Well the new furnace has been designed and thought through intensely and the final verdict has been passed. PLEASE READ THIS THREAD which contains the start of the idea and changes up to the final product that will be made if you do not understand the bottom illistrations.
Click on pic for a bigger one.
Blue - Air route through heat exchanger
Green - Exhaust gas route through heat exchanger
I will be using a used electric hot water unit for the shell and the internal molds will be made in separate pieces that will fit together using a 1 inch dowel that will be centered and hold everything in place while the refractory is poured and rammed. Pictures of the actual pieces and building will follow soon.