The most efficient doors have the following attributes:
• cores with high insulating values
• wood, vinyl, or thermally broken metal frames
• weatherstripping made from high-performance materials
• low air leakage rates (for pre-hung door systems)
• windowless or windows with a high Energy Rating (ER)
Depending on style and insulation material, for example, metal-clad doors are more efficient than solid wooden doors.
Heat may be lost between the door, frame, and sill, through glass in patio doors or doors with windows, and between the door frame. Heat loss through doors can be reduced through careful choice of the door, its location, and proper installation and maintenance.
Both solid and sliding glass doors have an Energy Rating (ER); the higher the number the more efficient the door.
Properly designed and installed storm doors will provide some degree of increased efficiency, as well as protection from the weather. Screen inserts provide summer ventilation.