Chimney pipe re fabrication

[NorthernLightsBbqCo]

Hello everyone. My name is Todd & I'm a backyard BBQ cook in Calgary, Alberta Canada. A welder friend & I have built a traditional offset smoker for myself & it has been plenty of fun to use so far. I am not getting even temperatures across the length of the cook grate. At times the temperature differential from close to the firebox to the chimney end can be 50F or more. I know some people like having a varience in temperature but I would like to get the grate temperatures more even across the whole grate. I believe some of the problem is that my pipe opening is towards the top of the cook chamber end piece & it is drawing the air from the bottom close to the firebox in a diagonal plain up to the chimney on the other end. I am considering re fabricating the pipe end of the cook chamber to include a collector at the outside end of the cook chamber for the chimney to sit on. Would that be considered a good idea? I am looking at adding a smaller second level cook grate inside the cook chamber as well. I would like some information on a few other items as well:
- Is the throat opening size that I currently have the correct size?
- Should I have a deflector plate on the inside of the cook chamber directly above the throat opening to deflect the hot air down as it enters the cook chamber?
- If I add a collector to the pipe end, what approximate size (height & width) should that be?
- Is it good to have that collector opening starting an inch or 2 below the height of the cook grate?
- What height & diameter should my chimney be?

I realize I am looking for a lot of information and I would greatly appreciate any information & advice someone wants to share with me.

Here are the dimensions of my smoker:
- Cook chamber is 24"x60" rolled pipe
- Firebox is 24"x24" rolled pipe
- Throat opening is 7 3/4"x11 1/2"
- Chimney is 6.5"x24" with an extension of 6.5"x22" that I can add or subject if needed
- I have a small adjustable air inlet vent in the firebox door but I usually adjust the firebox door opening for air flow. I do not have a damper on the chimney yet but I plan to add one once I am done with the chimney fabrication.

[Dirtytires]

First step is to run your numbers thru the calculator and compare with what you have.

With that said, your exhaust size is more important than a "collector." As long as your airflow is adjusted properly, adding one probably won't make much of a difference in temps. Precise airflow is pretty important to get a small fire and more even temps. Tho many feel they can regulate air with a firebox door, you will have much better results and fewer temp swings with a slide vent mounted low on your firebox. Besides the inability to fine-control air with a door, you loose a large percentage of the heat out the door which requires a bigger fire and more temp swings. Personally, I would change this habit first and learn how to make a small fire...you want a small pile of coals and feed it just enough to maintain the coal bed. Open the door only once every 45 minutes and feed one to two small splits about 3 inches in in dia....smaller the better so you gain coals and not flame.

Speaking of temps, where are you measuring them? It is pretty common for the first 10-12 inches of rack space (next to the firebox) on a standard offset to be unusable. Not much you can do except add a deflector plate but still dont expect to get full rack space back as the heat still needs to come in. A good way to find your usable space is to take a temp measurement at the exhaust end and then move toward the firebox till you get outside your comfortable temp swing. My guess is your 50degree fluctuation was from end to end and really is pretty reasonable for an offset. Another thought is to drop a water pan on the grate next to the firebox. The water sometimes help smooth out the high temps a bit.

[NorthernLightsBbqCo]

Thank you very much for taking the time to share your knowledge with me Dirtytires. I appreciate the information. I will look at possibly changing the air damper in the firebox door. I have been using a water pan on the grate by the firebox lately & will continue with that. I'll run the numbers through the calculator again to be sure I have what I need. Have a great day & weekend ahead!

[hogaboomer]

50 degrees is pretty good, IMO.

[NorthernLightsBbqCo]

Thank you hogaboomer.