Steve Barker wrote:
How would it "suck in" CO? there would have to be a CO leak to begin with
and that has nothing to do with the 8x8 hole that is probably just the
return for that particular area.

Depending on air circulation in the area, a danger exists of exhaust
gases being drawn into the air return. For that reason, a forced air
furnace installed in a closet often must have a combustion air supply
separate from the living space.