Without getting too technical I have a simple question. My system was recently installed. Lots of air movement, 10 ceiling diffusers and two air returns. My living room however is a bigger room with a door and two large windows. It doesn't get as warm as i would like. I looked at the plenum and there isn't anymore space for another takeoff. I would like to add another ceiling diffuser in that room but I cant really see any way. It's all 8" flex duct in the attic, flex rests right on the attic floor in fairly short runs. Someone suggested using a "Y" and adding another run off the flex. Is this ever done? does it cut airflow down much? the new piece would be about 8 feet. Any suggestions would be useful and appreciated.