Jeffrey Roberts

I have not, but I will check it out now. I'm surprised that your chimney is so small compared to the size of the drum. Does it get good enough draft to burn clean or is it smokey?

EDIT: Now that i'm watching this, I realize I have seen it but didn't put too much stock into it because I watched it when I was still building my 1 gallon TLUD and didn't think much of it applied. I will watch it again though since this is larger

My purpose is biochar also. Looking at plans for the 55 gallon drum stoves as you're talking about, as well as the 1 gallon stoves, the hole in the chimney is 50% of the total diameter of the burn chamber. On mine it's less than half of that. I think tomorrow I'm going to widen it and try another burn. I know for biochar production it should be a slower burn than if I were using it for cooking, but most of what I'm reading says there should be little to no smoke so I think mine's burning way too slowly.....

Okay - second run of the stove, and the results were worse with smaller fuel. I filled it with finger-diameter sticks from top to bottom, lit it up, and it burned great on one side (maybe too fast, even) but didn't burn evenly so the whole other side was basically untouched. The whole thing was REALLY smokey this time, but I have an observation:

It burns great without the crown part or chimney (so it's essentially a campfire in a garbage can), but as soon as I put the crown on (with or without the chimney) it would totally kill it. If I took the chimney off and lifted the crown part up an inch or so, it burst back into flames with no problem. To me, this indicates not enough air flow.... should I enlarge the hole in the top of the crown area? The whole top of the crown is about 15" wide, and the hole is approximately 3" in diameter. The other holes in the sides of the crown (10 of them) are 1/2" in diameter. Maybe more of them? Looking at the Toucan TLUD design, the crown is very open for its size and mine is not.

Thoughts?

What size of container are you burning in? My only previous experience was with the 1 gallon one and it smoked at the beginning, burned totally clear, and then my indicator that it was done was when it started smoking again towards the end. It's interesting to see different perspectives on this because there's a lot of variation!

I'll try that - I actually had it backwards from the way you suggested, but that makes sense about the gases. I was able to do all sorts of different sizes in my smaller TLUD (relatively speaking, of course, since it was only a gallon) at the same time without an issue though.

Here's something else I'm wondering about but I don't want to jump on any hunches yet because there's no going back once I drill more holes. If there's more ventilation in the crown or chimney, it will ignite the gases (although any ignition should light up all of them, right?). More burning of gases = more heat = more draw. Does that sound right? Or if this problem persists, should I go with more ventilation in the bottom? It's propped up on bricks, so plenty of ways for air to get in...

I've been using the Toucan TLUD (1 gallon) design for awhile now and wanted something bigger, so I started from scratch using a 20 gallon galvanized trash can as my burner. For the "crown" section I used an inverted 3 gallon galvanized livestock water dish with a 3" hole in the center and an 8"x2' chimney. There are about 50 or so half-inch holes in the bottom of the garbage can, and a dozen or so in the crown.

I did two burns today and the first burned out after the top 6" charred, and the second one burned REAL SLOW, but eventually did get to the bottom, although it wasn't an even burn and I still had some raw wood left. I'm chalking that up to poor choice in fuel. Not all of it was the same diameter...it ranged from chunks of bark to 4" or so diameter by 2' length logs. In general, I got little ash and more char from the second burn than I've gotten from all of my runs with the 1 gallon TLUD combined, but it was a SLOW burn and it was VERY smokey. Several times I thought it was going to go out. I never did get the "rocket effect" of flames coming out of the chimney like I did with the small version.

I know smoke can indicate too much air or not enough air, and I'm inclined to believe that this is not enough air. With the lack of large flame, slow burn time, and smoke, does that sound right? If so, would it make more sense to put more ventilation holes in the bottom of the trash can, in the crown area, or both?

I've done some reading around on this site and others but haven't found a satisfactory answer to my question. I'd eventually like to make a permanent RMS to complement my back yard fire pit because we do a fair amount of cooking outside all year long, but I want to get a feel for design first so I'm going to build a few of the tin can models to see what I like or don't like. My question is related to maximizing efficiency and minimizing smoke.

It seems to me that the diameters of the horizontal and vertical pieces would affect air flow, as well as chimney height. What I'm wondering is this...to maximize draft, it seems that the chimney should be higher, right? If so, what's the commonly accepted practice in terms of the diameter of the vertical and horizontal pieces (again, using the basic coffee/soup can idea). Should they be the same diameter? Would it draw better if one or the other was narrower? Fluids (gases) travel faster in smaller diameter pipes, but the trade off of narrowing pipe diameter would be either having a smaller area for the flame to contact a pot or pan on top, or else having even less space to put fuel.

What are your thoughts?