Interesting. Some of the ductwork was installed 10 years ago, some were here since 1887 (floor joists with tin nailed to them to make a duct). The existing furnace is undersized for the size of the house, 115k net BTU's isn't enough for 3,000 square feet with 10' ceilings, 8 doors, and too many to count six foot tall single pane windows. I'm thinking they set it up the old way to get away with an undersized furnace? Has anyone done a study or any testing to determine the difference between methods, maybe to see what uses less fuel or makes the house more comfortable? It's not hard to switch the ductwork, but switching back isn't going to be easy.