Firebox Size - How Big? Building Homemade Smoker

by Jason
(Jefferson City, Missouri)

I am building an offset smoker pit along with a friend. It's our first attempt and I have my design figured out along with the dimensions. It's 3'x5' WxL, and the cooking area for the racks is 28" tall. the chamber to carry the smoke from the firebox to the opposite side is 20" depth X 36" width and I'm leaving a five inch gap at the end for the smoke to travel.

Pit Smoker On Wheels

The chimney is on the firebox side about half way up in the cooking area. I was going to make my firebox 2' square. Now I was told by a guy that builds large charcoal grills and only two smoker pits that my firebox is to large. Is my fire box to big or small and the chamber that the smoke is going to travel is it to big?

Also there is a 10" overlap between the smoker and firebox, how big should I make the opening- all 10" or smaller? Thanks for reading and I really look forward to hearing from you. I would like to have it built before July 11th, my first sons first birthday! Oh yeah a big BBQ planned!

Determining The Firebox Size of a Homemade Smoker

Firebox Of an Oklahoma Joe Pit Smoker

fire box size
by: bbqjim

I've been working with smaller smokers so I can cart them around easier to cook offs and parties. I've found that 1/3 the size is good and I find that round fire boxes work better.

The flow of heat is more stable, because heat does not want to go sideways. It wants to go upwards. If it's square the heat traps in the top and with the vent air pushes it sideways. It's real hot then cool. I've tested this.

If you have a square box to work with put a hole in the top and use a 90 degree pipe fitting to the smoke chamber. Put the box on wheels and put a flue in the 90 deg pipe. Now you have 2 pieces to move. It's much lighter.  Put a pull handle on the box like a wagon.

Oh, if you use a round box you will need to put 2 more vents on each side below the grate in the middle, which works best.  The vent on the end just doesn't get it.

Happy smoking brothers

bbq jim,
8x grand champ with Bill Anderson bbq team

have a great day.

firebox size
by: chas

Rule of thumb. Firebox size should be 1/3 the volume of the cook chamber.

putting a sub floor
by: chipster

I was wondering about putting the metal floor at the highest point of the firebox so it has to travel all the way across both sides of the meat . i NEED some dos and don'ts about this idea. Your suggestions would greatly be appreciated. thanks

fire box on the side or behind?
by: Anonymous

I am building my very first smoker, what is your opinion regarding attaching the fire box behind and parallel to the smoke chamber? Will it work just as well as putting it on the sode perpendicular to the smoke chamber?

fire box
by: ray ray

I have a 250 gal smoker. How big does my fire box need to be

Flue not flew
by: Anonymous

The spelling is flue, not flew or fluke.

That's a Reverse Flow Smoker...
by: BBQ Mike

Hi Guys, sounds like you are building a "Reverse Flow" smoker with an offset firebox. It's a fantastic design for making great BBQ. Your fire box sounds like it would be big enough for the size cooking chamber that you will have.

But a rule of thumb that goes for a lot of things is "Bigger Is Better"... You can always control the temp with your dampers... By the way, it's a "flew" not a "Fluke" as someone put it.

Good Luck,

BBQ Mike

Aspiring Pittmaster
by: Anonymous

Why are you putting your fire box on the same side as your flue? I am thinking about putting my fire box on the same side but putting a sub-floor so that the smoke has to travel to the opposite side of the floor before traveling back to the fluke, for added smoke and heat distribution.

Homemade Smoker Firebox Size
by: Bill

It sounds like too large of a firebox sucks the heat out of a smaller fire before it can enter the smoke chamber. Interesting.

by: Bacnars Backyard BBQ


I just finished one that is about the same size. It over smokes the meat. Mine firebox is 24X24X24 and has a hard time maintaining a consistent temp without a huge fire. I believe 18X18X24 OR 16X16X24 is more than sufficient.

I will let you know how mine works after the modification. I have heard the firebox should be 30% of the main smoker!