Trouble with Heat Transfer on my DIY Smoker

[scrappyjeff]

Hello all,
Looking for a little help here! I helped a buddy build a very crude direct smoker a few years ago but other than that I have little to no experience with smoking so naturally I built a complicated offset smoker. I had the time and the materials were cheap so I went for it in hopes of brisket and ribs. The smoker is in the photos below. The fire box is 12x12x8”and the cook shed is 15x16x34”. I seem to have decent airflow from the firebox through the cook shed and out the the vent up top. I can transfer smoke well but heat is another story. I can’t get it above 180. I’ve calibrated/tested my thermometer. I’ve got a nice bed of hot coals going in the firebox but I don’t know where the heat is going. My initial thoughts on possible issues:

1- I put the transfer pipe through the second layer of bricks, not the top layer. Is the heat rising above my pipe and getting transferred into the concrete roof of the firebox?
2- Is it the 6 inch long 1 1/2” galvanized transfer pipe? Too narrow of a diameter? Too thick and absorbing heat?
3- Firebox is just too small?

I would appreciate the knowledge from anyone with experience as I don’t want to make any modifications that might be a bust. Thanks in advance!

 

[JLeonard]

It a great looking design! I like it. daveomak might can help you out. He's the resident guru.
Jim

 

[Brokenhandle]

Your 1 1/2" transfer pipe is too small and it should have been at the top of fire box. From the discoloring above and to the right of firebox door I'm betting that's where all your heat is escaping.

Ryan

 

[scrappyjeff]

Your 1 1/2" transfer pipe is too small and it should have been at the top of fire box. From the discoloring above and to the right of firebox door I'm betting that's where all your heat is escaping.

Ryan

Thank you, I’m not scared to drill into my brick to solve the issue. But it will definitely be easier to drill smaller holes. Would multiple 1” or 1 1/2” pipes do the same trick as one big one?

 

[mike243]

You will poison somebody with the galvanized if your not lucky look it up please , we want you enjoying bbq for a long time

 

[scrappyjeff]

It a great looking design! I like it. daveomak might can help you out. He's the resident guru.
Jim

Thanks you. I was s

You will poison somebody with the galvanized if your not lucky look it up please , we want you enjoying bbq for a long time

Thank you. Luckily, since the smoker doesn’t work no meat was cooked with smoke through the pipe. Any suggestions on a safe alternative?

 

[unclebubbas bbq]

Looks great but there are a few issues as mentioned. One get rid of the galvanized pipe, someone will get sick from it if not kill you.
2nd the opening between the fire box and the cook chamber needs to be much larger, my guess would be 6" in diameter. Once you do that you will see a dramatic increase in heat. How big is your exhaust? Lastly you may need a heat shield to protect your meat from burning. It's going to be all trial and error

 

[scrappyjeff]

Looks great but there are a few issues as mentioned. One get rid of the galvanized pipe, someone will get sick from it if not kill you.
2nd the opening between the fire box and the cook chamber needs to be much larger, my guess would be 6" in diameter. Once you do that you will see a dramatic increase in heat. How big is your exhaust? Lastly you may need a heat shield to protect your meat from burning. It's going to be all trial and error

Gotcha! Galvy has been removed. Exhaust is a 3” diameter. Thank you for your input.

 

[daveomak]

FB to CC pipe should be 4-6" to get the heat into the Cook Chamber like Uncle Bubba noted...
And near the top of the Fire Box...

 

[Winterrider]

I see good results in your near future S scrappyjeff . I know nothing about designing one but these guys know there stuff. Great people on here, and Welcome from ND.

 

[thirdeye]

I agree with everyone that you need to improve your draft, both intake and vent. And also change out the galvanized pipe. Your firebox ash tray is nice, but I'm thinking a piece of expanded metal maybe 1.5" off the bottom would let air come in from underneath, and let ash fall into the bottom. Ash free coals are happy coals. This might be better for burning small chunks of flavor wood too, you don't want them to choke out or smolder.

 

[bill1]

The short answer to "where is the heat going?" is: "Into the brick and concrete."
Most offset smokers have at least one wall in common between the firebox and cook chamber. This has zero.

Most all the heat in the firebox is intercepted by brick or concrete (B or C). The area of the pipe is a very small fraction of the wall area of the firebox, so as many have said, it needs to be bigger.

B&C are good high-temp materials but they're not very good as thermal insulators. Air is better. It would be great if you could build a small 5-sided steel box that fits INSIDE the B&C firebox. The steel on your present door can be the 6th side. The walls should be such that there's a ~.5" gap to any BorC. It can sit on 3 large nuts as feet. Yes, the outside of that steel box will get hot, but the air gap will transfer a minimal amount of heat to the B&C; right now almost all the heat is going there. The exhaust pipe then is the predominant path for heat to leave the firebox and it's going where you want it. Ideally that pipe is not in intimate contact with any B&C or free-moving air, otherwise you'll lose a lot of heat that way. A good way to do this is to put a pipe in a pipe, with enclosed air the insulator between the two. Of course you need something to keep gravity from making them fall together to their lowest point, but just a few marbles or ball bearings (whose contact area is small) will do the trick.

 

[scrappyjeff]

The short answer to "where is the heat going?" is: "Into the brick and concrete."
Most offset smokers have at least one wall in common between the firebox and cook chamber. This has zero.

Most all the heat in the firebox is intercepted by brick or concrete (B or C). The area of the pipe is a very small fraction of the wall area of the firebox, so as many have said, it needs to be bigger.

B&C are good high-temp materials but they're not very good as thermal insulators. Air is better. It would be great if you could build a small 5-sided steel box that fits INSIDE the B&C firebox. The steel on your present door can be the 6th side. The walls should be such that there's a ~.5" gap to any BorC. It can sit on 3 large nuts as feet. Yes, the outside of that steel box will get hot, but the air gap will transfer a minimal amount of heat to the B&C; right now almost all the heat is going there. The exhaust pipe then is the predominant path for heat to leave the firebox and it's going where you want it. Ideally that pipe is not in intimate contact with any B&C or free-moving air, otherwise you'll lose a lot of heat that way. A good way to do this is to put a pipe in a pipe, with enclosed air the insulator between the two. Of course you need something to keep gravity from making them fall together to their lowest point, but just a few marbles or ball bearings (whose contact area is small) will do the trick.

I appreciate the your time and knowledge. Step one of the redesign will be blasting some bigger holes in the top layer of bricks for more airflow. Then I will try to make the 5 sided metal box.

 

[scrappyjeff]

I agree with everyone that you need to improve your draft, both intake and vent. And also change out the galvanized pipe. Your firebox ash tray is nice, but I'm thinking a piece of expanded metal maybe 1.5" off the bottom would let air come in from underneath, and let ash fall into the bottom. Ash free coals are happy coals. This might be better for burning small chunks of flavor wood too, you don't want them to choke out or smolder.

Fixing the ash tray is a lot less daunting than the rest of the redesign. I’ll add that to the punch list! Thanks.