New member here! Looking for firebox advice w/pictures

[JMF86]

So I have been using a vertical propane smoker for convenience but dearly miss the flavor that my old offset produced. Having recently purchased a new welding machine, the only logical option is to build a 250gal reverse flow and a trailer for it to be mounted on.

I knew my FIL had an extra 250 gal tank that I could get for cheap. He also had several different lengths of 5" square tubing, some angle iron and other pieces of random steel that he offered to go towards my project. All I needed to find was a reverse flow plate and some plate for my firebox. I called a local scrap yard and they said we have a big stack of thick plate you can come look at.

The plate they had was plasma cut 5/8" and were all exactly the same size 2' 10.75" x 2' 6.75". Nice perfectly square edges!!! Jackpot!!! I went home beveled the edges, welded them up into a monster of a firebox, made a door, door handles, latches.

Then I found feldons calculator.

My cooking chamber is 250gal or somewhere around 58,000 cubic inches which means my firebox should be around 19,200 cubic inches. My firebox as built is closer to 28,000 cubic inches.

I can see only 2 good options here.
1. I haven't welded the back plate on yet and could cut the length of the firebox from 34" long to whatever number you more experienced folks would reccomend
2. Look for a 325gal tank and have a bigger smoker than I will ever need.

What should I do here?

Thanks, John

 

[daveomak]

Before you get too far with Feldon's, read our tutorial.....

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

 

[JMF86]

Before you get too far with Feldon's, read our tutorial.....

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

I have read that tutorial several times also but I'm not really sure I'm using it right. When calculating the area needed under the reverse flow baffle does it mean the total volume in inches under the length of the whole baffle?

 

[daveomak]

I have read that tutorial several times also but I'm not really sure I'm using it right. When calculating the area needed under the reverse flow baffle does it mean the total volume in inches under the length of the whole baffle?

Well, you have to understand I took certain liberties when putting this together....
The numbers calculated can be either area or volume....
FB/CC openings are area... Under the FB is also area, kind of screwy but, if I noted it in volume, you would have to go through another calculation to figure out the height above the bottom of the CC...
I guess the best way to think of it is a 1" wide slice of the cross section...
Am I screwing this up for you ?????

 

[JMF86]

Well, you have to understand I took certain liberties when putting this together....
The numbers calculated can be either area or volume....
FB/CC openings are area... Under the FB is also area, kind of screwy but, if I noted it in volume, you would have to go through another calculation to figure out the height above the bottom of the CC...
I guess the best way to think of it is a 1" wide slice of the cross section...
Am I screwing this up for you ?????

My tank is 250 gal. My firebox measurement is 30 inches wide, 29 inches tall and 34 inches long but can have the length cut down since I haven't welded the back plate on yet. I also have a piece of 5.5 inch square tubing that I had planned on using for the chimney and was going to make it around 42" tall. I have a full 5x10 sheet of 3/16 to make my baffled out of and maybe a collection header if that would be better? If I came up around 10 inches off the bottom of the tank and welded my baffle would that be enough? I could leave the whole end open from the weld ring out to allow smoke to turn around the end of the baffle.

 

[daveomak]

Feldon uses the size of the FB to calculate all the other stuff, which makes no sense....
I use the size of the Cook Chamber to make the calculations...
So, if you wouldn't mind, what is the length and diameter of your cook chamber and I will run some numbers...
Dave

 

[JMF86]

Feldon uses the size of the FB to calculate all the other stuff, which makes no sense....
I use the size of the Cook Chamber to make the calculations...
So, if you wouldn't mind, what is the length and diameter of your cook chamber and I will run some numbers...
Dave

The tank is 7' 6 long and 2' 7 wide. I found a good source for 2.5" thick firebrick that I could line the inside with if needed. Yesterday I worked on getting the doors cut and the handles placed. Now one of the doors isn't wanting close flush. Thank you for your help!

 

[JMF86]

I got the door issue fixed. You can see the size of the firebox here compared to my cooking chamber.

 

[daveomak]

You will have to cut the hinges loose, reposition and weld again... Welds shrink...

AND they are welded in the wrong place....

They need to be welded, the center line of the hinge pin must be OUTSIDE the door flange...

Weld with some extra material so you can "adjust" the door position... The "BLUE"..

 

[daveomak]

90 x 30 =

63,600 cu. in./ 231 = 275 gal... The label may say 250 but... they allow for gas expansion...

63,600 x 0.004 = 254 area sq. in. or cubic inches depending on where it goes...

 

[JMF86]

You will have to cut the hinges loose, reposition and weld again... Welds shrink...

AND they are welded in the wrong place....

They need to be welded, the center line of the hinge pin must be OUTSIDE the door flange...

View attachment 469540

Weld with some extra material so you can "adjust" the door position... The "BLUE"..

View attachment 469541

I got the idea to mount the hinges that way from watching a YouTube video from IronmanJack out of Georgia. He mounts the top plate and his hinges so that when it rains the top acts like a diverter and channels the water down and around the door. Here is a screenshot off of ones of his videos showing his design.

The door fit was good until I cut it completely in the last corner. I guess the tank had some tension that turned loose. I was able to grind some off of the top of the door where the door meets the tank at the cut line and achieve a good fit.

I thought the 250 gallon tank was 250 gallon filled to 80% capacity. What would be the problem with cutting my tank up to the weld line about 10" from the bottom and cutting the the whole opening out of the back of the firebox where it protrudes into the cooking chamber? I know that hole can be to small and prevent proper airflow. Can it also be to large?

 

[daveomak]

As far as the size of the opening between the FB and CC, the tutorial will guide you through that calculation..
https://www.smokingmeatforums.com/t...eady-to-use-rev5-6-19-15.172425/#post_1264161








Reverse flow plate with drain hole....

Weld seam inside a propane tank.... You can cut horizontally into the tank and slide the Fire Box in as far as you like...

 

[JMF86]

I made some progress today. Stack is 44" x 5" 3/16" wall square tubing and cut at a 45° angle and inserted about 6" total into the coming chamber.

The cc/fb opening is 21 inches wide and 5.5 inches at the widest part in the center. Does that sound about right?

Reverse flow baffle is welded at the same height as the top of the firebox and terminates at the ring at the other end. The whole end is open for airflow. Will be adding pipe drain and valve tomorrow and start working on grates and a drop down table.

Any obvious mistakes that I need to fix? Thanks, John

 

[daveomak]

If your CC is 31" diameter, from the other numbers I see here, the FB/CC opening should be about 250 sq. inches....

If you cut out the FB to sort of match the green, the height of the cut out ED, should be 12" high..

 

[JMF86]

12" segment height would be nearly half of the cooking chamber wouldn't it?

 

[daveomak]

31" diameter and 12" to the RF plate...

 

[daveomak]

Use this tutorial for all your measurements...

Standard Reverse Flow Smoker Calculator... by DaveOmak and others... Ready to use.. rev5.. 6/19/15.

Here's to "Alien BBQ" and the folks that first put the calculator together and "1728 Software Systems" for this great "Circle Calculator" and all the folks at "SmokingMeatForums", with a special shout out to Ribwizzard, that contributed their ideas and feedback while this thing was coming...

www.smokingmeatforums.com

 

[JMF86]

Today I cut in my lower air intake and installed my pipe for the grease drain. I was a little concerned about not having enough air flow so I made a small fire and it draws really well. I still need to make the upper air intake, cooking grates, add the fire bricks inside the firebox and get this thing mounted on a trailer. Pretty happy with what I have so far.

 

[JMF86]

I smoked my first 2 briskets this week. They turned out great! Used post oak, salt, pepper, and 2 low quality select grade briskets. It held temp very well and had very good draw. I need to seal around my cc doors with the gasket material I bought and get it mounted on a trailer now.