Appropriately, I learned about rocket stoves from a priest of Hephaestus.
Rocket stoves do a few things differently than other stoves. Most notable is that they direct airflow from the first spark, using that airflow to turn a small fire into a small blast furnace. Only a small amount of the fuel (say, three sticks the size of highlighter pens) is available to burn at any time — just the very tip — but the blast furnace effect makes that fire very, very hot. The result is that you get huge amounts of heat from a very small flame, very little fuel converting to make that heat, and so very little waste floating away in gas form.
The fuel economy was pretty neat. The use of the heat was pretty neat. The use of the waste heat, the heat that goes up the chimney (or heats the chimney, and thereby the outside air) to heat, say, the floor, was really neat. The nicest use of a rocket stove is to build a cob house and direct waste gas pipes through the cob, heating the floors or furniture. We used four cords of wood this winter. With a rocket stove we would have used 2/3 of a cord, and been more comfortable.
Too good to be true. I couldn’t believe it. So, when I got home from Norwescon, I made one in miniature.
On the way home yesterday, we stopped at the grocery store so I could buy the #10 can of my choice. I selected pineapple chunks. When we got home, I used a pair of utility shears to
cut the ends off of a “tall boy” beer can, then a hole in the top of the #10 can, just smaller than the beer can.
I dumped the pineapple out at this point. Just want to be clear; I feel the pineapple would have skewed the results. Shannon pointed out that I would be happier if I took the label off, as well.
Taking my modified cans down to the shop, I poked around until I found a 6 foot length of drain pipe, then made a second hole in the #10 can to accommodate it.
Insert the beer can to about an inch above bottom. Insert the drain pipe just barely. I was lucky; the whole thing balanced.
I stuffed a paper towel into the bottom of the can and used a piece of kindling to shove it to one side. Then I lit the kindling and used it to light the paper towel.
Five seconds later I could hear the roaring of air as the paper towel went into blast mode. I dropped three pieces of kindling into the hopper.
Less than five minutes later I had turned the #10 can bright red, and shown that Shannon was right; I should have taken off the label. I was excited, and forgot.
Less half an hour, and the 20x20x14 shop was easily room temperature, while the outside temp was around 55. I used a double handful of small sticks from around the woodpile. It was an hour after I had started modifying the pineapple can.
I am stunned.
I don’t see fire in a bucket. I see heating for the house for $150 a year. I see a cob house that I can afford to build without spending the rest of my life paying for it. I see freedom.