x120mm...

Thanks for the input :)