Just a little info on ducting and reduced airflow, from my perspective: Think of ducting as a cylinder, since that's what it essentially is. Now lets do a little calculation on the volume of air that needs to be moved through, we'll just say, 50 total feet of ducting. (Which I'm sure you don't have.) We'll also assume 4" ducting. V = (Pi)r2h, where r=2 inches(radius of 4 inches is 2 inches) and h=600 inches (50 feet is 600 inches) Volume of 50 feet of 4 inch ducting = 7539.82 Cubic Inches. Now we convert that to cubic feet: 4.36 Cubic feet. Use as much ducting as you want man, just try to steer clear of too many angles!
Does anyone have anything to add, in relation to reduced airflow from bends in the ducting? I can't really find formulas for that!