The system y'all are referring to is called a "snow melt" system and it's traditionally hydronic or steam driven so it's usually work covered by the "wet" side of the HVACR community, that is, steam/pipe fitters and or plumbers. After visiting Wheaton Labs this past October for the RMH Jamboree it came to me that a dry snowmelt system would be an awesome thing to test. I live in a small town that calls itself a city so the city government can have more control over how the community looks; they would insist upon permits and fees for a permanent roof of any kind over the driveway. They would not, however, even notice if I dug up my driveway, installed piping and covered it back up. While grade would have to be a consideration for melt run off, I think a driveway with a pronounced grade would be a better fit for a RMH snow melt system than a flat or slightly graded driveway. Tossing off the idea, I'd build the firebox at the bottom of the drive, break off a 10" round feed to a true manifold that fed a number of square duct runs up the drive, opened up into a bell and exhausted from there. I'd make sure the ducting had the same or slightly higher combined cross sectional area as the system itself.