First post...Great site!
As many others have experienced, I have a hot upstairs in a 2-story house. New construction circa 2002. Out of the 4 bedrooms, the only one that is cool has suction from the return register located at the top of the wall in the room. This room is located in the center of the house directly above the furnace and uses the wall cavity between the studs as the return duct. Plenty of suction through the register in this room. The other 3 rooms that are significantly warmer use 8 or 9 inch insulated flex duct that is connected to a large wall cavity next to the furnace. The flex duct runs from that connection through the attic and down to the rooms through a ceiling register. There is probably 100 feet total of flex duct including a junction box where the single duct branches out to 3. There is not only no suction in the ceiling registers, but there is minimal at the start of the flex duct at the wall cavity. I know the cavity is not blocked because I tossed some rope through the opening and it came out at the furnace connection.
I just got off the phone with the company that installed the furnace and the service tech stated that there shouldn't be any air-flow through the return ducts and they are there to release the pressure in the room. His exact words were " you should be able to hold a candle next to the return registers and not have it move much." I found this statement a bit odd as other threads I have read state that the return registers should be able to hold a piece of paper when the fan is on.
I was going to have the company come out at my expense ( out of warranty) but the explanation from the service tech seemed off. I am no expert, but shouldn't the return ducts all pull air back to the furnace?
I have a 3 Ton Carrier System. House is around 2000 square feet. I even went so far as to disconnect a branch of the return ducting for the downstairs and blocked it off as to create more air-flow for the upstairs. Went back in the attic where the flex-duct started and still nothing.
Thanks in advance for your responses.