FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 


Pit building ratio calculator
Goto page Previous  1, 2, 3, 4, 5, 6, 7, 8, 9  Next
 
Post new topic   Reply to topic    The Smoke Ring Forum Index -> Cookers Stickys
View previous topic :: View next topic  
Author Message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Sat Mar 28 09 4:58 am    Post subject: Reply with quote

Good luck on your build! Don't forget to post pictures of the build.
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
skeels01
Newbie


Joined: 07 Apr 2009
Posts: 50
Location: Wendell, NC

PostPosted: Tue May 05 09 11:52 pm    Post subject: Reply with quote

I ran my numbers through the calculator, and it says I need a chimney 6" diameter by 28" long. Is the 28" a minimum dimension? Can I go a few inches longer, just no shorter than 28?

Thanks!

John
Back to top
View user's profile Send private message Yahoo Messenger
Alien BBQ
BBQ All Star


Joined: 12 Jul 2005
Posts: 5422
Location: Roswell, New Mexico

PostPosted: Wed May 06 09 12:49 am    Post subject: Reply with quote

The calculator uses approximates based on prior reader input.
_________________
https://www.linkedin.com/in/michaeloberry
Back to top
View user's profile Send private message Send e-mail Visit poster's website Yahoo Messenger
skeels01
Newbie


Joined: 07 Apr 2009
Posts: 50
Location: Wendell, NC

PostPosted: Wed May 06 09 1:20 am    Post subject: Reply with quote

Alien BBQ wrote:
The calculator uses approximates based on prior reader input.


Thanks!
Back to top
View user's profile Send private message Yahoo Messenger
snappybob
Newbie


Joined: 06 May 2009
Posts: 25
Location: San Antonio, Texas

PostPosted: Thu May 07 09 4:03 am    Post subject: Reply with quote

I was just going to ask the same thing. Where do the formulas in the spreadsheet come from? Did someone do some sort of analysys to get the best flow through the pit and come up with these ratios?
Back to top
View user's profile Send private message
SPM



Joined: 06 May 2009
Posts: 7

PostPosted: Thu May 07 09 4:50 am    Post subject: Reply with quote

For some reason (probably I'm an idiot) I can't plug in the numbers. I'm using the google account. Does someone know where I'm going wrong? Also this site is fantastic. I've already told everyone I know that smokes about it. Thanks, SPM
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Thu May 07 09 3:06 pm    Post subject: Reply with quote

SPM,

To be able to use the Google calculator you have to have a Google docs account, its free to sign up.


snappybob,

The ratio formulas are the work of Mike (Alien BBQ); I just put them in the spread sheet.

Good luck with the builds!
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
SPM



Joined: 06 May 2009
Posts: 7

PostPosted: Fri May 08 09 5:08 am    Post subject: Reply with quote

Thanks Tom, I did sign in though. I'll try again. SPM
Back to top
View user's profile Send private message
SPM



Joined: 06 May 2009
Posts: 7

PostPosted: Fri May 08 09 8:07 am    Post subject: Reply with quote

Well it worked this time. Thanks again, SPM
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Fri May 08 09 12:58 pm    Post subject: Reply with quote

SPM,

Glad to hear it worked for you. Good luck on the build.
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
snappybob
Newbie


Joined: 06 May 2009
Posts: 25
Location: San Antonio, Texas

PostPosted: Fri May 08 09 11:49 pm    Post subject: Reply with quote

I roughed out a design based on the spread sheet. Below is a pic of what I wound up with. Looks pretty good to me. Here are the numbers.

Cooking Chamber 24"Dia. X 36L
Fire Box Volume 5694 CI
Fire Box Air Intake Area 45.38 SQ In
Fire Box to Cooking Chamber Area 132 SQ In
Exhaust Stack 5" Dia. X 41.5 Length

Did I decipher all the numbers right. I made the fire box a little larger than called for because I figure I'll probably put a plate in the bottom that will take up some room.

I know, it's got a funky paint job. Rolling Eyes The different colors make the components stand out a little better.

Anybody have any suggestions or comments?

Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Sat May 09 09 2:07 pm    Post subject: Reply with quote

snappybob,

Your firebox size looks fine but it looks like you used your cooking sections volume to figure your opening and smoke stack numbers.

You need to use the firebox volume in the calculator. I got numbers much smaller on the openings and stack length based on your firebox volume of 5694 ci.

Firebox air intake area: 17.08 SQ In.
Firebox to cooking chamber area: 45.55 SQ In.
Smoke stack 5 dia. X 14.51 inches in length.

I would use 4 dia. pipe for the smoke stack and then it comes out to 22.67 inches in length or even 3 for 40.3 inches in length.

Let me know if you have any questions.
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Sat May 09 09 2:23 pm    Post subject: Reply with quote

Everyone,

I had to update the link to the calculator site on my original post. If you have saved the location as a favorite in the past the link will no longer work. Sorry for any problems this may have caused. The new link appears to work fine.

Also you will notice that the link to the MS Works spreadsheet is no longer listed on the web page. It was not working correctly so I removed it.

Tom C.
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
snappybob
Newbie


Joined: 06 May 2009
Posts: 25
Location: San Antonio, Texas

PostPosted: Sun May 10 09 3:13 am    Post subject: Reply with quote

Thanks Tom, I thought the air intake to firebox and opening from the firebox to the main chamber looked rather large. That expains it. I'm glad I put my design out there for a sanity check. These changes are easy to make at this point. That's a great calculator. Thanks for sharing that with us.
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Sun May 10 09 3:46 am    Post subject: Reply with quote

You're welcome. Glad to help.
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
SPM



Joined: 06 May 2009
Posts: 7

PostPosted: Sun May 10 09 10:19 pm    Post subject: Reply with quote

Hey Tom, I have a few questions for you and whoever is familure with the calculator. Is it ok for my firebox to be half the size instead of a third? Also the calculator says I need a firebox to chamber opening of 57, when I scroll down it give me an opening of 157. Do I make it bigger or try to achieve 57. My dimensions are: fire box is 18"x22" dia, chamber is 36"x22" dia, and I have a 4" stack. Thanks, SPM
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Mon May 11 09 5:10 am    Post subject: Reply with quote

Hi SPM,

You can be bigger for your firebox. Mine is almost half and works fine. It just means more material and bigger openings to get airflow.

On the calculator remember that if you enter dimensions for a circular firebox you need to look in the blue cells for all your results.

If I'm following you correctly, you entered 22" dia x 18" length for a circular firebox.

When I enter this size I get the following:

Air inlet to firebox = 20.52 sq.in
Firebox to cooking chamber =54.71 sq.in
4" dia pipe length needed = 27.23

For the firebox to cooking chamber opening I entered 7.8" by 7" to get the volume as close to the 54.71 listed above. The calculator showed that 7.8" x 7" = 54.6 sq. in. the calculator indicated that I would only need 1 opening of that size indicated in the blue cell to the right.

You can change the dimensions of the opening to anything that will fit for you but you need for the blue cell on the right to indicate the need for 1 or slightly less than one for the opening to be big enough.

Example:

Instead of 7.8" by 7" you could enter 7" by 9.25" and the calculator indicates that you need .99 or one of these openings.
This allows you to change the opening size around to best fit your needs but still make sure you have the correct opening volume needed for airflow.

Hopes this helps

Tom
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
SPM



Joined: 06 May 2009
Posts: 7

PostPosted: Tue May 12 09 5:23 am    Post subject: Reply with quote

Tom, you're golden brother. You answered everything I needed to know. Now I can get to cutting and welding and maybe some smoking by June. Thanks a bunch, SPM.
Back to top
View user's profile Send private message
Tom C
BBQ Super Pro


Joined: 21 Jul 2007
Posts: 1851
Location: N. California

PostPosted: Tue May 12 09 12:53 pm    Post subject: Reply with quote

Thank's SPM and good luck with your build. I'm looking forward to some pictures. Very Happy
_________________
Homemade offset smoker 24"x48"
Charbroil CB900 grill
Back to top
View user's profile Send private message
snappybob
Newbie


Joined: 06 May 2009
Posts: 25
Location: San Antonio, Texas

PostPosted: Fri May 15 09 1:13 am    Post subject: Reply with quote

Does this look a little better?



I think so. Here are the numbers I wound up with.

Fire box vol. = 5740 cu in
Inlet Air = 18 sq. in
Air to Main chamber = 49.56 sq in
Stack Dia X L = 4 X 22.83

I am assuming that the stack length is the circumference of the elbow center line and the straight section combined.

Also, how important is the position of the stack on the end cap. Is near the grill better than near the top or vice versa?
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    The Smoke Ring Forum Index -> Cookers Stickys All times are GMT + 8 Hours
Goto page Previous  1, 2, 3, 4, 5, 6, 7, 8, 9  Next
Page 2 of 9

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2002 phpBB Group