Doors are necessary for access and often for ventilation and illumination too. However, if they are in poor condition (or just very old) they can contribute to high amounts of air leakage and related energy losses.

Exterior Door Replacements
Modern exterior doors often fit and insulate better than old ones, and their associated heat losses (or gains) come from opening and closing the door. However, damaged weatherstripping can increase energy loss around the door by many times. Check your weather-stripping every year and replace it as needed. After replacing the weather-stripping, check the door seal again. If the door still does not seal tightly to all sides of the jamb either you installed the weatherstripping badly or the door is bent and in need of replacement.Consider an insulated metal or fiberglass door when replacing exterior doors. They are a better investment than wooden doors since they are much more durable, have lower maintenance needs and seal and insulate better. They also have the added advantage of offering more of a deterrent to intruders. Most insulated door prices range from $200 to $400. One common type has a steel skin with a polyurethane foam core; they usually have a magnetic strip (similar to a refrigerator door magnetic seal) for weather-stripping. If installed correctly, and if the door is not bent, this type of door needs no further weather-stripping. The R-values of most steel and fiberglass clad entry doors range from R-5 to R-6 (not including the effects of a window.) For example: A 1-1/2 inch (3.81 cm) thick door without a window offers better than five times the insulating value of a solid wood door of the same size. When you buy a door, it will probably be pre-hung frame. Pre-hung doors usually come with wood or steel frames. In most cases, you will need to remove the existing doorframe from the rough opening before you install a pre-hung door. The doorframe must be as square as possible, so that the door seals tightly to the jamb and swings properly. It is a good idea to use expanding foam caulking to seal the new doorframe to the rough opening and threshold to prevent air from getting around the door seals and into the house. You should do this before adding the interior trim.

Storm Doors Adding a storm door that costs about $200 or less is generally a good investment if your existing door is old, but still in good condition. However, adding a new (or more expensive) storm door to a modern foam core door is not generally worth the expense since the added energy saved is very small. But you may have aesthetic reasons for wanting a storm door anyway. In any case, never add a glass storm door if the door gets more than a few hours of direct sun each day. The glass will trap too much heat against the entry door and possibly damage it. Storm doors for patio doors are hard to find but they are available. Adding one to a modern multi-glazed energy-efficient low-e door is seldom economic. Insulated drapes, when closed for the night in the winter (or on sunny days in the summer) are also a good idea. High quality storm doors and windows use low-e glass. Frames are usually made of aluminum, steel, fiberglass, or wood (painted or not). Wooden storm doors require more maintenance than the other types. Metal-framed storm doors and windows might have foam insulation in their frames. Some doors have self-storing pockets for the glass in summer, and an insect screen for the winter. Some storm windows have fixed, full length screens and glass panels that slide out of the way for ventilation. Others are half screen and half glass; these two components slide past each other. Some are easily removed for cleaning, others are not. All of these features add some convenience and higher costs.

Source: U.S. DOE, Energy Efficiency and Renewable Energy Network, Consumer Energy Information: EREC Reference Brief. EREC is operated by NCI Information Systems, Inc. for the National Renewable Energy Laboratory/U.S. Department of Energy. The content of this brief is based on information known to EREC at the time of preparation. No recommendation or endorsement of any non-U.S. Government product or service is implied if mentioned by EREC.