I am having a problem that i am sure many have and that is getting enough air/heat to my down stairs. The main trunk line coming from the furnace goes about 6 feet and then drops within the wall cavities and splits(I assume)to the
down stairs rooms. However, all of the rooms down stairs
except for the den (30X20) gets pretty good flow coming from the registers. When i place my hands over, I barely
feel anything. Is there something that can be done, short of having half my drywall or flooring torn apart?

Thanks