968 Doors

In general, door U-factors can be determined in a similar manner to the walls, roofs and exposed floor demonstrated above. Softwoods have R-values around 1.0 to 1.3 per inch, while hardwoods have R-values that range from 0.80 to 0.95 per inch. A 1-3/8-inch panel door has a U-factor of approximately 0.57 Btu/(Hr-ft2-°F), while a 1-3/4 solid core flush door has a U-factor of approximately 0.40.

As has been shown to be the case with some walls and windows, metal doors are a different story. The same issues affecting windows, such as framing and thermal break apply to metal doors as well. The U-factor of a metal door can vary from 0.20 to 0.60 Btu/(Hr-ft2-°F) depending on the extent to which the metal-to-metal contact can be "broken." In the absence of tested door U-factor data, Table 6 page 24.13 in Chapter 24 of the 1997 ASHRAE Handbook of Fundamentals can be used to estimate the U-factor of typical doors used in residential and commercial construction.

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