Can't Get My Pit To Draft

by Mike
(South Carolina)

I can't get my pit to draft, please can you help?

I have a pit 24"x 24" by 1' deep at the top then it goes down in the ground approx 2 more feet at 16"x16". Making it about a total of 3' deep.

It is lined in the bottom with fire bricks. It has a 2"x 4' draft pipe about 10" from the bottom. The top half of the pit is lined with a heavy steel box which the cooking grate sits on.

I have been playing with this thing for about 4 months. I have tried real oak wood, charcoal, and a mixture of both. I have also used a digital thermometer to see how temp varies.

The lid is made out of a fairly thick piece of aluminum that has a 4"x6" approx hole for draft also. I can have a fire built at 450 degrees and as soon as I put the lid on in about an hour its down to 200 degrees or lower.

No matter what I do it will not maintain heat. A hair dryer in the top of the 4' pipe is the only thing I can keep it going with. DO YOU THINK BIGGER PIPE WILL WORK? I have also tried putting a charcoal grate above the bottom pipe and it still wont draft.

Answer:-

The bottom draft is best "underneath" your fire and at worst level with your fire. From what you've described, your draft enters your pit 10" from the bottom and therefore above your fire?

The principle is that the hot air from your fire rises and as it exits at the top, it leaves a partial vacuum in the pit so fresh air gets pushed in the bottom draft. This fresh air is more oxygen to the fire so your fire goes faster and hotter which in turn pushes more heat out of the top. So the pit gets hotter and hotter.

It would appear that you're getting fresh air pushed in above the fire into the stream of hot air so this fresh air is going straight out of the pit and serving to cool the inside.

In addition, a larger diameter pipe (as you suggest) will have a positive effect. Have you tried a 4" soil pipe?