Meet Thomas the TLUD - top-lit up-draught stove. This one is made from a 5L paint tin pyrolysis chamber inside, an old wastebin on the outside, and a 3L paint tin chimney/combustion chamber. And it goes like the clappers! 4L of wood chips gives a beautiful 20min burn that provides stacks of heat and generates about a litre of charcoal. I'll run some more tests and get some proper figures on this.
Suffice it to say that the TLUD is the way of the future. Forget braziers and patio heaters - this is hot hot heat from fully renewable sources.