Reverse Flow Build Question

[Bigfork]

Greetings Forum!
I haven't posted here in a few years... that said, I still ghost about, gleaning information as needed:wink:.


This is my second RF build. The first one had over a 10k cubic in cook chamber and gobbled a bag and a half of briquettes for a 8 hour smoke. It works great but is crazy overkill for the Mrs, pipsqueak, and myself.

Enter my 2nd build. Smaller, more efficient, less charcoal= less work.
The picture shows the first test fire. It obviously needs a rolling stand (tripod style), a sandblast, and a finish paint.
Here's my numbers:
Fire Box (FB) 12x12 cylinder
Cook Chamber (CC) 18x14.5 cylinder (CC little smaller than the recommended FB to CC ratio. I'm not worried about it. Slightly small CC-FB is better than too big)

I used the Feldon's Pit Calculator to conjure up my numbers.


So the results: The thing rocks! Much less coals to keep steady temps. I do have one question for the community. The calculator said if I use 2" tube stock for chimney, it needs to be 21.6 inches long. You can see the chimney in the pic. So during the two test fires I've done, I was achieving proper temps (pushed it to 350F to burn off crap) but at all temps, there is a large amount of smoke sneaking out around the door to the CC. The door is the best 'sealed' door I've done on a smoker, very tight fitting with ban-saw blade as seal overlap. The door fits as good as one can without being watertight.



I have the funny feeling the 90 degree turn in the chimney and the 2" dia are constricting to the chimney out-flow even though I used Feldon's Pit Calculator.



The chimney is offset from CC center-line with the idea that If I had to, I could add a second one next to it... like a double barrel shotgun. I could then dampen the exit(s) if it is too much out-flow.


Perhaps my CC lid isn't as sealed as I think. Should I do the high temp silicon bead around the door before adding a second chimney?



What do you think?
If the CC is constantly leaking smoke out of the door, is chimney flow the logical issue? Should I add a second 2"dia x 21.6" stack?

thanks for the comments!!
cheers.
What do you think?
If the CC is constantly leaking smoke out of the door, is chimney flow the logical issue? Should I add a second 2" stack?

thanks for the comments!!
cheers.

 

[SmittyJonz]

Why did you build an offset for charcoal ?

 

[Bigfork]

chimney size

Are you saying all RF smokers should be just sticks? I was under the assumption that charcoal provided a more even and controllable heat(?) and the sticks are for flavor (smoke).



My big build, a 10k cu inch CC, might behave well as a stick burner, but the one I've just built is quite small. The FB is a small propane tank with a "coal sled" that slides in and out.



I did another test fire last night but a couple hours before, I used high temp silicone around the CC opening, Vaseline as a releasing agent against the lid. This had a profound effect! Very little smoke escaping from the CC now! I guess my lid was not as tight sealing as I thought:wink:.



That said, I still feel like the 2" dia 21.6" tall (as per Feldon's Pit Calculator) chimney is too restrictive to outflow...


Because this RF smoker is so small, I wonder if at some point, Feldon's calculator might be giving me improper data...related to chimney.
Hmmm
thoughts?
Anyone else have a small RF with a small dia chimney?


thanks!

 

[Sid Post]

I don't think the calculator is optimal for small cookers like this one.

As you noted, I think you are basically in the WSM size class so charcoal makes a lot more sense then it does for a bigger smoker. Personally, with a small smoker like that, I'd try to run sticks most of the time.

I suspect your 2" chamber opening is too small. If it were mine, I do a Texas-style slot at grate level with the straight piece of pipe in the top of it.

 

[Bigfork]

Thanks Sidpost.

I'm gonna fab up another chimney and turn it into a double barrel. I'm quite sure the 2" pipe, even though it's recommended length, is too little draft. I can install a second fairly easily and then dampen if it's too much up draft.

Nothing else to do other than play in the yard!
cheers.

 

[Pete Mazz]

2" is too restrictive

 

[Sid Post]

Your welcome! :-D

Take a look at Johnson Smokers in Texas. He uses double smokestacks and gets very favorable comments.

https://johnsonsmokers.com/compact-patio/

I like the looks of the classic Texas-style pipe smokers and the grate level slot for draft works well and is easy to control with a simple damper like you see on my Evie Mae. In the end, there are many different ways to get a good result so have fun with the mods!

 

[Nuco59]

I think the calculators are out the window on something this small. Could be the 2" diameter stack is ok but it's way too tall at 21" /shrug. It's your time and your toy- play with it all you like. I'm interested in where it takes you. I don't know how many "usable" square inches of grate you can get out of it- the reverse flow might help you some- but I'd think the inches right next to the fire box would get too hot.

I had a couple of small tanks up at work for something like this - a freon sized tank and one about twice as big. Figured it'd be a good welding project but never did it. I sort of decided against it when I determined my miniwsm would hold more food and be a far better cooker...

There IS a 60 gallon air compressor tank that I have my eye on. I put my name on it for when it gets retired... that size would make a fine back yard cooker- not too big- not too small- just right. (for me anyway)

 

[Bigfork]

Results!

Well an update is due. I forgot to take a picture of the ribs I was so excited.



Draft out was the issue. I added 2nd 2" pipe, same 21" length... Now she blows properly, moving plenty of smoke out. At about 220* F the maple white smoke turns to sweet transparent torch.



And I like the look :wink:. The old double barrel. coals lasted 2.5 hours between refills. Big pork rips for 7 hours total. Seems really efficient compared to my huge one. This thing will get some use.



I'm tickled. I know what I'll be doing (while I sit about my house waiting for the virus to blow over...)


I'm super stoked! Now for legs, wheels, sandblast, and paint.


Thanks for the thoughts gang!
bigfork