Stop drafts coming under a door by raising the adjustable threshold. It only a minute to turn the four adjusting screws.
Raise the threshold until you no longer see light gaps under the door.
Those big screwheads in the threshold of a newer entry door aren't just decorative; they raise or lower a narrow strip set in the threshold. So if you've noticed a draft under the door, try this: On a sunny day, turn off the lights and close nearby curtains. Lie down and look for daylight under the door. A sliver of light sneaking in at both corners of the door is normal. But if you see light between the threshold and the door, grab your screwdriver. Raise the threshold where light enters by turning the nearest screws counterclockwise. Set a straightedge (such as a framing square) on the threshold and adjust the other screws to make sure the adjustable strip is straight. Close the door and check for light. Readjust the threshold until you've eliminated the light. But don't raise the threshold so high that it presses too hard against the weatherstripping on the door. A too-tight fit will wear out the weatherstripping quickly.