wayne wrote:
So you don't have several return ducts in different rooms? I have 3 in
my house?

Built in 1982. 1200 sq ft.

Return air comes thru ONE single point source, a plenum of plywood and
timber underneath the furnace (up flow model).

Extremely common building practice in the late 70s and early 80s in most
parts of the USA that use forced air heating and cooling.

Houses in the 90s started the return duct per room idea ( at least for
rooms with size)

Supply ducts to laundry room, master bedroom, master dressing area and
master bath are under 6 feet long. Kitchen and living room ducts are
under 10 feet long