The back room of my house is quite warm in the summer. The room is on the north side of the house (Alabama, USA), so the outside walls don't get direct sun exposure. The attic insulation is a little on the low side, but comparable to the rest of the house. The HVAC air handler is on the opposite end of the house. There are two air returns, one near the air handler and the other just a few feet from the room in question. The nearby return has a 40 foot run to the air handler. The air handler feeds a trunk line that runs about 35 feet. Near the end of the trunk are two 6 inch flexible ducts that go the remaining distance to the room (25-30 feet).
I have considered a few alternatives to resolving the problem.
1) replace the 6 inch ducts with larger ducts.
2) add another duct line and duct.
3) install a duct fan to boost air flow.
While I'm completely capable of doing the electrical part to code (and safely), I'd prefer either of the other two options. Which of these options is best? Or is there another better option?