It's about my 40-yr old 2-storey house in midwest Canada. After taking off
part of basement ceiling, I found something weird with a heating duct. It
runs up from basement to main floor along an exterior wall (built into the
fiberglass insulation), and maybe further up to the second floor, and to
attic??? I'm sure no heating vent in the house uses this duct. I just can't
figure out where is goes. It sends hot air to attic to do heating? possible
for an old house?

please help solve the mystery. Thanks.