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View Full Version : first project and yess its gonna be a reverse flow!



matt4467
02-27-2009, 07:22 AM
hi everyone I'm new to the pit building world and just finished my fire box its 48"X24". Yes its big but going to use it on a 250 gallon propane tank. Let me know what everyone thinks about it I'm a little concerned about the size of the size of the airflow, I hope its big enough.

Joneser
02-27-2009, 08:03 AM
Not sure if it's too little...I don't have any experience with big pits like that. It looks like it will be very nice!
Stop in to C'mon in and sit down to introduce yourself.
Glad to have you here!

Bbq Bubba
02-27-2009, 08:23 AM
IMO...WAY to big.
Cut it in half and you'll need twice the intake for a 250 gallon smoker.

TX Sandman
02-27-2009, 09:20 AM
Howdy, Matt! Welcome! Stop by the Come In & Sit Down forum and tell us a bit about yourself and your other equipment.

I don't have experience with big pits, especially building one, so I can't help. But I'm looking forward to seeing everything come together.

Lefty
02-27-2009, 09:58 AM
the only guy I know with a 250 gallon has a 30 x 30 square firebox but its older and not reverse fllow

peculiarmike
02-27-2009, 11:40 AM
I'm with Bubba - WAY too big.
From a CD I have on building smokers -

Large fireboxes have much more surface area than smaller fireboxes, so they dissipate more heat to the surrounding atmosphere than does a smaller firebox. (Heat which does not contribute to the actual cooking of the meat is simply wasted heat, which equals wasted wood.) After many trials and errors, it was discovered that a firebox only needs to be 16 inches tall and 16 inches wide, with lengths ranging from 18 to 24 inches.

The above firebox will handle your 250 gal. tank with no problem. I made mine 16" square by 21" deep. The other consideration is -

The key element in a horizontal smoker involves the sizes of the fire box air inlet, the smoke inlet into the smoke chamber, and the smoke outlet. The opening of each should be about 23 to 24 square inches or larger. Six inch outside diameter pipe has an effective opening of about 23.76 square inches, and five by seven inch rectangular tubing has an effective opening of about 29.25 square inches. Dampers are placed on the firebox air inlet and the smoke outlet in order to regulate the heat and smoke flowing through the unit.

The above will also be sufficent for your 250 gal. tank. The opening from the firebox into the smoke chamber has to be located below the cooking grates and the exhaust should be located the same, or even with, the cooking grates. You may need a "deflector" on the firebox to smoke chamber opening to allow control of flames entering the smoke chamber.
If you want info on ordering the CD ($15) (which I have NO connection to) send me a PM and I will get it to you. I highly recommend it, lot of good information, drawings, and explanations of why things are done the way they are. And you get a BUNCH of recipes with it.
And it might make you rethink reverse flow.
Whatever you do, keep us posted on your progress. :msn-wink:
:twocents:

matt4467
02-27-2009, 12:13 PM
Me and my wife do a few fundraisers a year and when we cook we usually cook beteen 15 and 20 briskets at a time and im up half the night babysitting the firebox so i want to beable to stuff it full of wood and get a good nights rest while the meat is smoking.That is why i decided to build it this big because ive seen the problems with the pits ive borrowed in the past. i was just wondering if the airflow hole will be big enough.

Joneser
02-27-2009, 12:43 PM
Personally, I'd be afraid of ruining meat by letting the fire get away....I have BBQOCD like that..I guess you could sleep with a remote thermo under your pillow....:D

Bbq Bubba
02-27-2009, 01:35 PM
Me and my wife do a few fundraisers a year and when we cook we usually cook beteen 15 and 20 briskets at a time and im up half the night babysitting the firebox so i want to beable to stuff it full of wood and get a good nights rest while the meat is smoking.That is why i decided to build it this big because ive seen the problems with the pits ive borrowed in the past. i was just wondering if the airflow hole will be big enough.

A larger firebox doesn't mean less fire tending, it just means more heat, and wasted heat at that!
No, your intakes aren't sufficent to operate a 250 gallon, especially if you go reverse flow, needs even more of a draft!

peculiarmike
02-27-2009, 04:04 PM
:whathesaid:

Gunslinger
02-28-2009, 04:07 PM
I would have built a square one. If it was too big, you could line it with fire brick to retain heat. However, you could always coat the inside with refractory cement and accomplish the same thing. But then if it is a mobile unit, you would probably crack the cement. I know a guy that lined his square firebox with brick and then lined that with steel. Kind of a box inside a box. This guy has awesome heat control and retention with this setup.
I had a small round firebox before I built the bigger, square one. I was convinced that my problems were the smallish firebox. Then I cut the outlet bigger and wallah, better heat control than ever. Still built the square one for different reasons and it works out fine.

matt4467
02-28-2009, 09:37 PM
Well today we got the doors of the pit cut out, framed in with the flat bar, hinges & handles done, then we added door stops. The fire box is not going to be on the side of the pit it will be centered on the backside and sitting below, it will be inset. Here are a few pictures of our progress from today.. And I hope y'all don't drool too much over the fancy handles, they are just one of the feminine touches that will be on it for my wife, she is the cook afterall. But the best part about the handles.. they were only $1.99 each :msn-wink: Now I just need a few opinions on where to put my stack.

jerry516planes
03-02-2009, 01:05 AM
I just finished my smoker and the size of the firbox I used is 16 x 17 by 20 long. I used the following ratio calculator for the airflow calculations. I am very satisfied with the pits performance.

http://www.thesmokering.com/forum/viewtopic.php?t=20871


I also like a pit that is more self regulating and requires less tending. With the size pit that you have I would really consider lining the fire box with 2" of mineral wool insulation like the stumps smokers use. This is pretty simple. Build a frame of 2" box tubing on the outside of your box. Insulate around the outside and add a skin of 14 gauge steel to protect the insulation. Build the door the same way. Use some gasket rope and glue in place with RTF high temp silicon adheasive to seal up the door openings. You can get that at most any automotive supply store. The red works best for temperatures over 600 degrees.

I get longer burns using a basket made of expanded metal (9 gauge. I fill the basket full of charcoal and wood. Light it in one corner at the front. Let it burn and get up to temperature then damp down the fire to maitain your desired temperature and then fire will last for several hours. With my old smoker I had it down so that the fire would last 6 hours no problem.

With the king size fire box that you have you can also do a daisy chain fire.

I recommend watching the entire video as follows:

http://meadowcreekbarbecue.com/links.html

This should give you some ideas to help with your design.

matt4467
03-17-2009, 06:16 AM
Well been at work on the boat foir 2 weeks I'll be back home today. Cant wait to start on the pit this week. I should have the pit and fire box on the trailer I might need some advice on how to figure out how to connect them since they are both round how do i get the cut right? any help would be nice.