I have a gas furnace/air-conditioner combo unit that vents to the
outside through a grille on my exterior wall.

I had some cleaners over to my house to clean the ducts. They found
one section of the main duct (the duct coming out of the furnace) that
was completely blocked with fiberglass insulation. This section of the
duct was just two sections away from the section that connect directly
into the furnace, and there is no other way for the air from the
furnace to reach the rest of the house without passing by this blocked
duct.

I've only had the house a week so I don't know how well it heats in the
winter.

I think I should remove the insulation, but I wondered if anyone out
there might know of any reason why the insulation would be there in the
first place. Obviously someone put it there for a reason (unless it
was a mistake during the original construction).

Thanks!