No. Code requires a high and low combustion air intake.I wish I could post an image but since this is my first post I am not allowed to post links.
I will try to describe what I am seeing.
I found another vent in the ceiling, maybe it goes out to the roof, and maybe its left behind from the old furnace hookup. If this is true then do you think I could go ahead and cover the lower vent that is letting in all the cold air?
Does your furnace gets its return air through the louvered door, or is it ducted to the furnace. If ducted to the furnace. You can put on a solid door.