When I come under my house (crawlspace throughout the floorplan) , I am blocked by duct work everywhere. I know that I can remove any segment to get through but I wonder why ? You see, the floor joist has rows and rows of clearance that I can tuck the ducts up neatly and out of sight or that I can move the duct work above the ceiling in the attic space. My gas furnace pulls in air from the ceiling airspace and push air under the entire house through ductwork throughout the crawlspace, so I guess it is better to keep the same configuration as before . The floor register holes are already there orignally. I am cost conscious so I am asking for anyone's advice about how to realign the entire ductwork with most sections tucked between floor joists which is 8 or 10" . I can draw a diagram of how the floor joists are arranged but I dont think it is necessary. My main problem is that the floor joists may cross the path of the original duct branches. I have about 8 or 9 registers mostly floor and a couple of them off the wall a foot or so above the floor like for bathrooms. It looks like I have to make some necessary detours in order to tuck up as much sections as possible following the joist layout. Some sections will still have to be placed under joist in "J" coupling in order to get to the floor joists. All of the floor joists are close to the perimeter of my house. I feel I can move some of the floor registers closer to the central furnace to save on the traveling distance of the heated air toward the floor registers. Some of the duct branches are ridiculously lengthy like 80 or 90 feet between the furnace blower and the floor registers because the furnace is placed at the end of the house instead of center of the house. My goal is to make all registers no longer than 50 foot or so so to cut down on the heat loss. I might eliminate the furthest registers outright so to save on heat loss. Some of the rooms especially bedrooms can be shared with same register on the double side off the wall and the unwanted far-off floor registers capped off. I wonder about regulations and safety . I figure if I use the same number of registers as originally, it should not be a problem. I think I can eliminate a couple branches since my new furnace and blower are more energy efficient as the blower is less powerful than the original one made back in 1970. The original one blew more air than the newer one. I want my crawlspace all cleared of the blocking ductwork . If I tucked most fo the duct segments between floor joists, I can nail 1/4" plywood covering under the joists after stuffing insulation around the duct sections. Am I brilliant or what? Has anyone else done that already ? Eh?