I bought an older house and it has a rectangle hole in the living room. It is covered with the register and it looks like an intake. I don't fully think it was used as an intake as the furnace is on the opposite side of the house. The house doesn't have the basement but only a concrete slab.
So there is wooden frame that holds the floor build on the concrete slab. This whole frame is in the shape of L and the missing part consists the furnace area. So the furnace area is not sitting on the wooden floor but directly on the concrete slab.
I'd like to know if there is a reason for that hole? There is a moldy smell coming out in my living room and I was wondering if I could just cover it. The hole look dry and I don't see any wetness in there...