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


New RF smoker questions

 
Post new topic   Reply to topic    The Smoke Ring Forum Index -> Cookers
View previous topic :: View next topic  
Author Message
HeavyD
Newbie


Joined: 29 Jul 2008
Posts: 37
Location: Michigan

PostPosted: Wed Mar 03 10 1:31 am    Post subject: New RF smoker questions Reply with quote

I have a air tank I want to build a RF smoker from. Its 48" long by 20" dia. pipe. Would a 20"X16"X16" FB be the right size? I know the exhaust pipe needs to be at grate level, about how long of total exhaust pipe length would I need? I have some access to 6" and 8" pipe for the exhaust.

Thanks,
Heavy
Back to top
View user's profile Send private message
Jarhead
BBQ All Star


Joined: 11 Oct 2009
Posts: 7355
Location: Marionville, Home of the White Squirrels, Missouri

PostPosted: Wed Mar 03 10 2:03 am    Post subject: Reply with quote

Have you tried this yet?
http://www.thesmokering.com/forum/viewtopic.php?t=20871
Punch in your numbers and that should help you with a decision. It don't have to match exactly, only as a guideline.
_________________
Gunny 3073/4044/8411

Jarhead's World Blog
KCBS CBJ & HMFIC Debbie's Q Shack
Back to top
View user's profile Send private message Send e-mail
Jarhead
BBQ All Star


Joined: 11 Oct 2009
Posts: 7355
Location: Marionville, Home of the White Squirrels, Missouri

PostPosted: Wed Mar 03 10 2:14 am    Post subject: Reply with quote

I punched in your #'s
Your cooker is 12,058 cu in and your fb is 5,120 cu in.
Looks good there, 1/3 or larger.
Firebox air inlet opening needs to be 15.36 sq in
Firebox to cooker needs to be 40.96 sq in
Chimney:
6" = 9.06"
8" = 5.10"
4" = 20.38"
The first two seem kind of short if you vent at grate level. Others with more experience need to jump in and give it your best shot.
_________________
Gunny 3073/4044/8411

Jarhead's World Blog
KCBS CBJ & HMFIC Debbie's Q Shack
Back to top
View user's profile Send private message Send e-mail
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 26004
Location: Southeast Texas.

PostPosted: Wed Mar 03 10 11:47 am    Post subject: Reply with quote

HeavyD, your exhaust does not necessarily need to be at grate level. That is just where some people choose to place them.
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
Jon D. Q.
BBQ Super Fan


Joined: 12 Nov 2008
Posts: 404
Location: Middle Tennessee

PostPosted: Wed Mar 03 10 8:28 pm    Post subject: Reply with quote

I would put a 4" inside diameter exhaust on it. Sticking up above the top of the cooking chamber 19 1/2 inches. Just my 2 cents worth.
Back to top
View user's profile Send private message
HeavyD
Newbie


Joined: 29 Jul 2008
Posts: 37
Location: Michigan

PostPosted: Wed Mar 03 10 9:30 pm    Post subject: Reply with quote

K.A.M. I thought you have to have the exhaust at grate level so the hot air flow will be at the grate where your meat is? Question
Back to top
View user's profile Send private message
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 26004
Location: Southeast Texas.

PostPosted: Thu Mar 04 10 7:13 am    Post subject: Reply with quote

HeavyD, I hope not because there is a lot of reputable builders out there that are doing it wrong. Keeping the stack at grate height is a great mod that a lot of people use on chargrillers because they leak like a sieve and there are some builders that do bring the stack down to grate level because that is the way they feel there cookers perform best. But I do not buy into the fact that it is better than having your stack at the top of your cooker. I have built them both ways and have never found a significant difference to sway me either way.
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
Alien BBQ
BBQ All Star


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

PostPosted: Thu Mar 04 10 10:48 am    Post subject: Reply with quote

K.A.M. is right on the stack placement. It depends on how you plan on using your smoker. On smaller smokers it is a mod that helps most (not all) of the time to fix design flaws. There are plenty of smokers on the market that are designed both ways and work perfectly fine. It really does come down to how much you want to monkey with getting things consent and how OC you are about it. Very Happy Very Happy Very Happy
_________________
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
HeavyD
Newbie


Joined: 29 Jul 2008
Posts: 37
Location: Michigan

PostPosted: Fri Mar 05 10 11:02 pm    Post subject: Reply with quote

Those figures for the length of exhaust pipe sure doesn't sound long enough to me Question
Back to top
View user's profile Send private message
HeavyD
Newbie


Joined: 29 Jul 2008
Posts: 37
Location: Michigan

PostPosted: Sun Mar 07 10 11:27 pm    Post subject: Reply with quote

OK, so let me ask this, Can one's exhaust stack be to long or to big?
Back to top
View user's profile Send private message
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 26004
Location: Southeast Texas.

PostPosted: Sun Mar 07 10 11:32 pm    Post subject: Reply with quote

HeavyD, I think you can have to long a stack and also to large a stack. The stack being to large can be handled by a damper to choke it some.
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
seattlepitboss
BBQ Pro


Joined: 28 Oct 2008
Posts: 573
Location: Seattle, Washington

PostPosted: Mon Mar 08 10 12:40 am    Post subject: Reply with quote

HeavyD wrote:
OK, so let me ask this, Can one's exhaust stack be to long or to big?


My thinking is that the hot air flows up the stack because heat rises. Now think of a "piece" of hot air in the stack. If it moves up, there would be a vacuum behind it if more air didn't take its place. So more air gets pulled up the stack by the motion of the air going up the stack.

If the stack is too narrow, there is too much resistance to flow and the air can't get out quick enough - stale smoke.

If the stack is too wide, the rising air moves too slowly to effectively pull more air out - stale smoke.

The longer a stack with moving air in it is, the more momentum (energy) is in the moving air to pull air out of the smoker, out of the firebox, and ultimately into the firebox's air intakes.

So I see it as a design balance. If you are a HVAC engineer, you know how to calculate all this stuff, more likely there would be handbooks where you could look it all up. For the rest of us, we approximate and tune things with dampers. There isn't a fix for a too-small stack, though. I know a guy who made a smoker out of an air tank which had 2" threaded fittings at each end of the top. He just threaded pipe in there and used those for stacks. Never worked right. Too small.

Seems to me if a stack is too long, the air would cool by losing heat via convection out the sides of the stack, and the cold air at the top might get heavy enough to counter the force of the hot air coming up from below, fouling up the air flow. Stale smoke.

The good thing is that we don't have to reinvent the wheel. Guys on this and other forums have built good cookers out of about everything you can dream of, and you can just do what they did and it should work out about the same. On my current build, a 24x70" horizontal, I'm planning to use two 4" stacks each about 27" long. With dampers. Smile

seattlepitboss
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 All times are GMT + 8 Hours
Page 1 of 1

 
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