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Super Fantastic Fun Time 100lb RF Build

CapnJames

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Hello everyone! I have acquired an old 100# propane tank and am converting it over to a reverse flow smoker. Holla! I have ran the numbers and would like your input on my calcs.

Volume is coming in @ 6616 cubic inches. Based on numerous comments about longer cooking vessels, I bumped this up 10% for the remainder of the calcs.

Segment area requirement (includes the 10 point bump) is coming in at 29.1 sq in. I have it at 30.5 sq in.

Fire box requirement is at 2400 cu in. 15x15x15 gives me 2580 cu in. Is there a more ideal shape than a straight up cube?

Stack requirement is 176 cu in. A 3" (id 2.5") pipe 40" in length will give me 196.35.

As for the reverse flow plate. The distance between the end of the plate and the end of the smoker. Do you take the measurement for the gap from the start of the curve on the tank or the peak of the curve?

Thanks in advance folks!

James
 

daveomak

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Long and narrow RF smokers have a higher friction to area ratio and increased areas should be included... It may not flow air too well.....
Of course that depends on the tank diameter...
Did you use our tutorial ???


...
 

CapnJames

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daveomak daveomak The inside diameter of the tank is roughly 14.5" and the length is roughly 40". I followed the guidelines in the initial post and excel sheet on the next to last page. I added 10% to the volume to come up with the remaining values. I am not opposed to cutting the tank down, it is just the three of us at the house with the occaisonial holiday entertaining. I just need room for 2/3 butts or briskets. I would prefer not to cut it down, but if that will make it work better.. My welding skills are pretty novice by the way lol.

Is there a rough guideline for length X width ratio that is ideal to marry up with your numbers at the beginning of the tutorial?
 

civilsmoker

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If you search through the reverse flow builds threads there are many good examples of similar builds. Here are just a few worth reading for educational purposes.

https://www.smokingmeatforums.com/threads/patio-rf-100-lb-propane-tank.175266/

https://www.smokingmeatforums.com/threads/100-rf-propane-tank-smoker-build.249915/

https://www.smokingmeatforums.com/threads/20gal-build-finially-done.155432/

I didn't look over your numbers very closely but I would use at LEAST a 20% (25 to 30 would be better) increase of critical air flow numbers with the build...As in the builds above the fire box is bigger the opening is bigger and stack is way bigger.......
 

CapnJames

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Thanks for the suggestions civilsmoker civilsmoker . I have seen those build threads. Not much feedback after the builds were complete, it would be nice to see if they performed well or ended up as yard art.
 

civilsmoker

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Thanks for the suggestions civilsmoker civilsmoker . I have seen those build threads. Not much feedback after the builds were complete, it would be nice to see if they performed well or ended up as yard art.
As Dave said the 100# tank is long and has a small diameter. It doesn't matter what you do to it, it wont flow as well as a chamber that is say 1to2 ration vs 1to3 ratio (L to D) (I'm not saying it won't work just not as well). I think that is why those builds have a longer stack, ie to help with flow. If you look at the scrap yard or adds you maybe able to find an old 30 gal air tank. These have a much better ratio than the 100# tank. I was able to buy 3 air tanks for 65 bills and one of those was for my Copper Pot build. It's best to be patient and do it right the first time as it equals YEARS of happy cooking.

Just food for thought, if you are set on the 100# you could split it in 1/2 and make it more like a Shirley build (It does require a bit more fabrication ) and that would solve the ratio (again not that is a huge problem) and make it a double rack height smoker (it would be very cool to!). I have a future build planned that will be like this, just have too many honey do lists......
 
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CapnJames

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Joined Jan 7, 2021
As Dave said the 100# tank is long and has a small diameter. It doesn't matter what you do to it, it wont flow as well as a chamber that is say 1to2 ration vs 1to3 ratio (L to D) (I'm not saying it won't work just not as well). I think that is why those builds have a longer stack, ie to help with flow. If you look at the scrap yard or adds you maybe able to find an old 30 gal air tank. These have a much better ratio than the 100# tank. I was able to buy 3 air tanks for 65 bills and one of those was for my Copper Pot build. It's best to be patient and do it right the first time as it equals YEARS of happy cooking.

Just food for thought, if you are set on the 100# you could split it in 1/2 and make it more like a Shirley build (It does require a bit more fabrication ) and that would solve the ratio (again not that is a huge problem) and make it a double rack height smoker (it would be very cool to!). I have a future build planned that will be like this, just have too many honey do lists......
I hear you on the honey do list lol. Thanks for taking the time to point me in the right direction and reminding me to simmer down / slow my roll. I am itching to have the grinder throw sparks and stack some dimes lol.

The Copper Pot is a sweet a$$ build, looks nice! That reverse sear grate is bloody brilliant. I need to read the whole thread to see how it came along, looked at the first and last pages.

I have been keeping my eye out on FB marketplace and CL for propane tanks and compressor tanks. I have not came across any winner winner chicken dinners yet. The compressor tanks I have seen at the yard are rusted and beat to hell. It might be easier to just fab an octagon cylinder. Not as sexy and romantic as an upcycled tank though. There is a steel supply company about 1/2 an hour away, I will give them a shout.

Thanks again!
 

daveomak

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I have been keeping my eye out on FB marketplace and CL for propane tanks and compressor tanks.

Thanks again!
I have a 500 gallon tank for sale.... If you are in the neighbor hood....




Propane tank 001.JPG
 

daveomak

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I guess I'll be looking for you in a few weeks then...
 

CapnJames

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Gentleman down the road had a 60g. Bottom is a little pitted, not bad considering she was built in the 50's. 22" outside diameter and about 42" long. Gave me the whole "I have other people interested.. " 50$ later she is in my garage upside down with the valve off. Not sure if it was a great decision, it is a little bigger than I originally intended. I feel like it is borderline trailer size, not my back patio size lol. I can always make a fireplace / boiler for the garage out of it. Thoughts?

Edit: she is a beast of a tank. A tank of a tank.
 

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daveomak

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Thanks for the suggestions civilsmoker civilsmoker . I have seen those build threads. Not much feedback after the builds were complete, it would be nice to see if they performed well or ended up as yard art.
Folks that follow the tutorial our members put together, DO NOT end up as yard art... They end up with awesome smokers..



 
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CapnJames

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daveomak daveomak I have bought in on the concept. I was referencing the 100# builds that civilsmoker civilsmoker had shared with that comment. I apologize if any offense was taken, I was poking the 100# long concept. The 1x2 (diameter x length) ratio for the CC seems to be the constant that runs through the successful builds.

I jumped in both feet first with the 100# tank without doing the research first. There are a lot of those empty and available in my area. They fit in the back of the hatchback easy too hahaha.
 

daveomak

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No offense taken....


Dave
 

civilsmoker

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daveomak daveomak I have bought in on the concept. I was referencing the 100# builds that civilsmoker civilsmoker had shared with that comment. I apologize if any offense was taken, I was poking the 100# long concept. The 1x2 (diameter x length) ratio for the CC seems to be the constant that runs through the successful builds.

I jumped in both feet first with the 100# tank without doing the research first. There are a lot of those empty and available in my area. They fit in the back of the hatchback easy too hahaha.
What dave says is spot on he is the expert! By the way, your new tank is very sweet by the way! If you follow the guild that will make a top self smoker all around! PS I don't think its too big for a yard smoker!
 

CapnJames

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What dave says is spot on he is the expert! By the way, your new tank is very sweet by the way! If you follow the guild that will make a top self smoker all around! PS I don't think its too big for a yard smoker!
Thanks for feedback! I have been kicking around fabricating an octagon with plates, but I have no experience welding. I think I would give up and walk away from the project if I went that route lol. Time to scrounge up some 1/4" plates for the firebox and legs for the stand!
 

CapnJames

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daveomak daveomak Do you think a 60 gallon propane tank warrants the additional 20-30% when calculating everything? I picked up a 4' piece of 4" OD steel pipe from a job site the other day. Sure would be nice to use this as the exhaust stack.
 

daveomak

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Try it and see what happens..... If the smoker doesn't flow well, then you can replace it...
 

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