Heat exchanger Butch, but I have seen smokers built the same way, and they work pretty well. If you really want to make it super efficient, you drill holes in both ends of the heat exchanger and run pipes through (welded or brazed so the smoke can't leak obviously) , and then put a blower box on one side... You can also run water through the pipes for hydronic systems too (ie in floor heat). A buddy made one that ran off corn, augered in from a hopper automatically, and heats water that is then piped to his house, heats the whole thing. Lol dude went all out, control valves and everything