My pit needs help. Almost there.

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Qbert60

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Hey folks. I have the following issues that I am hoping the people here can help address.

The PIT:

Dimensions - 48" L x 24" H x 36" W. The cooker has 6 sides to it. I know weird right? It was a pit that was on a trailer that LOWES had out parked out in front of the store. I wouldn't normally have bought, BUT I was able to knock down the price significantly. It's 1/8" steel plate and it leaks like bad plumbing. It has a similar shaped offset firebox that is connected to the chamber via square tube. Very inefficient. Google Carry-on BBQ Trailer and you can see. Don't judge me.

The IDEAS:

New firebox, a lowered smoke stack, and a 2nd shelf in the chamber.

What I've DONE:

Fab shop built a 24" x 24" x 24" with 2 " insulation firebox. I modeled it using the BBQ Calculator. Full size door. About a 5" L x 2" W vent. (I know, not close to be long enough.) Opening to the chamber is is 18"W x 6"H. Honestly looks Bad A$$.

Also lowered the smoke stack to grate level. According to the BBQ Calculator, I needed 1, 6" diameter pipe about 36" high. He didn't have 6" pipe, so he made 2, 3.5" stacks and offset them, one on top of the other. THe bottom one is 36" high and the other one is about 25" high

Problems:

I don't think I am getting enough draft. The pit only got up to about 150*. I know that the vent on the firebox isn't close to being large enough, but I look at the Jambo boxes (with out the boiler door) and I don't see a vent to begin with. Now, the box doesn't have a fire grate in it yet. I used a small charcoal basket I made for my offset Char-griller. I lit some lump, let it get ashy, and through some hickory splits in it. Maybe not enough? I have to hold the firebox door open to keep the fire lit. Any idea's how high the grate (I am building one) should be in relation to the openning to the cook chamber?

Please help me?
 
It sounds like you have 2 problems... The major of the 2 IMHO is the exhaust. I don't believe you are getting enough. might need to go bigger on pipe size or longer. You don't always need vents if you have a good draw. Having said that, You do need bigger vents or more of them.
 
put a fan at the vent and see if piping more air in changes things, or add more wood for more heat?
 
I wasn't able to find any pictures of your pit with a google.
A few pictures would really help.
There are some really knowledgeable people on this site.:-D
jon
 

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I used a small charcoal basket I made for my offset Char-griller. I lit some lump, let it get ashy, and through some hickory splits in it. Maybe not enough? I have to hold the firebox door open to keep the fire lit.
Click to expand...

How large of a fire did you make? Did you get the pit up to temp?
It takes quite a bit of charcoal and wood to get a pit that size to temp and burning cleanly. I usually plan on an hour on my stick burner.
You can test the intake vent sizing by increasing air flow (just open the door til you get a fire going and the pit to temp). Once you are at temp, open the vent and see how you can maintain the temp or if it chokes the fire out.
Does smoke roll out of both exhaust pipes? I haven't seen exhausts stacked like that before.
If you don't have a 6 inch pipe, could you make a 6 sided pipe to match the smokers other profiles? From your calculations it sounds like you will need more exhaust.

If you have about 6 inch space under fire grate you will leave yourself room for ash build up and still have good air flow feeding your fire. A pan for ashes is nice for clean up also.
jon
 
your intakes should add up in volume to your exhaust.. this helps it draft a little better.. you may look at adding some intakes below the fire grate on the sides of the fire box.. also how high up off the bottom of the fire box is the fire grate? that could be the problem also.. you want the fire grate to be above the top of your intakes..
 
If the pit calculator told you to use 6" pipe that's about 28 sq. inches. Your two 3.5" pipes are around 18 sq. inches. You need a bit more than 1 more 3.5" pipe 36" long. Might go with 4" to offset the 25" long one.
 
It sounds like to me if the pit is only getting to 150 degrees . Then your draft is a issue. Which means your air intake at fire box is too small and exhaust stack is to small. Sounds like you are starving your fire of air and fire is not burning clean. Also in pics it looks as if one stack is higher than other. In this situation I believe that both stacks should be at the lower position . Heat rises and the stack at top may be exhausting all the heat in main chamber .
 
The base of your fire grate should be 1" above the top of the intake. Sounds to me like you have a flow problem get the fire raised if that doesn't correct the problem you will have to increase the size of the intake openings. Also your fire box opening is located to high it should be below grate level. That lets the heat rise to the top of the pit to soon. The way it is now I would bet it is cold in the middle and hot on both ends. the heat should enter below the grated and rise up through it.
 
So here is my problem, I think. When I used the BBQ calculator, I was using the outside the dimensions instead of the interior dimensions. Is that a problem?
 
Bludawg said:
The base of your fire grate should be 1" above the top of the intake. Sounds to me like you have a flow problem get the fire raised if that doesn't correct the problem you will have to increase the size of the intake openings. Also your fire box opening is located to high it should be below grate level. That lets the heat rise to the top of the pit to soon. The way it is now I would bet it is cold in the middle and hot on both ends. the heat should enter below the grated and rise up through it.
Click to expand...

I get what you are saying, but how is it that the Jambo's opening is at grate level?
 
I've never seen one, I just know what works on what I have and what i have built.
 
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