I'm finishing my basement, and I'd like to screw my drywall ceilings directly to the floor joists from the 1st floor. Is there a type of ductwork that is considered "low profile"? Something that could fit between the joists?
What size are your joists? Keep in mind, changing the ducts, can change the aspect of how efficient your unit is. Change the size of the duct work, you can open up a huge can of worms. With that, you could find that the upstairs no longer heats or cools as it should, or could cause short cycling.