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Rod630

Newbie
Original poster
Oct 7, 2020
11
1
I am getting ready to build a trailer smoker, this is my first build so I want it to be correct. I have done some research and would like someone whos done a build to double check before I proceed with fabrication. Below is what I have came up with using the feldon calculator. This will be a reverse flow. If anyone has some good links to builds or has any good advise to give would be greatly appreciated!

-CC dimensions=33" dia.x 72" L.
-FB dimensions=26"H x 33"W x 24"L
-Chimney= 6" pipe x 36.43" Long
-Intake= 6" length x 1", (10-11 needed)
-FB/CC opening= 20.48" half moon
(164.74sq.in.)
-Would a round firebox box be more efficient than a square or rectangle one?
-How high should the baffle plate be above the firebox opening?
-What would be an acceptable height between the baffle plate and cook grate?

TIA- Rod-
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1

Big Bad Wolf

Newbie
Jul 31, 2022
15
6
I am getting ready to build a trailer smoker, this is my first build so I want it to be correct. I have done some research and would like someone whos done a build to double check before I proceed with fabrication. Below is what I have came up with using the feldon calculator. This will be a reverse flow. If anyone has some good links to builds or has any good advise to give would be greatly appreciated!

-CC dimensions=33" dia.x 72" L.
-FB dimensions=26"H x 33"W x 24"L
-Chimney= 6" pipe x 36.43" Long
-Intake= 6" length x 1", (10-11 needed)
-FB/CC opening= 20.48" half moon
(164.74sq.in.)
-Would a round firebox box be more efficient than a square or rectangle one?
-How high should the baffle plate be above the firebox opening?
-What would be an acceptable height between the baffle plate and cook grate?

TIA- Rod-
Your reverse flow cooker is nearly the same size as mine. Mine has a 36" dia. cook chamber x 60" lg. The total internal dims of both are nearly the same. To answer a few of your ?? I would make a rectangle firebox at .333 the size of the cubic inches of your cook chamber. The size you have listed is close to what you need. The baffle plate should be at the top of your firebox to cook chamber opening....it's just a continuation of the top of your firebox. The top of my lower grate is 4" above the 1/4" baffle plate and seems to work great. You will need about 62 square inches of air inlet openings on your firebox. The majority of air inlet openings need to be below your fire and the remainder in line with your opening from the firebox to cook chamber. The ratio is about 80% below fire and 20% in line with your firebox to cc opening. The length of your exhaust stack needs to be calculated above the top of the cook chamber. I have pictures posted here of mine. Maybe will give you a few ideas. Big Bad Wolf.
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
Your reverse flow cooker is nearly the same size as mine. Mine has a 36" dia. cook chamber x 60" lg. The total internal dims of both are nearly the same. To answer a few of your ?? I would make a rectangle firebox at .333 the size of the cubic inches of your cook chamber. The size you have listed is close to what you need. The baffle plate should be at the top of your firebox to cook chamber opening....it's just a continuation of the top of your firebox. The top of my lower grate is 4" above the 1/4" baffle plate and seems to work great. You will need about 62 square inches of air inlet openings on your firebox. The majority of air inlet openings need to be below your fire and the remainder in line with your opening from the firebox to cook chamber. The ratio is about 80% below fire and 20% in line with your firebox to cc opening. The length of your exhaust stack needs to be calculated above the top of the cook chamber. I have pictures posted here of mine. Maybe will give you a few ideas. Big Bad Wolf.
Your reverse flow cooker is nearly the same size as mine. Mine has a 36" dia. cook chamber x 60" lg. The total internal dims of both are nearly the same. To answer a few of your ?? I would make a rectangle firebox at .333 the size of the cubic inches of your cook chamber. The size you have listed is close to what you need. The baffle plate should be at the top of your firebox to cook chamber opening....it's just a continuation of the top of your firebox. The top of my lower grate is 4" above the 1/4" baffle plate and seems to work great. You will need about 62 square inches of air inlet openings on your firebox. The majority of air inlet openings need to be below your fire and the remainder in line with your opening from the firebox to cook chamber. The ratio is about 80% below fire and 20% in line with your firebox to cc opening. The length of your exhaust stack needs to be calculated above the top of the cook chamber. I have pictures posted here of mine. Maybe will give you a few ideas. Big Bad Wolf.
To this point, the only question I had was the stack height and where that measurement was pulled from and you confirmed what I thought as I had misunderstood that to begin with. Luckily I'm not to that point quite yet. Thank you for your reply! Pictured is what I got so far and all the info you provided is spot on with what I have currently. Trying to find time after work to work on it has been the biggest challenge so far!
 

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Big Bad Wolf

Newbie
Jul 31, 2022
15
6
To this point, the only question I had was the stack height and where that measurement was pulled from and you confirmed what I thought as I had misunderstood that to begin with. Luckily I'm not to that point quite yet. Thank you for your reply! Pictured is what I got so far and all the info you provided is spot on with what I have currently. Trying to find time after work to work on it has been the biggest challenge so far!
Looks like it is coming together nicely. I used a 7" dia. stack and I think it is 35" above the cook chamber. I built a plenum and mounted mine on the end above the firebox. Have two pullout grates in mine and can easily cook 24 - 28 Boston Butts with no problem. Just make sure the openings for your air flow are adequate between the firebox/cc and at the end of the reverse flow plate. they should be the same size in square inches. Mine holds even temps end to end within about 5 degrees with the door dial thermometers. I also use the Thermoworks Smoke readout for meat temp and cc temp.
 

Big Bad Wolf

Newbie
Jul 31, 2022
15
6
I am getting ready to build a trailer smoker, this is my first build so I want it to be correct. I have done some research and would like someone whos done a build to double check before I proceed with fabrication. Below is what I have came up with using the feldon calculator. This will be a reverse flow. If anyone has some good links to builds or has any good advise to give would be greatly appreciated!

-CC dimensions=33" dia.x 72" L.
-FB dimensions=26"H x 33"W x 24"L
-Chimney= 6" pipe x 36.43" Long
-Intake= 6" length x 1", (10-11 needed)
-FB/CC opening= 20.48" half moon
(164.74sq.in.)
-Would a round firebox box be more efficient than a square or rectangle one?
-How high should the baffle plate be above the firebox opening?
-What would be an acceptable height between the baffle plate and cook grate?

TIA- Rod-
I did some quick calculations on your unit. You have 61,581 cu. in. in your cook chamber. The recommendations on a reverse flow are cooking chamber cu. in. x .022 for the exhaust stack cu. in. All exhaust stack lengths are figured above the top of the cook chamber. You could use a 6" inside dia. pipe but should be 48" above the top of the cook chamber, or a 7" inside dia. pipe x 36" above the top of the cook chamber. Either will work. Since you already have 6" pipe I would use it but make it 48" above the top of the cook chamber.
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
I did some quick calculations on your unit. You have 61,581 cu. in. in your cook chamber. The recommendations on a reverse flow are cooking chamber cu. in. x .022 for the exhaust stack cu. in. All exhaust stack lengths are figured above the top of the cook chamber. You could use a 6" inside dia. pipe but should be 48" above the top of the cook chamber, or a 7" inside dia. pipe x 36" above the top of the cook chamber. Either will work. Since you already have 6" pipe I would use it but make it 48" above the top of the cook chamber.
Ha, I just double checked my math and I was wrong when I calculated it. You are correct! The exhaust should be at the grate level correct? If that's the case I come up with 48"+16 1/2"= 64 1/2" total pipe length. I am also making my baffle plate in 4 separate pieces so they are removable for cleaning. Everything should be a tight fit so I don't see any issues with that. Hoping to be complete with the smoker this week, then it's on to the trailer.
 

Big Bad Wolf

Newbie
Jul 31, 2022
15
6
Ha, I just double checked my math and I was wrong when I calculated it. You are correct! The exhaust should be at the grate level correct? If that's the case I come up with 48"+16 1/2"= 64 1/2" total pipe length. I am also making my baffle plate in 4 separate pieces so they are removable for cleaning. Everything should be a tight fit so I don't see any issues with that. Hoping to be complete with the smoker this week, then it's on to the trailer.
As for the location of the exhaust. Different people put them at different locations. If mounted on top you can extend it down into your cooker as far as you wish. Some people put the end of the pipe just a few inches above the grate and some people prefer the end be at the top of the cook chamber. I mounted mine on a plenum on the end of mine over the firebox and also made it removable for transport on the highway when cooking at places away from home. Had to make it that way also to get it into my building. I have my baffle plate, 1/4" thk steel made in one piece and welded in solid to my cook chamber sides. My grates slide out so no problem in cleaning the baffle plate.
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
As for the location of the exhaust. Different people put them at different locations. If mounted on top you can extend it down into your cooker as far as you wish. Some people put the end of the pipe just a few inches above the grate and some people prefer the end be at the top of the cook chamber. I mounted mine on a plenum on the end of mine over the firebox and also made it removable for transport on the highway when cooking at places away from home. Had to make it that way also to get it into my building. I have my baffle plate, 1/4" thk steel made in one piece and welded in solid to my cook chamber sides. My grates slide out so no problem in cleaning the baffle plate.
So I am thinking about going with a plenum design for the exhaust same as how you described your at the end above the fire box. Any specifics involving the design of the plenum or anything you learned building yours?
 

Big Bad Wolf

Newbie
Jul 31, 2022
15
6
So I am thinking about going with a plenum design for the exhaust same as how you described your at the end above the fire box. Any specifics involving the design of the plenum or anything you learned building yours?
Look at the pictures I have posted of mine. It shows somewhat how I did mine. I made mine 10" square I think and did about half of my bottom at a 45 degree angle. Make the inside large enough not to restrict your air flow.
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
Look at the pictures I have posted of mine. It shows somewhat how I did mine. I made mine 10" square I think and did about half of my bottom at a 45 degree angle. Make the inside large enough not to restrict your air flow.
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
So I made the plenum, 8"x24". Exhaust is 48" from the top of the cook chamber. Just seems long to me, but based on the math for 6" pipe it's correct.
 

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Rod630

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Oct 7, 2020
11
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Well, here it is. Going to get blasted on monday and paint next week. Only trouble I am having is getting it up to temp. I think I am using to green of wood and not a big enough fire. Any input on how big a fire your stoking yours to?
 

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JckDanls 07

Smoking Guru
OTBS Member
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Sep 10, 2011
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Tampa area, Florida.
That's a sweet looking rig right there Bub... great job

For my initial start up I stack up 5-6 splits on a half of chimney of lit charcoal and feed it all the air I can... After it gets well ignited I will close the door and run with vents wide open... This will pre-heat up to 350 or more... Let the fire burn down to coals... When it's ready for a single split I will spray the inside of the cook chamber with my garden hose... This does two things... 1. it will cool the steel back down to running temps... 2. Close the lid real quick after spraying and let it steam clean... BE VERY CAREFUL while spraying as the steam gushing out will be VERY HOT ... This will clean all the grates and only need a light brushing...
Close my vents down to where it likes to run at 240ish... Throw a fresh split on the hot coals and I'm ready to cook... Takes about an hour to pre-heat/clean ...
 

Rod630

Newbie
Original poster
Thread starter
Oct 7, 2020
11
1
That's a sweet looking rig right there Bub... great job

For my initial start up I stack up 5-6 splits on a half of chimney of lit charcoal and feed it all the air I can... After it gets well ignited I will close the door and run with vents wide open... This will pre-heat up to 350 or more... Let the fire burn down to coals... When it's ready for a single split I will spray the inside of the cook chamber with my garden hose... This does two things... 1. it will cool the steel back down to running temps... 2. Close the lid real quick after spraying and let it steam clean... BE VERY CAREFUL while spraying as the steam gushing out will be VERY HOT ... This will clean all the grates and only need a light brushing...
Close my vents down to where it likes to run at 240ish... Throw a fresh split on the hot coals and I'm ready to cook... Takes about an hour to pre-heat/clean ...
I ran a full chimney of charcoal with like 3-4 splits and added more to get it really roaring, but it just died off. How big of split are you using? I think what I got is still to green, over 25% moisture. You can hear the water dripping out of the wood when it's burning, pretty steadily.
 

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