I have seen primitive technology and I will say his natural draft furnace is very impressive. My only concern about that furnace type is that the air flow is not as penetrating and regulated so you can burn your iron. He was also using low grade bog iron ore (seems to be all he could find) and I have some pretty high quality ores in my area which works to my advantage. I actually got into blacksmithing when I was in middle school thanks to Runescape. I started heating pieces of rebar up in a campfire and smacking them on rocks with a hammer.