Problems with oxygen flow on my new offset smoker

Custom manufactured BBQ Pits, Do-it-Yourself projects, parts and ideas.

Moderator: TBBQF Deputies

Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Wed Jun 24, 2020 1:30 pm

Hello all ;-) , just joined a forum, greeting from Lithuania, i decedided to build my own offset smoker from scratch , everything done, but need help, having trouble with oxygen flow , it is very hard to start fire and even when logs are burning smoke trying to come out thruu back doors, i have no idea what i done wrong when i build it, i will upload few pictures and dimmension of it.
Can someone give some advice please.

Cooker Chamber size : Length 53.14 inch , diameter 23.62 inch
Firebox Dimensions : length 23.22 inch, diameter 23.62 inch.
Chimney Size : length 28.3 inch , diameter 3.9 inch.
Back door are made from 2 little doors first is : 7.87 by 6.6 and second 7.87 by 3.9 inch
Attachments
20200624_204307.jpg
20200624_200315.jpg
20200623_164232.jpg
20200624_200351.jpg
20200624_200346.jpg
20200624_195558.jpg
20200624_195536.jpg
k.a.m. USER_AVATAR
k.a.m.
Chuck Wagon
Posts: 3741
Joined: Mon Jun 25, 2012 6:38 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby k.a.m. » Wed Jun 24, 2020 2:33 pm

Welcome to the forum.
So you use the doors as intakes?
If so are both open or how do you run it?
Always remember slow and steady wins the race.



My Hybrid cooker.
Competition trailer #2.
hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Wed Jun 24, 2020 3:07 pm

Maybe the firebox to cook chamber opening is too small? Did you make it using a BBQ calculator?

Gonna be a lot of work trying to make that opening bigger, I believe I would try a bigger smoke stack (chimney) first.

Pretty unusual firebox door design. That's a pretty big smoker for such a small firebox door opening. I would want more room to be able to make my fire.

So, this smoker is close to yours in size, this is the firebox door. That was the first fire I made in it, that's why it's so big, I wasn't cooking on that much fire.


Image
Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Thu Jun 25, 2020 12:09 am

k.a.m. wrote:Welcome to the forum.
So you use the doors as intakes?
If so are both open or how do you run it?



Im using doors as intakes, then strarting fire both doors open, after 10 minutes close the bigger doors and leave little ones wide open. I tried to open both when its burning and the smoke start coming back thruu. When logs finished to burn visible leak on the inside of the chimney
Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Thu Jun 25, 2020 12:25 am

hogaboomer wrote:Maybe the firebox to cook chamber opening is too small? Did you make it using a BBQ calculator?

Gonna be a lot of work trying to make that opening bigger, I believe I would try a bigger smoke stack (chimney) first.

Pretty unusual firebox door design. That's a pretty big smoker for such a small firebox door opening. I would want more room to be able to make my fire.

So, this smoker is close to yours in size, this is the firebox door. That was the first fire I made in it, that's why it's so big, I wasn't cooking on that much fire.


Image




I just tried to use fendon's bbq calculator , thats what i get:
Link to BBQ Pit Calculator


The fire box doors i will fit bigger ones , as recommended 19.29 square inch.
It shows my firebox size is 10174 and recommended 7757. Size differential is 131.2%

At the moment chimney diameter is 3.9 inch , length is 28.3 inch, what diameter pipe you can recommend and whats the length have to be ?( what diameter is the picture above?)

And the chamber opening i will post the picture , dont now how to calculate it? I done it without any calculation , just saw picture in google and build it
Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Thu Jun 25, 2020 12:27 am

Firebox-to-chamber opening , thats what i got
Attachments
15930627758458728394731100700147.jpg
hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Thu Jun 25, 2020 6:06 am

Mattt85 wrote:Firebox-to-chamber opening , thats what i got
How wide is it? According to Feldon's pit calculator, you need about 83 sq. inches of throat opening. The cook chamber opening is the last one on the list in the Feldon's page. I'm no math expert and don't really know how to figure the area of your opening, but it doesn't look like 83 sq. inches. If you had a 6 inch tall rectangle, it would need to be 14 inches wide.


My chimney is 6 inch pipe. Feldon's say your 4 inch chimney needs to be 42 inches high.

I hate to say it, and I'm no expert builder, but according to Feldon's, it looks like you need to cut the firebox off and raise it up some, to make the hole bigger. That's why I said try a bigger chimney first.

Hopefully k.a.m. can come up with an easy solution. He knows more about all this than I do.
Last edited by hogaboomer on Thu Jun 25, 2020 6:33 am, edited 1 time in total.
Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Thu Jun 25, 2020 6:21 am

14.57 inch wide
Attachments
15930840428528634296915395447035.jpg
hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Thu Jun 25, 2020 6:36 am

hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Thu Jun 25, 2020 6:43 am

So, you did all the calculations. It says 14.5 inch diameter half moon, that would be 7.25 inches high with the top of your opening being a straight line. Your top curves down with the pipe contour, and it's only 5.9 inches at the highest point.
Mattt85
Pilgrim
Posts: 16
Joined: Wed Jun 24, 2020 12:33 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby Mattt85 » Thu Jun 25, 2020 7:08 am

Looks like i have to make smaller firebox, just cit it round and make shorter, then inside opening will be right size...
hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Thu Jun 25, 2020 7:28 am

You need a bigger hole, not a smaller firebox. Did you weld it on the inside?

If it was me, I would cut the firebox off and raise it up some. And re-work the firebox door while I had it cut loose.


edit: I put the numbers in at 18 inch long firebox, gets you to 101%, needing a 12.67 inch diameter half moon. So, that gets you close on your opening size. It won't be as high as it should, but it's wider than needed, so maybe that offsets. I guess it's worth a try, if it's easier than cutting the firebox off and raising it.

Good luck, and keep us posted. This forum needs more traffic.
k.a.m. USER_AVATAR
k.a.m.
Chuck Wagon
Posts: 3741
Joined: Mon Jun 25, 2012 6:38 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby k.a.m. » Thu Jun 25, 2020 9:15 am

This is what your football opening should be.
Overall Height of cut-out
6.849
Cut-out Width
16.375
Calculated Throat Area
77.32
You have two options here.
1. Cut the firebox loose and raise it 3". Once this is done leave 1" at the bottom for a grease bridge and cut the top section of the football opening 2" taller.
2. Cut the top of the firebox and cooker wall where they mate then box it in. You will need to cut up 2" on the wall and the width of your half moon and 2" and down to your connecting points into the firebox. This new opening will increase your firebox to cooking chamber opening.
Note: My preference is #1.

You need a larger exhaust. 6" x 24" tall would be my preference.
In the event that is not doable cutting your existing 3.9" down to 24" and adding a second would give you the flow needed.
Always remember slow and steady wins the race.



My Hybrid cooker.
Competition trailer #2.
hogaboomer USER_AVATAR
hogaboomer
Rustler
Posts: 174
Joined: Tue Jun 11, 2019 9:42 pm
Location: Groves, TX.
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby hogaboomer » Thu Jun 25, 2020 9:38 am

How does one calculate the area on a football cut, Kevin?
k.a.m. USER_AVATAR
k.a.m.
Chuck Wagon
Posts: 3741
Joined: Mon Jun 25, 2012 6:38 pm
Contact:

Re: Problems with oxygen flow on my new offset smoker

Postby k.a.m. » Thu Jun 25, 2020 10:04 am

hogaboomer wrote:How does one calculate the area on a football cut, Kevin?

A tool created by an old friend on another forum I am on.
https://planetcalc.com/5155/
Always remember slow and steady wins the race.



My Hybrid cooker.
Competition trailer #2.

Return to “Custom Built Pits, Build Your Own Pit & Pit Modifications”

Who is online

Users browsing this forum: No registered users and 16 guests