Simon in New Zealand, was the first person to build one of these heaters, and also send of photos of it during construction. He is a very acomplished "tinkerer", with a background in the Mechanical trades, the standard of his work really opened my eyes, because at this time my heater had been in service for many years and still displayed it's rather "agricultural" heritage, whereas his heater was a work of art in comparison.
I think it would be fair to say, that at first he was perhaps justifiably suspicious of my story as to how easy it was to get old sump oil to burn with no smoke or smell. For those of you who have ever put it on an open fire you will understand, it has plenty of heat, but the smoke is black and the smell is obnoxious to say the least, soooo,.... I asked him to try a scaled down temporary setup and give it a try.
The photo at left shows what he did. An empty tin, a piece of galvanised iron on top to support an old cylinder liner and a couple of lengths of flue pipe . I think that i can say that the results surprised him, and as you can see, it is poking out quite a bit of heat. :-)
What is shown here is about as basic as you can get, and would suffice as a heater, so long as precautions were taken to replace the light material as it burnt out and some form of safety barrier was put in place to protect inquisitive fingers and other flammable matter. There is no absolute necessity to have a large firebox as I have, except to give more area for heat radiation to the surrounding space.