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firebox to cooking chamber opening

 
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dmike25
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Joined: 27 Dec 2009
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Location: Colorado Springs (sometimes)

PostPosted: Mon Feb 16 15 10:41 am    Post subject: firebox to cooking chamber opening Reply with quote

I've been building an offset cooker, 24" pipe 44" long. The firebox is 20"X20"X22" long. The chimney is 4"X36". It will have tuning plates. I've started building the firebox, and decided to check the fb to cc opening. I built the cooking chamber with a half moon opening and a 2" grease bridge.
The top of the opening is 4 3/4" below center. I just put my numbers into Feldons calculator, and discovered that the opening is too small, 64 sq. inches rather than the 70.4 the calculator suggests. Easy enough to fix, I'll just make the opening bigger. My question is how much bigger? As it is, I have a 2" grease bridge. If I open it up to 72 square inches it will be 2% big with a 1 1/2" grease bridge. If I leave a 1" grease bridge it will be 19% bigger. The calculator mentions that the grease bridge should be at least 1 1/2". I'm curious as to why so tall? I can't imagine there being so much grease in the bottom to breach a dam that's an inch tall, much less an inch and a half. I'm leaning towards making the opening 119%. What do y'all think?
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TrailerBuilder
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Joined: 08 Feb 2010
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Location: Springfield MO

PostPosted: Mon Feb 16 15 11:04 am    Post subject: Reply with quote

In all the cookers Ive built so far, I have just ran a 1" grease bridge. So far, I have not heard of anyone flooding that yet.
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k.a.m.
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Joined: 12 Dec 2007
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Location: Southeast Texas.

PostPosted: Tue Feb 17 15 12:59 am    Post subject: Reply with quote

If you do not forget to drain your cooker between a normal cook you can get by with a 1" bridge. If you look at the distance covered on the radius 1" in my opinion is not enough.
If you load your 24" x 44" with Butts or briskets I believe you will be close to crossing the 1" bridge in a single cook.
I prefer a 1.5" on smaller cookers but that is just me.
I hope this helps. Very Happy
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dmike25
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Joined: 27 Dec 2009
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Location: Colorado Springs (sometimes)

PostPosted: Mon Feb 23 15 7:26 am    Post subject: Reply with quote

Thanx Troy and Kevin. I"m going to build it with an 1 1/2" bridge. If it doesn't breathe well during the first couple of cooks, it wouldn't be too difficult to modify the opening at that point.I sure appreciate your input,
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seattlepitboss
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Joined: 28 Oct 2008
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Location: Seattle, Washington

PostPosted: Thu Mar 12 15 7:31 am    Post subject: Reply with quote

Does your smoker have a grease drain designed in? My horizontal copied one of KAM's designs. The RF plate slopes away from the firebox and at the far end the grease drains out a 2" pipe. I haven't ever worried about a grease dam and looking through my firebox with a flashlight, it doesn't look like any grease has ever gotten down there.

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k.a.m.
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Joined: 12 Dec 2007
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Location: Southeast Texas.

PostPosted: Fri Mar 13 15 7:05 pm    Post subject: Reply with quote

seattlepitboss wrote:
Does your smoker have a grease drain designed in? My horizontal copied one of KAM's designs. The RF plate slopes away from the firebox and at the far end the grease drains out a 2" pipe. I haven't ever worried about a grease dam and looking through my firebox with a flashlight, it doesn't look like any grease has ever gotten down there.

seattlepitboss

It isn't a matter of if it overflows it is a matter of when. The when is that time you are doing a huge cook and forget to open the drain during that cook. The reason I started implementing the bridge is because I started reading about grease fires in cookers of all types even reverse flow designs.
It is a simple add on that can save you hundreds of dollars in ruined meat. Wink
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