The size of the pot should be 5 -8" in diameter, that would give enough room to anneal a butt plate. The depth of the pot is very important. Four inches is a good depth. Forced air fires will oxidize metals and we want a fire deep enough to consume as much oxogen as possible. The metal should be kept near the top of the fire and covered with a little charcoal. The deeper into the fire, the more oxogen. It is surprising how little air is needed to get a hot fire, note the ragged fit around the fan.