I am a commercial plumber and have been for 15 years. I was a commercial pipefitter for about 5 of those years and really, truly understand the heating and cooling ends of HVAC. Its ductwork I dont understand. Im not looking for a handout or anything like that. Im a tradesman as much as most of you are. Here is my problem... I just bought a cape cod that is 2 years old, the cape(upstairs) wasnt finished. I am finishing it now and have absolutely no clue on what size duct to run up to the cape part of the house. I have been looking for 2 weeks on this darn internet trying to find "the answer". If someone could give me a website....any clue as how to size this damn ductline I'd appreciate it.