Pit Building Ratios

Tom C · Posted: Jun 21 2008 Post subject:

Your welcome HillbillySmoker, I received lots of help here when I working on my smoker, I happy to be able to do the same for others now.

It sounds like you hav a good working plan. You should be able to make adjustments if needed without too much problems. I'm looking forward to seeing the progress pictures! Very Happy

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Homemade offset smoker 24"x48"
Charbroil CB900 grill

firefighter · Joined: 30 Apr 2008 Posts: 17

When you have a chuckwagon type of smoker, do you take the sum of the cooking volume and the smoke chamber volume to calculate the chimney?

Tom C · Posted: Jul 14 2008 Post subject:

You use the size of the firebox to calculate the chimney size in a standard offset smoker. I'm not sure I know that type of equipment your refering to. I'm sure someone else here knows that style. Could you post a picture or give an example to enlighten me?
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Homemade offset smoker 24"x48"
Charbroil CB900 grill

firefighter · Joined: 30 Apr 2008 Posts: 17

This is the type I'm talking about

Tom C · Posted: Jul 15 2008 Post subject:

In that type of smoker I would have just a small stack coming out of the vertical section just as pictured. You should get plenty of draft with a vertical section like that.
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Homemade offset smoker 24"x48"
Charbroil CB900 grill

diatri · Newbie Joined: 01 Mar 2008 Posts: 41

OK, I've tried to use the different spreadsheets, but it is late and I can't get it. Can someone help me?

I have a pipe that is 5 feet long and 36 inches in diameter. The firebox is going to be 36 inches by 36 inches.

How big should my opening to the cooking chamber be? And how big should the air intake be on the firebox? From what I can figure, the stack should be about 3.75 feet tall. Any help is appreciated.

Tom C · Posted: Aug 29 2008 Post subject:

Wow! That's going to be a good size smoker! A 36x36x36 firebox is going to require a large smoke stack.

Based on the ratios listed here, you will need the following:

140 sq. in. for your air intake.

373.25 sq. in. going into the cooking chamber.

You may want to think about duel stacks. The calculation I get for stack is pretty big depending on the size pipe you use. I calculated using a 6" pipe and it came out that one stack would need to be nearly 7 feet long at 6.87'.

One way to change that would be to make the firebox smaller. I would think about changing the length to 24" and maybe the height to 24" as well. Just by doing that would change the numbers to the following:

62.21 sq. in. for your air intake.

165.89 sq. in. going into the cooking chamber.

4.4 feet for the smoke stack using 5" pipe.

I would think that would work well and save you some material as well. I can re-run the calcs for any variation in firebox size you like. Others here I think would agree that the firebox could be smaller and still work fine.

I hope this helps.
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Homemade offset smoker 24"x48"
Charbroil CB900 grill

HeavyD · Newbie Joined: 29 Jul 2008 Posts: 37 Location: Michigan

Going to build a big ol smoker, 36"dia. x 10' long. Its a old propane tank that I have and want to do a reverse flow smoker. I'm thinking of a 36x30x30 firebox, what would my air intake need to be? I have a 6" pipe for the exhaust stack, how long would that need to be? How far off the cooking surface do the stack need to be? Confused

Thanks in advance

HeavyD

Tom C · Posted: Aug 29 2008 Post subject:

On that size firebox (36x30x30) I come up with the following:

97.2 sq. in. For the air intake

259.2 sq. in going into the cooking chamber

57.2 inches of 6inch pipe needed for the smoke stack

You will want to bring the smoke stack down as close as you can to cooking grate level.

Good luck with your build!
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Homemade offset smoker 24"x48"
Charbroil CB900 grill

diatri · Newbie Joined: 01 Mar 2008 Posts: 41

Tom, thanks for helping out. That is some of the numbers that I was coming up with, but thought I had to be doing something wrong. My brother-in-law is getting the pipe from a friend of his. I told him the firebox would be better at 24", but he said that it was already at 36". Maybe I can talk him into cutting a foot off of it and making a fire ring with the left overs.

HeavyD · Newbie Joined: 29 Jul 2008 Posts: 37 Location: Michigan

Thanks Tom, Was looking for any kind of information. I seen Aliens ratio's and was wondering about the length of exhaust stack = 3/4 lengh of smoker. That would make one long stack with a 10' long smoker. So your guestimating that a 6" pipe 6' long should do the trick taking it goes as close to the cooking surface as possible? Thanks a million.

HeavyD

Tom C · Posted: Aug 31 2008 Post subject:

You're welcome, I'm glad to help out. Looking forward to seeing pictures of your smoker build. Good luck and have fun with it.
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Homemade offset smoker 24"x48"
Charbroil CB900 grill

Tom C · Posted: Sep 01 2008 Post subject:

Back when I was making my smoker. I made up this Excel spreadsheet to help me with the calculations and tweaks to make it all work. All calculations are based on Alien BBQ's ratios.

All revelent data is entered in the yellow cells to get the calculations needed.
The tan cells show calcs for a rectangular firebox and the pink cells are based on a circular firebox.

I could send this to anyone that has MS Excel 95 or newer that would like to play with it. Let me know if you are using Excel 95 since this was made on Excel 97. I would have to save it differently before sending to you.

PM me with an e-mail address if you would like a copy of the file.

Comments for improvement are welcome as well.

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Homemade offset smoker 24"x48"
Charbroil CB900 grill