We have a two story home with 3 bedrooms upstairs. Home is 7 years old. One of the bedrooms is always around 5-6 degrees Fahrenheit colder than the rest of the house (when compared to the thermostat temp). Currently it is the baby's room and we placed a heater in there to bring up the temp to a comfortable level. I would really like to find a better solution as when the baby is not in the crib anymore we would not want the heater in the room.
There is one vent in the room (which is also true for the other kid bedroom that does not have this problem). The difference between the two vents is that the cold room went is running inside the drywall of the exterior wall and the other room vent is in the floor (but still against the exterior wall, just not in the drywall). The temperature coming out of the went in the cold room feels warm so I know the heat is getting there.
My first thought was to adjust the air flow in the vents going upstairs by closing some of the other vents thorough the house. But I have read that doing this will make your furnace work harder and less efficient since you are altering the origional design/installation. We are the second owners of the house and I am not sure if the room was originally not insulated properly, but I would prefer not to have to open up the walls if it is possible.