Firebox questions

[Dirtytires]

Are you saying your firebox is only at the 53% mark? If this is the case, I would strongly recommend you re-size it before you go any farther. That small of a box will result in a cold and hard to maintain pit that is absolutely no fun to operate.

Yea, it's no fun, but definitely easier to fix now than to have to do it later.

[SheffSmoker]

You may have trouble getting your pit hot enough. How much too small are you talking about?

47%

You sure you are using the correct units? an 118" long CC is almost as long as my car!

[D . Jur]

You may have trouble getting your pit hot enough. How much too small are you talking about?

47%

You sure you are using the correct units? an 118" long CC is almost as long as my car!

Unfortunately, yes, I'm sure. CC realy 118 inches is 3 meters in our metric units.
In gallons, that's 528 by volume.

[SheffSmoker]

Wow! She's a beast!

[D . Jur]

Yeah! But not she. I call him Monster Joe!
Of course, it may not be beautiful, but it works. Of course there is a lot of fuss with him in the process ... which we will eliminate.

[Big T]

I think Monster describes it pretty well!

[Kcd2016]

That stack is a monster too. Did you use the calculator?

[D . Jur]

That stack is a monster too. Did you use the calculator?

No. Then (more then year ago) I did not know about this forum yet ...
Stack 8.1 "in diameter. How important is its length?

[Dirtytires]

All the volumes of a pit are important. It might make sense to run the numbers off the pit calculator and then compare it to what you have. With an undersized firebox and an oversized chimney, I would expect a really cold running pit...especially at the chimney end of the pit. When all the parts are in the proper ratio (firebox size, cook chamber size, throat, chimney and intake), everything will run much easier.

[Dirtytires]

But to answer your question, it's the volume of the chimney that is important, not the diameter. You can easily cut it down in length to get to the proper volume. As it sits, I would guess you are about double what is recommended.

[D . Jur]

All the volumes of a pit are important. It might make sense to run the numbers off the pit calculator and then compare it to what you have. With an undersized firebox and an oversized chimney, I would expect a really cold running pit...especially at the chimney end of the pit. When all the parts are in the proper ratio (firebox size, cook chamber size, throat, chimney and intake), everything will run much easier.

You are absolutely right that the coldest point is right at the exit from the CC.
Here, yesterday I filmed a video.
https://youtu.be/hCKswKs0Hi8
That is why I want to fix all of this to make it easier to work.

[D . Jur]

But to answer your question, it's the volume of the chimney that is important, not the diameter. You can easily cut it down in length to get to the proper volume. As it sits, I would guess you are about double what is recommended.

I entered the stack diameter, 8 "into the calculator and it returned this ...

[D . Jur]

what does this 19.46 mean? Match line shows 100% ...
The stack is now 8 "wide and 130" high, just above the center of the CC.
The stack goes through the roof of the garage to the street, which is why it is so long.

[dacolson]

The calculator is over compensating for your FB size. If you plug your tank volume in, I get a FB that’s 35”x35”x35” and a stack with and 8” diameter at roughly 27” from the top of your pit. If you want to go higher, you need a smaller diameter stack. A 5” outside diameter x 1/4” wall pipe would get you 121”. You could stretch it to 130”. I have no idea if that much height would be a problem but that doesn’t seem too excessive.

[tinspark]

I haven't run the numbers to confirm, but as a cheap test, you could find some light gauge sheet metal duct ( we call it snaplock pipe here in the states) and drop it down the top of your larger pipe and seal it off inside your cc with a blank off plate, which is essentially a flat square 10x10 plate with a 5" hole fastened with screws. Just to do a few test burns only. If it works you could either rip out the nice stainless stack that you have, or just run a permanent smaller size inside the existing pipe. Of course you would want a thicker permanent pipe, but as a cheap test......??. .... just a thought
Here is a link to some galvanized (for testing only) light gauge duct. Might be able to find it cheaper locally or a similar option for a stack test..
https://www.amazon.com/DUCT-PIPE-GALV-3 ... 649&sr=8-3

[D . Jur]

I haven't run the numbers to confirm, but as a cheap test, you could find some light gauge sheet metal duct ( we call it snaplock pipe here in the states) and drop it down the top of your larger pipe and seal it off inside your cc with a blank off plate, which is essentially a flat square 10x10 plate with a 5" hole fastened with screws. Just to do a few test burns only. If it works you could either rip out the nice stainless stack that you have, or just run a permanent smaller size inside the existing pipe. Of course you would want a thicker permanent pipe, but as a cheap test......??. .... just a thought
Here is a link to some galvanized (for testing only) light gauge duct. Might be able to find it cheaper locally or a similar option for a stack test..
https://www.amazon.com/DUCT-PIPE-GALV-3 ... 649&sr=8-3

In my stack, there is a damper for adjustment, it is usually always 100% wide open, can I recreate narrow pipes with it, or is it not the same thing?

[tinspark]

No. By “create narrow” pipe you are saying just choke it down, It is not the same thing. You must get the volume right. Volume of stack is based off of CC volume (and FB size too for that matter). You might need to take the damper out if possible. Once things are sized properly, there is no need for a damper. The extra effort to get it flowing correctly will be worth it in the long run. Remember, it is only metal and metal can be modified.

[D . Jur]

Anyway, it is already clear that the FB is not large enough, so now you need to first increase it.
I will do this.

[D . Jur]

By the way, about the volume ... when the FB increases, do I need to take into account that part of the FB that is to the left of the dotted line? Because now she is not involved in the calculation.

[Dirtytires]

You typically do not want any part of the firebox below the cook chamber. Doing so just increases the radiant heat to this area and creates a hot spot. Best if you hang a new, properly sized firebox off the end.

[D . Jur]

Well, I lengthened the firebox.

Now, according to the calculator, everything is so.

Tomorrow I'll redo the stack, let's see how it all works.]

[towtruck]

Looking good so far.

[Big T]

[Dirtytires]

Moment of truth!

[D . Jur]

Well, after lengthening the firebox and shortening and narrowing the stack, everything works ... almost the same! Except for a couple of things:
1. There were errors when cutting doors and there are small leaks.
2. There is a hot spot, this is the middle shelf, in the middle of the CC.
3. The coldest shelf remained near the stack.

From the pros, a smoother cycle, I began to throw up the logs a little less often, before it was 15 minutes, now 20, sometimes 22-25 minutes. Temp is always between 250-275F.

The main question is the shelf at the stack! Will she always be the coldest? I watched several videos where it was said on the contrary, that this is the most "correct" shelf for cooking.
Or shouldn't temperature and convection be compared?