Visual inspection and smoke pencil testing showed that a significant amount conditioned air is migrating in or out through gaps between doors and their frames. This leads to drafts and discomfort in the door area, and also allows heating or cooling energy to escape.
Weather-stripping of doors, including sweeps on the bottom, is one of the most cost-effective energy conservation measures. However, no weatherstrip lasts forever and life expectancy is especially short around high-use doors. So only commercial grade products should be used, and replacement should be a regular maintenance item (generally every one or two years in high traffic doorways).
The following doors should be taken care of as soon as possible: