Doors
There are several options where energy efficient doors are involved. They are:
Wood Doors:
Excellent insulation in itself
Requires maintenance to protect from weather damage
Tends to be expensive
Steel Doors:
Have built in foam insulation
Strong and resists warping
Less expensive than wood
Fiberglass Doors:
Have built in foam insulation
More expensive than steel, but less expensive than wood
Proper installation of these doors is an absolute necessity. Loose doors without necessary insulation allows heat to escape.
Caulk and weather-strip doors to reduce air leaks and reduce heating and cooling bills.