250 gallon first build-HELP PLEASE!

[PoPs54]

OK folks, about to start my first smoker build. I have the propane tank and a very skilled fabricator friend that is helping me (his first smoker build also). I am building a reverse draft smoker. My tank is a 250 gallon propane tank that is made out of 1/4" material. I want to use the tank for both my fire box and cooking area. I think I have seen information somewhere on calculating the drop for the offset on the fire box. If someone could help me with that it would be very much appreciated. As far as the rest of the calculations, I have come up with the following, the tank is roughly 30" dia. by 90" long. If I make the cook area 30" X 66", and the fire box 30" X 24", I think that should work for the correct sizing. As for the smoke stack, I am thinking 6" X 30". The outside intake for the fire box should be 16" X 3" or 9" dia. I am not sure I understand the dimensions for the intake. Is it considering the fact that you will be opening the mechanism and allowing only as much as 50% of that area, or do you adjust overall size so you have 100% of that area open? Lots of dimensions here and I am not sure they are correct. There are probably lots more I need, but this will be a good start. I sure will appreciate any help and advice you can give me.

[Frank_Cox]

I'm not on my compy yet... I will be on later tonight and I will help ya out.

Sent from my iPhone using Forum Runner

[Smoker Tom]

Hi Pops,

I am not 100% sure on this since I have not personally built a propane tank rig, but I believe you can come pretty close if you build the firebox 1/3 the size of the cook chamber.

I'm not even gonna try and run your numbers since I have worked way to many hours in the last two days to even see straight. If I manage to not get called in over night I will look at them in the AM.

[Smoker Tom]

By the numbers, you are pretty close for your firebox size compared to the cook chamber.

I was going to try and give you an idea for how much offset you needed for the firebox but it seems that I have a bad link to my circle calc that I use.

What I did on my RF round tanks, was find the area of the football shaped piece between the two tanks and make the dim match the area needed between the fire and the food.

There is no problems if you make the fire to food opening a little bit bigger then actually needed and in some cases it can even help out if you have it set up as a damper.
Personally I don't care to get the face full of smoke every time I have to get in the rig. So I like to have a damper that I can close off if I want to. One or two things I dont care, but when I have to move a ton of stuff I hate the smoke in the face.

Its also to have the RF plate gap a little large and run an adjustable damper there as well.

For your question about the air intake.

If it said 9", then you would want one 9" hole cut clear with a cover that could slide over that opening.
For a 9" opening, I would use two 10" butterfly dampers.

You can use any number or shape of openings so long as you give it the recommended area for air intake.
Here is a less then perfect vent on one of my smokers. This vent is about 7 or 8 inchs and the rig is 42" for the food and 22 I think it was for the fire.

[PoPs54]

Frank, thanks for the reply and I look forward to your input.

Smoker Tom, thanks for the good information. I also like the idea of a damper between fire and food but never thought about the added benefit of cutting the flow of smoke off while having the door open - great idea. I am hoping for some accurate figures on the firebox drop, calculations on that sort of thing are not my strong point (must have slept through all those classes). I am still a little confused about the air inlet to the firebox. If the calculator says I need 16"X3" or 9" dia. opening, that means that if wide open, there needs to be an area 16"X3" or 9"dia. for flow which would mean if I had dampers on the openings that would only allow 50% of the area to be open I would need to cut the opening double the size as in 16"X6" or as you said for the butterfly type 2 at 9" dia.or 10"dia. I hope I am making sense with my statements, I think I may be confusing myself. Look forward to hearing from you.

[Smoker Tom]

Your right on the money in your thoughts about the air intakes.

What ever the numbers are, thats what you need when they are wide open.

I will get with Frank and figure out what has happened with the calc we were using.
If we have to we can work the formula the old way.

I'm am gonna make a wild guess here and say that I bet the firebox will overlap the food box by about 14 to 16 inchs. DONT use that number yet, its just a guess.

The best way that I can think of for the damper between the food and the fire would be to place a rod from front to back across the long point of the football shaped piece.

The back side can simply be a nut just larger then the rod, so the rod sits in it like a socket.
The front side, the rod is just thru a hole in the front side of the intersecting point of the two chambers.
Then have a locking collar with set screws to the rod on the inside of the tank.

Just something to think about.

[Smoker Tom]

Found it !!!!!!!!! HA...

It seems that the calc belongs to a certian person and they had it hosted on a site and someone stole it. They are working on getting it back to its original location..

Here is a screen shot of your numbers.

I used a radius of 15
and segment height is 5"

Now what this means is this area is only half the football. Double it and make the opening 10" from the inside top of the firebox to the inside bottom of the food chamber.
This is if you are using flat ends. If you cut the firebox into the helical end of the propane tank the 10" can be less due to radiant heat. Franks knows well the details of this.
I assume you will have flat ends since you are cutting both from one chunk of pipe.

[Frank_Cox]

hi pops!
looks like smoker tom is gettin ya squared away
the best way to to attach fire box to cookchamber in my opinion is always with 2 flat plates if you can live with the looks of that type of config. no problem with the other way really just makes it easier.

[Smoker Tom]

Here is a couple shots of the way I did my last build, its not a propane tank and its much smaller then what you are working on but the idea is still the same.

[PoPs54]

I have got questions but will have to wait till tomorrow. It has been a full schedule tonight.