Horizontal offset with vertical chamber

[brisket envy]

Good morning, fellow pitsters!
I have another question about the project I am working on:

When deciding upon the chimney size for a horizontal offset with vertical chamber, should I use the numbers right out of the pit calculator, or does the vertical chamber have somewhat of a chimney effect, allowing for possibly a shorter smokestack?

Thanks!

[Bkndsdl]

good morning to you too sir!

I asked the very same question not long ago. The chimney needs to be the length specified; the chamber does not subtract from that length. If the calc says 13", then it's 13" stack, no matter how far it is inside the chamber.

[brisket envy]

Thanks.
Are two 13" long 5" diameter chimneys the equivalent of one 26" x 5", since the total chimney volume would be the same?

[Richtee]

I would say no..as draw is related to length. The relation? I do not know. But you can always damp the exhaust if need be. Personally..I don't think you can have too much exhaust. Only too much intake.

[bgraham]

I agree with Richtee on exhaust stack length. Once the smoker is at operating temp the height of your stack affects the velocity of exiting gasses. On my current setup Feldons calculator recommended 48" @ 4" round. I have 2 with dampers but very seldom damper the exhaust. I have oversize intakes on the firebox but once up to temp I have the intakes just barely open. Adjusting intake air seems to work better at controlling cooking temps for me but everyone has their own methods. Build your smoker and after you do a few cooks you will know what works best for you. Smokers are like their owners. Each one is different. Enjoy.

[smc51]

on my reverse flow smoker, when it's hot and smoking meat, I only have my intakes open about an inch on each side of the firebox.

[brisket envy]

OK, thanks.
Got the stack height figured out...

Now I have a tuning plate question.

I know each pit is different, but can someone give me a ballpark number for this:
What should be the length of the total of the tuning plates vs. the length of the cooking chamber?

That is, what percentage of the cooking chamber length should the total length of the tuning plates?

Is the total amount of 'space' between the tuning plates somehow related to the size of the opening between the firebox and cooking chamber"

What I am wondering, is, with a 7' chamber, do the plates even need to extend beyond about 5', since much of the smoke/heat will have dissipated by the time the it gets that far?

I'm thinking too many plates might stifle the flow.

[brisket envy]

Well, here is the progress so far.
I got sidetracked by the smaller pit you see in the picture. It is for my neighbor.
My helper (son) is adjusting the chain on the shop crane that I used to hoist it up to the proper height.
It is also sitting on a jack on top of my welding table.

See how low my welding table is? When you get old, you like to sit down to weld as often as you can;-)

Still a lot to be done, such as adding handles, cutting off extraneous pieces, adding door and racks in vertical, capping off the skid rails, etc., but I think I will finish up this weekend.

[brisket envy]

The big pit went home this week.
I did a seasoning/test burn, just to see how much this wood hog would consume.
I was very pleasantly surprised.
I started out with some kindling, then three wrist-sized pieces, and then a couple of 4" diameter sticks.
when they were about 1/3 coals, I put on one 6" piece.
With the air intake all the way open, the temp got up to 450 and 400 on the near grate, and far grate, respectively. I let it sit there for a while, and then closed the air inlet down to about 25% of wide open.
The cooker had gotten pretty well warmed up, and the temps at the grates came down to about 250 at the near grate, and 225 at the far grate, and 190 in the vertical chamber.
This was all without the tuning plates in! This senior citizen forgot to put them in before he started the fire:blush2:

This was a big surprise to me. I didn't think the seemingly undersized firebox would maintain that kind of heat without a raging fire going on.

Anyway, when the owner came to pick it up, he was so pleased with it, he offered me a third tank to help even out the deal.
Overall, I am happy with the deal, and ecstatic about how the pit performed on the test.

I had done a lot of work with tanks and pipe, back in my younger days, but this time, I had my limited tools, and a cramped garage.

Oh yeah, and it was built using my 140 amp Longevity stick machine, running 1/8 6011 and 3/32 7018. (I was too cheap to go out and buy a can of 1/8 7018)