Direct vs Reverse Flow Offset

[Bwick84]

I am building a trailer smoker out of a 500 gallon propane tank that measures around 10 ft long and 3 ft in diameter. I have never used a reverse flow offset, only my direct flow where the firebox and chimney are on opposite sides. I have always used Aaron Franklins method of an open firebox door to maximize airflow. Is there much difference in taste by using a RF?

Also, something to keep in mind (and another question in itself). I am wanting this to be a budget build and I already have a 120 gallon propane tank I could use for a firebox. It measures 6.5 ft long by 2 ft in diameter. I wouldn't want to use the whole length of it since it would make it way too long. However, according to the calculators this would be way too small of a firebox. Would it be ok for it to be that small if I insulated it? I've seen many pits that there is no way the firebox is 1/3 the size of the cooking chamber. Take Aaron Franklins for example. He uses a relatively small firebox for his 1,000 gallon smokers.

One other thing to keep in mind I would like to use it in the winter and I live in Idaho where it can get chilly.

 

[AlwaysSmokey]

His firebox size (Franklin) is a 250 gallon cut in half. With a 24" pipe inside to make it semi-insulated.

I vote never go with undersized fireboxes.

Turn that 120 gallon into a grill, or a warmer on top of your FB.

A million ways,.. that's my .02. Good luck on the build. Keep us posted on the progress.

EDIT: You'll have to wait on a RF guy for the flavor question. I'm sure a Shirley or Lang owner will be along any min.

Regards,

Kevin

 

[Bwick84]

His firebox size (Franklin) is a 250 gallon cut in half. With a 24" pipe inside to make it semi-insulated.

I vote never go with undersized fireboxes.

Turn that 120 gallon into a grill, or a warmer on top of your FB.

A million ways,.. that's my .02. Good luck on the build. Keep us posted on the progress.

EDIT: You'll have to wait on a RF guy for the flavor question. I'm sure a Shirley or Lang owner will be along any min.

Regards,

Kevin

Yeah, I would want to insulate it as well if I used the smaller tank, although I would also add some mineral wool. Looking at the numbers (only looking at the outer tank) he is using a firebox that is 12.5% the size of his cooking chamber. If I were to cut mine in half it would be 12% of my cooking chamber.

 

[gtr]

I don't know about firebox size, and have never cooked on RF. I will say that I love my Klose and the fact that there are differing temps across the grate. A lot of times I'm cooking different things that are better with different temps, i.e. poultry closer to the firebox, ribs further away, scooting butts or whatever closer to the firebox to set bark, etc.

 

[AlwaysSmokey]

I was talking with a friend,.. just this last weekend, about firebox size for a 500 gallon. I actually suggested the 250 half, but he seemed to think something bigger was called for. A 34x34x34 box was his final thought.

As far as Franklin,.. or anyone for that matter,.. what you decide to put on your pit is your call. I think he just stuck to what he knew, using the 250 half, from building his 500 gallon. That 120 just seems little to me. But hey,.. that's the magic of this hobby/job/pastime/life style/ .... There's millions of ways...

Regards,

Kevin

 

[AlwaysSmokey]

And,... I guess my undersized firebox vote is scrubbed since I didn't realize the 250 gallon half was that undersized for a 500 gallon.

LOL


Regards,

Kevin

 

[Bwick84]

I don't know about firebox size, and have never cooked on RF. I will say that I love my Klose and the fact that there are differing temps across the grate. A lot of times I'm cooking different things that are better with different temps, i.e. poultry closer to the firebox, ribs further away, scooting butts or whatever closer to the firebox to set bark, etc.

Yeah, it could definitely be useful at times. Do you have just one cooking grate on your Klose or multiple stacked?

 

[Bwick84]

I was talking with a friend,.. just this last weekend, about firebox size for a 500 gallon. I actually suggested the 250 half, but he seemed to think something bigger was called for. A 34x34x34 box was his final thought.

As far as Franklin,.. or anyone for that matter,.. what you decide to put on your pit is your call. I think he just stuck to what he knew, using the 250 half, from building his 500 gallon. That 120 just seems little to me. But hey,.. that's the magic of this hobby/job/pastime/life style/ .... There's millions of ways...

Regards,

Kevin

I know in the end it's my call but was just curious what everyone's thoughts were.

 

[COS]

Maybe franklins firebox is to small. I think he is compensating for it with a large exhaust stack to get draft and pull from the firebox.

 

[ShencoSmoke]

I just finished building my 500 gal direct flow offset. I used a square firebox, 34" wide, 34" deep, by 30" tall with 1-1/2" of insulation around the sides and top. It cooks evenly across the entire grate. I have a build thread if you want to check it out. I'm very happy with it, if I have a good fire burning it sticks between 275-300 with very little effort

 

[gtr]

Yeah, it could definitely be useful at times. Do you have just one cooking grate on your Klose or multiple stacked?

I have 2 grate levels, both grates slide out. The temps will differ more at the beginning of the cook, as much as 75 degrees, and a few hours in it's more like 25 or so degrees different. I also have a warmer, which can be 50 or 25 degrees cooler than the cool side depending on whether or not I have the pop baffle in.

 

[Bwick84]

Maybe franklins firebox is to small. I think he is compensating for it with a large exhaust stack to get draft and pull from the firebox.

That's kind of what I was wondering about if it works for him because he leaves his firebox door open and has a big exhaust. I was thinking of using a 10" diameter stack to help with airflow.

 

[Bwick84]

I just finished building my 500 gal direct flow offset. I used a square firebox, 34" wide, 34" deep, by 30" tall with 1-1/2" of insulation around the sides and top. It cooks evenly across the entire grate. I have a build thread if you want to check it out. I'm very happy with it, if I have a good fire burning it sticks between 275-300 with very little effort

I did read through your build thread, outstanding work! You said it cooks evenly across the grate, is there any temperature variation between sides? If I remember correctly you insulated your firebox, right?

If I cut my 120 gal tank in half it would essentially be 33" in length and 24" in diameter. I could obviously go a little longer but not sure if that would help anything.

 

[Bwick84]

I have 2 grate levels, both grates slide out. The temps will differ more at the beginning of the cook, as much as 75 degrees, and a few hours in it's more like 25 or so degrees different. I also have a warmer, which can be 50 or 25 degrees cooler than the cool side depending on whether or not I have the pop baffle in.

What size smoker do you have?

 

[ShencoSmoke]

I did read through your build thread, outstanding work! You said it cooks evenly across the grate, is there any temperature variation between sides? If I remember correctly you insulated your firebox, right?

If I cut my 120 gal tank in half it would essentially be 33" in length and 24" in diameter. I could obviously go a little longer but not sure if that would help anything.

im not big on probes and wires all of the place but when its loaded down the meat gets done at the same time (assuming similar sized meats). you can tell by the color of these butts that it is even across the grate. it drafts incredible. the only downside to my smoker is it is hard to reach the back. that could be handled with a slide out, but when i reach to the back the air draft hits you in the ear. and yes, the FB is insulated on sides and top.

 

[1MoreFord]

The Feldon BBQ Calculator Pit shows the firebox should be about 1/3 the volume of the cook chamber.

 

[Bwick84]

im not big on probes and wires all of the place but when its loaded down the meat gets done at the same time (assuming similar sized meats). you can tell by the color of these butts that it is even across the grate. it drafts incredible. the only downside to my smoker is it is hard to reach the back. that could be handled with a slide out, but when i reach to the back the air draft hits you in the ear. and yes, the FB is insulated on sides and top.

Looks great. Now that you've used it a bit, would you change anything you did?