Replace Door Weather Stripping
Inspect the weather stripping around all exterior doors to ensure that it’s present and in good condition. Then, close the door and check for air-leaking gaps around all four edges of the door. Take a peek under the door. If you see sunlight shining through, you’ll need to either raise the threshold or install a door sweep. To detect drafts, take a smoldering stick of incense and slowly pass it around the door, and, if air is leaking in, it will disturb the smoke stream.