New forced air heater installed in the attic 3 years ago over one half of the house. In that half, the heat is great. Job was done by brother in law of a friend in evenings and on weekends as a side job. The guy's regular job is to install heating systems for a company. The other half of the house only has the master bedroom (the heater and master bedroom are separated by the 2+ story entrance to the house - so the attic has 2 accesses - over the master bedroom from a access panel in closet and over the rest of the house from access panel in the laundry room - there's crawl space over the entrance way if you really wanted to go from one side to the other. Ok, the problem. There was an old 14" galvanized steel return duct that was used in the old heating system as a return duct. This is now being used as a supply duct to the vents in the master suite. So 14" flex to the rigid, 20' run of the rigid steel (it's insulated) and again 14" flex to fabricated steel box running the length of the master suite, the "spine" which is 25' long. This spine has 3 ducts to the bedroom on one end and 2 to the bathroom on the other end. All of the air coming out of these are just warm and weak whereas on the other side of the house, the air is hot and forceful. I'm looking for things that I can do to make the air in the bedroom hotter and stronger - run flex for the entire run from heater to spine? use 10" for that new duct rather than 14"? get rid of the spine or reduce length of spine, putting only 1 vent rather than 3 for the bedroom? Any ideas appreciated.