Energy Efficient Doors


In addition to their obvious primary function, exterior doors should also function as an effective part of the home's thermal shell or building envelope. Even though they account for a relatively small percentage of the home's overall exterior, in terms of square footage, inefficient doors can contribute to higher-than-necessary space heating and cooling expenses.

The main factors that affect the efficiency of an exterior door are the material the door is constructed from, the tightness of the fit (both between the door itself and the frame and between the frame and the adjacent wall), and the type of glass if the door incorporates a window.

Doors can be constructed of several different materials, including wood, vinyl, fiberglass and metal. Wood doors can be either solid or hollow (hollow doors are intended strictly for interior use between rooms). Most vinyl, fiberglass or metal doors have a layer of insulation, usually some type of foam, sandwiched between the interior and exterior. Check the manufacturer's literature for information on the door's insulating value. This may be expressed as an R-value (resistance) or as a U-value (conductivity). With R-values, higher numbers indicate greater efficiency. Since the U-value is the inverse of the R-value, lower U-values are better. Insulated doors can have R-values of 5 or higher (U-values of .20 or lower).

An efficient door should have some type of built-in weather-stripping to prevent air leakage around the edges of the door. Proper installation also affects the door's overall air-tightness - the joint between the frame and adjacent wall should be caulked or otherwise sealed and any small gaps between the frame and wall insulated. The door's material can also affect the overall tightness. In humid climates, wood doors can swell, making them difficult to close, and in drier weather they can shrink, allowing excess air leakage.

If the door incorporates a window or decorative glass, be sure to check the efficiency ratings for the glass (see "Energy Efficient Windows").

Storm Doors


If your existing door is in good shape, a storm door can be a cost-effective alternative to replacement. A good quality storm door, properly installed, can improve the efficiency of your primary door by creating an insulating air space and by providing an additional barrier to air leakage.

Most storm doors are sold as pre-hung units in standard door widths, and are relatively easy to install. Some have full-height glass panels that maximize light and views while showing off the primary door. Others have a solid panel on the lower half, usually wood clad with metal or vinyl, with glass on the upper half. Most include some type of window and screen system, with various options for replacing the glass with the screens for ventilation in warmer weather.

When purchasing a storm door, check how tightly it fits in the frame, how solid it feels and how smoothly it opens and closes. Be sure to check the warranty as well - less expensive storm doors typically have a five-year warranty, while the best ones offer a limited lifetime warranty.

Caution:

If your primary door has a vinyl coating, check with the manufacturer before installing a storm door, particularly one with full-height glass. In summer, if the window is exposed to direct sunlight, the vinyl coating may be damaged by heat build-up between the storm and primary doors.

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