This is a supplemental MIDGE building instruction, which includes some small modest modifications that I have made to Chris’s original elegant design. Note, that I have not include information on the sizes or numbers of the various holes that need to be made in the cans. Those can be found in Chris’s original MIDGE instructions (see “The Complete MIDGE”). There is very little difference between this and the original. It only extends the Burner Cap, for improved insulation, uses a variety of interchangeable Burner sizes, and has a can as a Burner Stand. Except for the increased insulation, the function is straight original MIDGE. I have not yet been able to improve on it.
-This is 4¼” dia x about 7″ tall.
-A standard 46oz juice can or equivalent. It gets holes punched in it sides around the base.
-This can be a 15oz vegetable can, or a soup can, or even a spaghetti sauce can. There is wide latitude in size for this one.
-It gets the bottom punched full of little holes, so air rises through. It could even have the bottom cut out, and replaced with a big screen, like ¼” hardware cloth. Small holes get punched all around the side, at the top.
This can needs to be just slightly smaller in diameter, than the cowl, so that it will fit down inside of the cowl. A large tuna can (12oz) or a large refried bean can, or a variety of other cans will fit there. I like a tall can, because it adds an additional layer of air, and another shiny metal surface for radiant insulation. That will make the fire hotter, and keep the inside of the cowl shiny longer, for a cooler exterior surface, The burner cap, gets a hole in the center of the bottom. It can be about 3″ dia, or smaller. I have not experimented with a lot of sizes.
A quick note on insulation:
This stove works on a few different insulation principles that most of us are not used to thinking about. It uses no standard insulation materials. Instead it has layers of shiny metal, that have a low value of “emissivity” which is a fancy word for saying that it reflects the heat back. That reduces its radiant heat loss, and keeps the fire chamber hot. The air spaces do the rest, but these air spaces do not just slow the heat from getting out, like most air space insulate. All these air spaces are preheaters for the combustion air, so they also carry the escaping heat, right back into the stove, to make the fire hot enough for very good combustion and gasification, even though there is no conventional insulation used. When the stove is fresh and shiny, you may even be able to pick it up with your bare finger for a few minutes into the burn (this would be your responsibility, not mine). Once the surfaces get dirty, as happens very quickly to the burner, the radiant insulation effect is greatly reduced. However, the other cans stay shiny for a while, and are easy to replace, so you can keep the insulation value high if you care to. The Cowl is kept cool by the fresh air being drawn in. Once the fire goes out, the temp of the Cowl may actually get hotter.
That is the three main cans. There is another can which I use:
A standard 6oz tuna can, with a bunch of holes in the sides and bottom, as a stand (bottom up) for the burner to set on top off.
1)The cowl sets, open end up. 2)The Burner Stand get dropped, (open end down) into the cowl 3) The burner sets on the stand (open end up)
4) The burner cap is dropped down (open end down) over the burner, inside of the cowl.
To operate it.
1) Fill the burner roughly half full of fuel. As you may have read, the fuel can be sticks, wood pellets, or even shredded junk mail. Many choices, but start with these first. It needs to allow some air flow, but need not be loose. 2) With the burner cap in place, light the top of the fuel. It may need some help. I use a little crumbled candle wax. 3) You will get a little smoke at first, until the gasification starts. It may take two minutes. After that you will see some blue flame that looks like it is coming from the secondary air vents around the perimeter. That is your WoodGas, burning as it mixes with the fresh combustion air. You can look down into the chamber, through the flow of the WoodGas, to see the wood
being cooked, in the oxygen deprived environment.