We have a forced heating system and all of the rooms but one have warm air blowing out of the vents. Why would colder or cool air be blowing out of the vents in one room? Note that this room is much larger than the other bedrooms so I figured the force of the air might be split between two vents but I'm not sure why the temperature would be cooler than the rest of the rooms in the house. Any thoughts?

Bad install.
Bad damper adjustment.
Disconnected pipe.
Some other form of blockage in pipe.


It is best to follow the duct from furnace to room if possible and inspect for problems.