Gas and Oil Home Heating Furnaces - Duct-work needed in walls?

I'm trying to get heat from the furnace in my basement to my (finished) attic. There's one aluminum rectangular duct already which runs up through an interior wall. I'd like to do the same on the opposite side of the house. The problem is that there's an electrical cable running horizontally in the particular wall space I was hoping to use. So my question is do I really need to run a rectangular duct up through the wall or can I simply use the wall space itself as the duct? I'd seal the "duct" in the basement and in the attic. It's an interior wall so I wouldn't need to worry about insulation.

Thanks!
Will

You cannot use a chase (wall cavity) as a supply duct. Try using an oblong duct, it might give you enough leeway to pass the electrical line. If you have central air conditioning through this duct or intend to in the future, insulate the duct. It will sweat just like a cold water pipe in the summer.