Selecting New Exterior Doors

One common type of exterior door has a steel skin with a polyurethane foam insulation core. It usually includes a magnetic strip (similar to a refrigerator door magnetic seal) as weatherstripping. If installed correctly and not bent, this type of door needs no further weatherstripping.

The R-values of most steel and fiberglass-clad entry doors range from R-5 to R-6, excluding a window. For example, a 1-1/2 inch (3.81 cm) thick door without a window offers more than five times the insulating value of a solid wood door of the same size.

Single-pane glass or “patio” doors, especially sliding glass doors, lose much more heat than other types of doors because glass is a very poor insulator. Models with several layers of glass, low-emissivity coatings, and/or low-conductivity gases between the glass panes are a good investment. Most modern glass doors with metal frames have a thermal break, which is a plastic insulator between inner and outer parts of the frame. When buying or replacing patio doors, swinging doors generally offer a tighter seal than sliding types. Look at NFRC labels to find air leakage ratings. A door with one fixed panel will have less air leakage than a door with two operating panels.

It’s impossible to stop all the air leakage around the weatherstripping on a sliding glass door and still be able to use the door. In addition, after years of use the weatherstripping wears down, so air leakage increases as the door ages. If the manufacturer has made it possible to do so, you can replace worn weatherstripping on sliding glass doors.

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