Exterior doors should have a U-factor of 0.35 or less. In general this requirement is met with a steel door with an insulating foam core. Glass doors must have a U-factor of 0.38 or less.

In existing homes, make sure your exterior doors close tightly. Weather-stripping material such as Xtreme ® rubber or VSeal ® is easy to use and extremely cost effective. Door sweeps can easily be added to prevent drafts at the bottom of doors. Caulk any cracks between the door frame and walls.