Keep cold from coming through the door

The old dollar bill trick - putting a dollar in the door of the refrigerator and closing it, then seeing if it pulls out - works on exterior doors on your home, too. (You can substitute a piece of plain paper.) Hold a paper on the door frame and close the door. If it falls to the floor or comes out easily when you tug gently on it, put in new weather stripping. If it resists coming out, the door fits the frame close enough to keep out the winter cold.