New doors can improve the appearance and functionality of your home, but the best ones can be expensive. To maximize the value of your investment, install doors that are energy efficient and that can be affordably maintained. The quality of a home’s doors, and the way they are installed, plays a big role in that home’s comfort and energy performance. Because doors are opened and closed frequently, it’s important to limit the flow of air around the hinges, doorjamb, door sweep, threshold, and weather strip.
There are two kinds of exterior door—the ones like walls and the ones like windows. Wall-like doors are solid; they have little or no glazing, and therefore they transmit little solar radiation. They are usually made of wood and have an R-value of 2 to 2.5. Steel, fiberglass, and composite doors are sometimes filled with insulation; these have R-values of as much as 10.
Window-like doors include sliding glass doors and French doors. These doors have a relatively large tempered-glass area and may transmit a good deal of solar radiation. Some of them have IGUs, with low-e coatings and inert gas. Sliding glass doors with an R-value of 3 and a SHGC of 0.3 to 0.5 can be a cost-effective investment; they are more comfortable and more energy efficient than a single-pane glass door.