First Off-Set Smoker Drawings - Advice Welcomed

[Cheese Burger]

Good morning Everyone

I've drawn up my plans for my first off-set smoker build based on Dave's calculation and Mike243's advice on insulating the firebox. So I've decided to insulate the top, bottom and both sides. Except the door and the back wall.

Ideal dimensions for a 24inch diameter x 51inch length pipe:
Volume in cubic inches –
24 x 24 x 0.7854 x 51 = 23,072 cubic inch

FB/CC opening –
23,072 x 0.004 = 92.2 square inch

Minimum volume of firebox –
23,072 x 0.33 = 7,614 cubic inch

I've decided to go with 20in (wide) x 24in (high) x 28in (long) = 13,440 cubic inch. I under it's almost twice as large as the recommended volume for the firebox. My reason behind it is that I wanted the width to be the size of the cooking chamber (minus 5inch for the insulation). The longer length will give me room to move the fire towards the cooking chamber or away from it, as necessary, to control the temp. Any thoughts on this?

Area of Firebox air inlet –
23,072 x 0.001 = 23 square inch

I've gone with 3 inlets for under the fire grate at 2x3inch and 2 inlets at the top at 2x2inch, which gives me 26 square inch. It's slightly over the recommended.

Volume of exhaust stack –
23,072 x 0.022 = 508 cubic inch

Length & diameter of exhaust stack –
4.5inch diameter stack and 32in above CC, which equates to 41inch from top of collector.

What are your thoughts on a internal butterfly damper in the stack as opposed to a stack cap damper?

Any constructive criticism or advice would be much appreciated. Thank you in advance.

 

[phoenixsmoke]

I've decided to go with 20in (wide) x 24in (high) x 28in (long) = 13,440 cubic inch. I under it's almost twice as large as the recommended volume for the firebox. My reason behind it is that I wanted the width to be the size of the cooking chamber (minus 5inch for the insulation). The longer length will give me room to move the fire towards the cooking chamber or away from it, as necessary, to control the temp. Any thoughts on this?

Area of Firebox air inlet –
23,072 x 0.001 = 23 square inch

I've gone with 3 inlets for under the fire grate at 2x3inch and 2 inlets at the top at 2x2inch, which gives me 26 square inch. It's slightly over the recommended.

Volume of exhaust stack –
23,072 x 0.022 = 508 cubic inch

Length & diameter of exhaust stack –
4.5inch diameter stack and 32in above CC, which equates to 41inch from top of collector.

What are your thoughts on a internal butterfly damper in the stack as opposed to a stack cap damper?

Any constructive criticism or advice would be much appreciated. Thank you in advance.

I am also working on a smoker build and have done fairly extensive research on it. I plan to build one with a CC that's 20" Diam X 48" long and FB 20" D X 24" long. Feldon's calculator puts this at 150% of recommended volume. Feldon's calculator recommends FB be 1/3 volume of CC. I agree with your reasoning on the size of the firebox. Here is a link to a video from Jimmy Daniel of Primitive Pits (he also makes the Workhorse pits): . He discusses Feldon's calculator and shows some graphics, pretty interesting.

As far as insulating, you should do some research on this. I have read that insulating a firebox can make it too efficient. My thoughts on this are that insulating a firebox introduces more complexity, cost and weight to the smoker I plan to build which is why I don't plan on insulating mine. I've decided to try and simplify my smoker build as much as possible because I tend to overthink things and it leads to analysis paralysis and I would never get off the ground on actually building it. I will likely be doing experiments on the one I build including trying out some firebricks or wrapping the firebox with a fire resistant insulating blanket to see if it makes a difference. If there is a material difference then it it would give me an excuse to do another build.

I'm still thinking about what to do with firebox door inlets. I will likely include some on the lower part of the door (vertical slits about 1" wide X 3" tall and put in 5-7 of these). I've also thought about not doing any door inlets and just use the door to control the inflow. Feldon's calculator says that if I have a total of 21 sq in of intake that would be sufficient (7, 1"x3" openings). I will probably not put a slider on them but rather leave them wide open as I figure it would be a simple addition to weld on a slider later.

EDIT: I just read through this thread: https://www.smokingmeatforums.com/threads/whats-wrong-with-this-smoker.307465/post-2214630 where daveomak explains that adding inlets at the top adds airflow to the CC without adding air to the fire. He recommends adjustable top and bottom inlets to control inflow depending on what you want to control. Based on this you're probably fine and may want to consider adding adjustable inlets to dial it in.

I don't plan on putting a stack damper on mine at this time. Again, just trying to keep things simple. I'm more interested in stack height and I am considering making mine out of 4" or 5" (still researching the diameter of the stack) 36" to start with and then fabricating 6" stack extensions out of thin sheet metal to experiment what would be ideal. I hope that I can achieve a relatively ideal height and not have to worry about a damper.

Good luck on your build and keep us updated with your progress and what you decide to do.