What not to do for your J tube

We built our first RMH last winter and you could say we cut a few corners as winter was fast approaching in our newly purchased house. Meaning cash was tight so cheap was the name of the game. My beloved was a welder at the time and received this beautiful length of mild steel tubing. He cut it up and welded it together to form a metal J tube. We were told not to do this but did it anyways cause fire brick is expensive and this was easy. It went out a month before the end of winter last season. Heres some pictures for good examples of what not to build your J tube from. But it did last two years! Giving us plenty of time to source the time money and free fire brick from a a old chimney to build it up right and safely this year. We knew she was going out this last season so we kept a strict eye on her to make sure there was no real fire risk. I think they are surprisingly safe from our experience. The biggest threat was the rate that it can fill a place with smoke if it gets choked out or there's to big of holes in the system.

Just a note that we had pulled her apart after the first season to do some modifications and replace the tube but at that point there was very little scaling along the riser where the rock blanket hugged it. And there was no ash or creosote build up. So we decided to see how long it would last. Partially cause we are lazy but also for science!

Excellent post, thank you for sharing!
Sometimes you need to make do with what is available.
Two seasons is pretty good for a metal J-tube.
This season, with firebricks for your core, I think you will be very happy!

I think you are right we are also expanding the burn tube to a 6 inch system, 4 inches kind of sucked for fitting wood in it.

Just be sure not to make the burn tunnel roof more than 10-12". Too long will work, but it will fill the system with ash before spring.

I bet thats what was wrong with the metal one, Id have to go check but I think that one was closer to the 12 inch mark. I just measured the new brick one and its at the 9 inch mark thankfully. I'm not the numbers person. I just play in the mud and put it together from the pattern lol.

Hey Sam, looking at your photo, the feed tube appears to be rather shallow.
Normal depth for a J-Tube, feed tube is 16"  
Wood is commonly cut to 16"; this keeps your wood entirely contained, with no chance of a piece tipping over onto your floor.

I just took the tape measure to it and yeah. I need to add another layer! Thankyou for noticing before I put her back together. Beloved then measured the riser to find it is also a layer short. I must have missed a step in my instructions while building it. I guess measure twice, tear the RMH apart only once.

Thank you for sharing Sam. Kind of expected results but good to have a visual and document failures as well as success.

Tom, can you explain why a longer burn tunnel leads to more ash?

I don't have a proven technical reason, other than guessing an incomplete burn.
One year, I did a summer rebuild on my 8" J-Tube, with a piped system.
I extended the burn tunnel to have a 15" roof. (If 10" was good 15" must be better, right???)
For the first 3 months, it seemed to work great!
During the 4th month, I noticed that it seemed to be not as rockety, by the fifth month, it was stalling and smoking back.
This 5th month happened to be February in northern Montana.
The J-Tube was in my wife's uninsulated artist studio...
I was lucky enough to catch a sunny 35F day to open the stove up.
I found my transition area full of ash AND my 8" pipe was reduced to apx 1.5" at the top of the pipe...
That ash made it all the way through the horizontal pipe to the vertical turn to go up the chimney.

GOOD GRIEF!   I was frantic.
This was where I learned just how fast and easy a J-Tube rebuild/repair can be.
I started at 8 a.m., and I was relighting at 1 pm!  
Core rebuilt to an 11" burn tunnel roof, transition area, and pipes vacuumed and blown out.
Starting to cool off in the room but quickly warmed back up as soon as the dragon started roaring!