Design using the pit calculator questions

[Enrgizerbunny]

Hey guys I joined here a while ago and still haven't built my smoker. Life happens. I wore out my cheap grill with a side box, then acquired a pellet smoker which started having fires in the pellet hopper, so that was replaced with a propane grill. My wife loved the convenience of the pellet grill so she chose the propane route so that she can grill when I'm at work. So it forces me to get a real smoker.
Good news is that now it will be trailer mounted so I can take it to parties!

I'm getting back at the design now and I have a few questions about the pit calculator.

When it gives a firebox calculation, is that the area that I should be able to build a fire within or just the overall firebox?
For example: I want to design a firebox that has an elevated grate so that the ash will fall down and make it easy to remove from below as the fire burns. Should the area above the grate be equal to the firebox number?

The throat: My design is to take a rectangle 24x24x48" and set it canted 90 degrees so that it sits like a diamond. The throat will simply be a plate of steel welded into the "V" created in the bottom. I should have the throat area match the pit calc (or very close) at the firebox AND inside the cook chamber, right?

I've also noticed some variance in the calculator even when it seems I enter the same numbers. Does anyone know the reason for this?

[hogaboomer]

The grate has no effect on the firebox dimensions.

[dacolson]

The only variance in the throat dimensions should come from changes to how big your fb is. The bigger your FB, the bigger your throat.


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[Big T]

[Enrgizerbunny]

The grate has no effect on the firebox dimensions.

So even though the grate will reduce the amount of space that I can use to build fire, that reduced space doesn't affect anything? Therefore the firebox is more for proper flow and limiting combustion than amount of fire you can build? Am I getting that correct?

[dacolson]

You’re on the right track. You’ll find fire size will be a lot smaller than you might assume. The larger the FB, the more airflow you’ll need to get clean burns and good heat distribution and the harder it will be to get consistent temps. Too small and you end up trying to build a bigger fire to get it up to temp with not enough airflow and dirty fires. Check out Frank Cox’s write up here:

https://www.smokerbuilder.com/so-talkin ... ebox-size/


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[Enrgizerbunny]

You’re on the right track. You’ll find fire size will be a lot smaller than you might assume. The larger the FB, the more airflow you’ll need to get clean burns and good heat distribution and the harder it will be to get consistent temps. Too small and you end up trying to build a bigger fire to get it up to temp with not enough airflow and dirty fires. Check out Frank Cox’s write up here:

https://www.smokerbuilder.com/so-talkin ... ebox-size/


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Thanks. That post was helpful. Guess I'll have to add a slide to restrict my baffle plate gap for tuning. How does a 90 in the stack change things?

I've attached my dimensions as best I could capture. The fire box and intakes are both at 104.17%. The throat I have designed is a shade under size at 76.5 instead of 76.8.

Also added pictures of my crude drawing.

[dacolson]

A 90° in the stack is fine. Remember to measure stack height from the top of your CC.


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[Enrgizerbunny]

A 90° in the stack is fine. Remember to measure stack height from the top of your CC.


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Didn't know that. Thank you.

[Dirtytires]

I see you have a "drip pan" in your plans. With a reverse flow it is really not necessary...tho up to you if you want. The drippings hit the baffle plate and 'steam off' which creates great moisture and flavor in the cook chamber. After the cook, it takes about 2 minutes to scrape off any burnt pieces and wipe it down with a paper towel. I use a 6 inch putty knife to scrape and scoop.

[dacolson]

Also, you’ll want your drain to come from your BP through the bottom.


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[Enrgizerbunny]

I put the drain in the design for easy cleaning with a hose. I just want to minimize the drippings hitting the BP and inside the chamber to reduce cleaning. I think I'm going to use some aluminum cookie sheets to cover the BP instead. They're cheap and they fit in a standard dishwasher for easy cleaning the bulk of it.

For the rest I can lower the tongue of the trailer so it drains and then clean with soapy water and a brush and rinse with the hose.

[Enrgizerbunny]

Also, you’ll want your drain to come from your BP through the bottom.


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I don't understand what you mean. As of now it'll be below the baffle plate opening and lower than the throat opening.

[dacolson]

Also, you’ll want your drain to come from your BP through the bottom.


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I don't understand what you mean. As of now it'll be below the baffle plate opening and lower than the throat opening.

Lots of folks, myself included, put a dam at the gap end of the BP to keep grease from going over the edge to the bottom of the CC and then potentially running into the fb creating a grease fire. To make clean up easier, we’ll cut a hole through the baffle at that end of the BP and one below it in the bottom of the CC. I use a piece of 1.5” black steel pipe and run it up through both holes, weld it in place and put a 1.5” ball valve on the end. Makes clean up w a hose simple and keeps grease out of the bottom of the CC.


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[Enrgizerbunny]

For the baffle plate gap, the maximum gap should be the size of my throat with the ability to choke it down for tuning, right? (See picture)

[Enrgizerbunny]

Also, you’ll want your drain to come from your BP through the bottom.


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I don't understand what you mean. As of now it'll be below the baffle plate opening and lower than the throat opening.

Lots of folks, myself included, put a dam at the gap end of the BP to keep grease from going over the edge to the bottom of the CC and then potentially running into the fb creating a grease fire. To make clean up easier, we’ll cut a hole through the baffle at that end of the BP and one below it in the bottom of the CC. I use a piece of 1.5” black steel pipe and run it up through both holes, weld it in place and put a 1.5” ball valve on the end. Makes clean up w a hose simple and keeps grease out of the bottom of the CC.


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That makes sense enough. I was going to try making a low point to prevent it from getting in the firebox. The dam definitely sounds like a nice feature.

[Big T]

Yes, the BP gap should be no larger than the throat but can be up to 75% smaller, all though that seems a little tight to me.

[Enrgizerbunny]

I’m resurrecting this thread because I think I might actually get to build my smoker soon.

I am going back to the drawing board in terms of design, and doing away with the canted rectangle due to the reduction in useable space created by the angled walls, and instead building the same dimensions as two rectangle prisms.

My question is: does the throat count in the cooking chamber volume or should it be separate from the cooking chamber?

For example: if I build my CC according to the calculator and then place my throat within the chamber, aren’t I taking out that space (in reverse flow) from the CC and reducing the volume?

[Pete Mazz]

Unless it's way into the CC I wouldn't worry

[Big T]