My wife and I had noticed that our bedroom never seemed to be particularly hot or cold.
I looked into it last weekend and found that the last home owner had put a huge diverter in the duct leading to the master bedroom to send heat into the basement over his work bench. There was probably 1.5" of the duct still open to our room.
They cut a 6*8 duct down to a 1.5*8 duct.
This explains why the basement has been extra cold since we added central air, and why our bedroom never seemed quite right.
And for bonus points, they hand made the register out of 1/4" plywood with slits cut into it, and to close it off, they shoved some sheet metal between the duct and the register. Apparently Menards (2.5 miles away) was just too far to go.