The bedroom on the third floor of my house has floor one floor vent for supply and one for return. In the summer, the central AC works extra hard but yet the bedroom is only about 75% cool compared to the rest of the house. I reckon the cold air coming out of the single supply vent flows along the floor without rising to the bed level and pours out of the bedroom down the stairwell into the house below. I say this because there is quite the pressure gradient between the second floor and the top of the stairwell on the third floor since its really hot in that stair well. All the hot air from the house is collecting there.
I am going to block the bottom of the bedroom door with towels or put weather strips. But I wanted to know if I can run a makeshift duct from the floor vent to the ceiling of the bedroom so that the cold air at least cools the room as it rushes toward the stairwell instead of flowing along the floor. It wont be pretty and it will be visible, but that is something I can live with.
What materials would I need to properly cover the vent and run a duct to the ceiling? I would appreciate any insight to this matter. Thank You
I have added a schematic diagram of the room with dimensions including the dimension of the vent which is 12 inches x 6 inches. The height of the room is 12 feet. I guess I have more of a fluid dynamics question now. Whether I use register boosters or duct guides, is it realistic to expect the dense cold air to fan out as it heads to the floor? Or would it just stream back to the floor in a columnar fashion?