This was my first very crude furnace. Basically just an oil-drum full of fuel and a fan (heater fan from a Toyota car). The first part of the flue was a 10 foot long water-jacket heat-exchanger that I made myself. Interesting but not very practical. (Click on picture to enlarge)
A similar furnace but this time with a collection of oil-drums to store the hot water. I was most interested in getting the flow of water right before I built a more serious heat-store, I knew the furnace was not up to the job and the heat store was going to need lots of insulation before there would be any realistic chance of storing heat. (Click on picture to enlarge)
Here is the new improved furnace with its own framework and compact cast-iron heat-exchanger. Too many problems with this creation to mention, it now sits at the back of my shed! (Click on picture to enlarge)
This furnace was constructed out of an old digger bucket. Although the furnace worked well, the stack of cast-iron heat-exchangers easily became clogged with tar, and our old friend 'automation' was clearly going to be a big problem again. After this, I abandoned furnaces as not really being what I was looking for. (Click on picture to enlarge)