I just thought of this earlier this morning, and wanted to run it by everyone here and see if it hasn't already been implemented in some fashion. Could you use the insulation space of a double-walled stove pipe for drawing external air in to feed the stove? Benefits include using external air to drive the fire (for obvious reasons), using the "wasted" heat of the chimney to pre-heat the incoming air for better combustion, keeping the chimney line even cooler, and not requiring a second hole in your house for an external air line to the stove. Cons include requiring a specially designed chimney cap (to make sure smoky air isn't pulled in), a specially designed stove (to be able to use external air coming through this passage), and specially designed stove pipe (since this channel would need to make complete runs through whatever bends exist in one's stack). Also the potential for more creosote buildup in the chimney with this cooling action? Anyway, does this sound like a good idea?