You’ll also want to check the compression abilities of existing weather stripping. Go outside and close and latch each door. See if the weather seal compresses. The tan strip in this photo is the weather seal. You should see the seal compress about halfway when the door closes. Sometimes the seal is there but does not compress enough to be effective.

You can tell that weather-stripping is compressed enough when you no longer see light coming in around the perimeter. If you see light, you’ll need to either enlarge the weather seal or adjust the strike plate on your door to get the door to close tighter. If you replace the weather stripping and your door has a groove, get the type that fits into the groove, since it will last much longer than the peel-and-stick type.

Under doors. The underside of the door is a notorious spot for air and water leaks, since the rubber sweeps that form the seal at the threshold wear down over time from rubbing.

If your threshold has large visible screws, you may be able to turn them to adjust part of the threshold upward to get a tight seal. If not, slide on a U-shaped metal sweep, adjust it so the door closes easily but seals well, then screw it into the face of the door to attach it. These sweeps can often be installed without your having to remove the door.

Because doors get a lot of abuse, a quality weather seal means you won’t be redoing this every year. If you do use the peel-and-stick variety, make sure to clean the door and jamb well before applying, both where the piece will attach and where it will hit the door.