To save heat in the winter and air conditioning in the summer, check your home’s doors to the outside. A gap as small as one-eighth of an inch can let in as much outside air as a 2½-inch hole in your wall!
To correct this problem, check the threshold beneath the door. That threshold should have a removable cap. Underneath that are screws. Turning them counterclockwise will raise the threshold. To check if its high enough, place a dollar bill on the threshold and close the door. If the threshold is at the correct height, you should not be able to pull out the bill, but the door should still close and open easily.