Reverse Smoker Build

[dog1234]

Hey guys,

I have a small revers smoker that I built years ago. I also have a lager bar-b-q pit that I have had for 15 years. I will be converting this pit to a reverse flow smoker. I have a few questions, how do I insulate the fire box. I saw fire brick can be used but how do I get them to stay on the top and not fall over from the sides. Also how do I apply Dave's calculations to an existing pit?

 

[tbern]

No help for you, but will bump this back towards the top.

 

[Hockeydudde]

When I've seen folks use fire brick, they place it only asking the bottom and up the sides of a round firebox. So the fire is sitting on the firebrick, but the top half is still exposed steel.
No personal experience, but I am interested in buying some and giving it a shot on my offset because I find my coals burn down too effectively. The wood goes straight from burning log to ash. I'm thinking the bricks will maintain some heat and block some airflow.

 

[chp]

I was planning to sleeve in another pipe into the firebox and let the dead air gap be the insulation. In my case, I have a 24” round FB and I found a 22” diameter pipe to sleeve. I can make a few spacers to center the pipe and try it. If it doesn’t behave correctly, it’s easy to remove.
As far as the calculator, you should be able to use the dimensions of your existing offset and base those on the exhaust plan (which I assume is what you want to use the calculator for?)

 

[seattlepitboss]

I went to a lot of trouble once to make a 2-layer insulated firebox. It was fun to figure out how to do it, but it added a lot of complexity. My goal was to make it more comfortable to stand near the firebox during a summer cook. The firebox worked exceptionally well but it still got quite warm near it. My conclusion was that insulating the firebox isn't worth the trouble.

If your goal is to make individual logs last longer, the only real way to do that is to use higher BTU wood. For example, you could go from hickory to walnut. If what you want is a big bed of hot coals, maybe you should start with a big fire damped down somewhat and let it go until it's all coals, then adjust air flow and temperature to normal and start cooking. Or use a secondary fire like the whole hog roasters and shovel in heaps of hot wood coals.

Thermodynamics tells us that heat will move from a hot place to a cold place. The question is how fast. If you perfectly insulated the firebox it seems to me you'd keep all the heat inside and thus burn up your logs even faster.

seattlepitboss

 

[dog1234]

I am considering insulating it for the main reason is to have the metal outer layer last longer. It seems to deteriate faster with the fire/heat.

 

[flatbroke]

I am considering insulating it for the main reason is to have the metal outer layer last longer. It seems to deteriate faster with the fire/heat.

I have seen pics where a couple guys weld flat stock to hold the sides and top brick in place. I have fire brick on the bottom of mine then set the grate on top. I haven’t bricked the inside top yet. Not sure I will. But has cross my mind. I think the sides are ok as the box is 2ft x2 ft.

 

[LanceR]

Hockeydudde , if you want more coals and you're using well seasoned wood you might try using half seasoned wood as that will result in more coals and smoke. Dry wood burns faster, hotter and cleaner so it won't give you as much smoke as semi-seasoned wood will and it is harder to run at low temperatures.

S seattlepitboss , the BTU content of wood is directly related to how dense and dry it is. Assuming the same moisture content, hickory, being quite a bit denser than walnut, generates about 30% more BTUs than walnut if the same cubic volume to wood is being burned.

Here's a table that could be useful: https://www.wood-heating-solutions.com/wood-species-btu-values/

 

[Hockeydudde]

Since this post I have indeed put fire brick in my fire box and am very happy. I can run a small hot coal bed that ignites the next split great.
I live in NM so partially seasoned wood is short lived here. Wood quickly stabilizes to single digit moisture content. I just measured some cut surfaces @ 0% lol.