Tom Shafer

Energy-efficient doors give Old Man Winter the cold shoulder

December 07, 2011

Most entry doors are made of one of three materials: steel, fiberglass or wood. Of the three, wood actually has the highest U-value, which means it conducts your heat literally "out the door" in winter and welcomes it into your home in summer. Steel is also a poor insulator, but steel and fiberglass doors are both manufactured with a urethane core, which makes them a better choice than wood. Both steel and fiberglass doors have a U-value of .14, while wood, by comparison, is a staggering .58! Remember, the higher the U-value, the less insulation your door provides from the temperature outside.

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So what about your elegant glass entrance doors? Will good looks keep you warm at night?

How energy-efficient is decorative glass?

Glass for entrance doors is available at both extremes of the energy-efficiency spectrum, from single- to triple-glazed. Like wood, however, glass is also a poor insulator. The introduction of glass lites in your front door might be an elegant touch, but what does it do to the door's insulating properties? How much energy efficiency you lose will depend on the size and composition of the glass.

A full, clear single pane in a steel or fiberglass door raises the door's U-value to .35 or .33, respectively. But consider decorative glass, which is triple-glazed. Made like a sandwich with leaded glass in between two panes of tempered glass, it could increase either a steel or fiberglass door's U-value from .14 to only .27. What about a wood door that has a U-value of .58? Adding decorative glass actually helps it's overall U-value by reducing it to .43. And low-e packages are available for the glass, too. They can improve some doors' insulation ratings enough to meet Energy Star requirements in all four U.S. climate zones.

Material

Without glass

With decorative glass

With clear glass

Fiberglass

.14

.27

.33

Steel

.14

.27

.35

Wood

.58

.43

.68

*U-values of doors with and without glass lites

What else affects a door's energy efficiency?

In addition to your door's composition, take note whether there is a draft coming from the door. If your door does not hang straight in its frame, air infiltration can decrease its thermal effectiveness. If more air is leaking than desired or the glass is too cold, installing a storm door can help.

When both design and energy-efficiency are priorities for your entrance door, you should seriously consider buying a door with better insulating features. Old Man Winter will be knocking before you know it, and you probably don't want to let him in.

*U-values for Therma-tru steel and fiberglass doors, and Simpson wood doors

About the Author

Tom Shafer has decades of experience in window sales, marketing and product development. He's worked closely with window design engineers in testing, design, and building code interpretation. Past employers include United Windows and Doors and Norandex, MI Windows. He currently works at a home improvement retailer.


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