I have a room in my colonial that is always the coldest in winter and warmest in summer. It is the furthest from the furnace so it is to be somewhat expected. I did not want to go another winter with an electric baseboard heater in the room again so I thought I would try a booster fan... it has boosted the the air flow but just wasn't enough. Then one night the door was left open and the room was actually warmer than it usually was so I immediately check the cold air return to discover very weak if any suction. I tied a washer to a string and checked to make sure there was a hole in the baseboard and there was, I then went and checked the basement to try to find the cold air run but was unable to locate it. I even hung a radio in front of the grill to try to hear it in the basement but was not successful, I have a finished basement with the ducts wrapped in drywall, I do have limited access since half the basement is drop ceiling. I searched for cold air return booster fans but have not found any.....Any suggestions would be greatly appreciated! The home is 10 years old with a +90.