100lb Propane Build

[Marcsmith]

So, my masterbuilt propane fired smoker is on its last legs. burner area starting to rust out. on second burner, so I know it won't survive another rebuild.

I've been thinking about building a smoker for a while. a 100lb propane tank would give me a similar cooking area to the MB.

I went to feldons calculator based on common 100lb tank sizes i came up with these numbers
cook chamber 8478 ci
Firebox rec 2826 ci
i figure a 15x15x15 firebox would size which gives me a fb of 3375 ci
a 3" Dia chimney needs to be 24" tall
FB intake 10.13 sqin
and a FB to Cook opening of 27 sqin

so questions
1. is there a best space for the baffle plate, Ie x inches below first rack or X inches above FB opening

2. I was thinking of doing two racks. one at the widest point of tank, and a second rack 4" above main rack. would be a smaller rack, but would be good for thin items like ribs or brisket and could also be removed if I needed to cook a taller item, turkey, beef roast, ect.

3. i really like the propane heat aspect of the MB, predictable and fool proof. I have an old turkey fryer burner that I could utilize. I'd have to build a chip/chink tray, But also want to keep the option open for being charcoal/stick fired. thoughts?

4. Chimney. How deep into the cooking chamber do you put it. the deeper you put it the potentially more smoke that lingers. Yes?

5. does it matter where on the firebox the door is. IE can it be on the same side as the cookchamber opening.

6. can i use the top of the firebox as a "stove top" for heating sauces, or simmering items in pots?


here is a prelim sketch in cad...

 

[Marcsmith]

pretty quiet. no insight to the few questions...

so i got my tank... I've been reading up that some dawn, bleach and water rinse and repeat several times to get the Mercaptan out.

 

[daveomak]

The tutorial below will build a much better reverse flow than Feldon's.... I don't know how to adapt anything that will compare with what you are building....

https://www.smokingmeatforums.com/t...eady-to-use-rev5-6-19-15.172425/#post_1264161

...

 

[indaswamp]

Good watch for tips...
https://www.pbs.org/video/bbq-franklin-episode-4-pits/

 

[Marcsmith]

thanks Dave

haven't others built reverse flow using a 100lb propane tank? Am I setting myself up for failure?

I know that adding a propane heat option is a bit different. but I figured I could build it like a stick fired smoker, and then add the propane burner in the bottom for the heat option...just a thought. I'll run the numbers from the first page of your link. assuming that s its all manual and no spreadsheet. i saw folks talking about a file, but never saw a file posted

post #12 from gary in your post from your link above mentioned a link to formulas, but no link posted. maybe since I'm a newb the forum is restricting what I see??

i've got no problems with math, one time marine engineer...

 

[daveomak]

Just crank it by hand... Only takes 5 minutes... Calculate one line at a time... Write the answer and move to the next...
It looks confusing but one line at a time simplifies it....
If you get stuck, PM me...

 

[Marcsmith]

ok so I got my tank home. my previous guesstimates were way off. so much for all tanks being the same
LOA 43"with domed ends. volume of the rectangular cylinder 5956 in^3 domed ends calculate out to 373.3 in^3 each for a total volume of 6700 in^3 or 29 gallons so based on daves formulas

CC 6700 in^3
FB/CC opening 26.8 in^2
FB min 2211 in^3
FB air in 6.7 in^2
Ex Stack 147.4 in^3
Ex stack Dia 2.25" stack height 37" assuming 36" is ideal based on daves calcs

questions
1. RF plate- since it doubles as a drip plate, how much of a drop from high to low is common. is 1" drop on a 36" run enough? and should the low side be away from the FB

2. cooking grate- leave it on the midline for max cooking area. does it make any sense to add a second grate. it woudl be 4" above the main. 3" from the top of the smoker. would that be too close to the top too much smoke too much heat? figure it wodl be easily removable if I need to do something larger on the main grate

3 RF plate ive seen some builds where its welded in place, and some where its not. if its not welded in place then it gives you the ability to clean underneath, easily., but potentially smoke leakage defeating the purpose of reverse flow. does one clean under the RF plate?

4. FB is there any down side to going with a larger box? i was thinking a 14x14x14 box would be nice dimensions to blend well with the 14.7" dia tank.

am i overthinking...

tried to get the tank valve off. no luck. sprayed with pbblaster. let it sit...try again tomorrow

Indaswamp thanks for the vid link..

 

[indaswamp]

<thumbs up>

 

[daveomak]

I would go with 15" FB... Insert it past the weld seam.....
Increase the exhaust stack diameter to 3" ... bigger is better... Keep it the same length...

 

[smokin peachey]

Good watch for tips...
https://www.pbs.org/video/bbq-franklin-episode-4-pits/

This is a very good video to watch before building a smoker. This video is were I got a lot of info before building my 500 gallon off set. Works amazing.

 

[indaswamp]

I agree with dave...3" minimum exhaust stack.

 

[Marcsmith]

so no real need to get close to the EX stack volume of 147.4 so long as i'm not under

 

[indaswamp]

so no real need to get close to the EX stack volume of 147.4 so long as i'm not under

stack volume plays into draft pull and chamber gas turn over rate. Too much air flow and meat will dry out, smoke travel will be too fast... You can go a little larger, but if you mess up and go too small, you got to cut it out and put in a larger one.
Sometimes larger helps if you cram a lot of meat on the grates (which obstructs airflow) and more draft will help overcome this......

 

[daveomak]

Air flow can be totally controlled using the upper and lower air intakes on the FB.... As long as your smoke is air tight....

 

[Marcsmith]

thanks guys... now just gotta get the valve out and start the rinse.

 

[Marcsmith]

Rinse number 1 It was a breezy day so not much smell lingered did a rinse with fresh water first drained and then filled with one gallon of bleach, one gallon simple green and the rest water. And let it sit.

 

[Marcsmith]

I would go with 15" FB... Insert it past the weld seam.

Dave, the weld seam on the tank is in the middle and it runs around the circumference of the cylinder. the two hemispherical ends look like they were formed as part of the tank halve.

the hole where the tank valve was, is that as good of a location as any to set up the plenum/stack?

 

[daveomak]

Cool.... No weld seam to screw up the fitment....

 

[Marcsmith]

Cool.... No weld seam to screw up the fitment....

nope....only my ability to cut a a straight line

 

[Marcsmith]

Well second rinse ended up with a tea colored liquid coming out. Third rinse was clean with minimal mercaptan odor. And the inside looks pretty good as well. Hopefully will start with marking up the tank for door and fb cut this weekend...