If one room of your house seems to be chillier than the rest, it is most likely an insulation issue. There may be leaks and cracks in the walls, floors, windows or near doors that need to be plugged. To insulate a cold room, start by diagnosing how the air from inside is getting in, then taking a trip to a hardware store to pick up a few supplies.
Walk around the cold room with a lit candle (you can also use a stick of incense, streamer or feather that will move when air blows against it). Place the candle near the doors, windows and cracks in the room. If the light blows around or goes out suddenly, you have found the cold air leak.
Caulk the draughty openings in your windows. Fill them with a thick line of the caulk, and then use a paint stirring stick to push the caulk in before it dries. Add as much as you need to fill the crack thoroughly.
Put plastic sheeting up over the windows in the room. Place double-sided tape on the inside of the frame, then use your fingers to slowly secure the edges of the plastic sheeting to the tape. Run a hair dryer on medium heat over the plastic where it is held in place by the tape (the heat will meld the tape to the plastic) then quickly run it over the centre of the plastic so that it will tighten.
Buy a draft guard or stopper for your door to stop air that is leaking in from the bottom. You can also nail a rubber door sweep to the bottom of the door as an alternative.
Use foam insulation tape to cover the leaks around the other edges of your doors. These strips have adhesive on one side so that you can easily attach them to the doorways. Open the door all the way, and line the inside frame of the doorway with this foam insulation. Close and open the door a few times when you're done to assure that it fits snugly into the insulated frame.
Check for cracks in the floor that could lead down to a basement. Cold air in the basement will move up through a crack to that room. Seal the cracks with your caulking gun as well, and be sure to insulate your basement next.