I would like to put some heat in my basement. Since my house is zoned I thought I would run 2 lines. I would like to tap a 6 inch off my 1st floor duct and a 6 inch off my 2nd floor duct. Does this sound okay and what might I need for cold air returns?
I would not tap off of a existing duct, since that would cause airflow in those rooms to be less. As for the cold air return, that is a debate that both sides say yeah or nae on. I did not do it, because of the fact that I have a unfinished basement, and have enough cold air return on the main floor to take care of the whole house (2 returns 2'x3' in size).