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Fiberglass doors are a more efficient option compared to wood

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Insulated fiberglass door with brass trim and leaded glass

Dear Jim: I like wood front doors, but mine is leaky and needs refinishing. I would like something more maintenance-free. Are stainable fiberglass doors more efficient and durable and do they look like wood? - Sharon G.

Dear Sharon: Real wood entry doors are the most attractive, but as you found, even high-quality ones require regular maintenance and eventually need replacement. A stainable or painted fiberglass door filled with foam insulation is attractive and more efficient than solid wood.

Since many new styles of front doors have much decorative glass, the efficiency of the glass inserts is more important than the insulation value of door material itself. Still, any insulated area is better than the solid wood.

I have insulated fiberglass double front doors on my house. With a large decorative window in each panel and supporting wood stiles (vertical) and rails (horizontal) edge supports, less than 40 percent of the door is actually insulated. Doors with smaller windows would have been better for security and efficiency.

Air leaks around an old warped door are generally more of an efficiency issue than the insulation value of the door construction itself. If you can actually feel the air leaking in around the door, it is in really bad shape. Most often, you need to hold a stick of lighted incense or a candle near it to detect the air movement through leaky weatherstripping.

Insulated fiberglass doors remain airtight over their life. Since fiberglass is basically glass fibers in a polymer resin, it does not absorb moisture and does not swell. If a darkly stained fiberglass door is exposed to the hot sun, the hot side can expand and make it bow, but it quickly returns to its initial shape when it cools.

A properly stained fiberglass entry door is difficult to distinguish from real wood until you actually feel it. Natural wood grained rollers press deep graining into the fiberglass surface. Its weight is much less than a real wood door so hinges wear less and remain true.

All fiberglass door manufacturers offer staining kits for their doors. It is best to use a kit from the manufacturer because there may be something unique about its surface material. Fiberglass is very durable, but the stained finish will fade over time if exposed to intense sun. When restaining, always use a new staining kit because there is a limited shelf life for the old kit materials.

As you shop for a fiberglass door, you will hear salesmen tell you the type of insulation is important. Some manufacturers use preformed foam panels which are placed inside the skins before assembly. Others inject foam in the finished hollow door. There is not a great difference in the efficiency of these systems.

The best option for decorative glass in the door is triple panes which result in two insulating air gaps. One of the most efficient is a decorative plastic pane between two flat glass panes. This makes it easy to clean; more secure from break-ins; and look like real beveled or leaded glass.

The following companies offer fiberglass entry doors: Jeld-Wen, (800) 535-3936,; Pella, (877) 473-5527,; Plastpro, (800) 779-0561,; Taylor Door, (800) 248-3600,; and Therma-Tru, (800) 843-7628,

Dear Jim: When I read books about energy conservation, I often come across the term "thermal bridge". From the context, I assume that it is not good. Exactly, what is the meaning of a thermal bridge? - Rae K.

Dear Rae: You are correct - a thermal bridge is not a good thing. The term refers to a gap in the insulation material around the living area of a house. For example, wood studs inside an insulated wall are thermal bridges. Heat flows through thermal bridges much faster than through fiberglass insulation.

In contrast, a thermal break is a gap in a heat transfer path and is good. An example is insulation or a vinyl strip separating the indoor and outdoor halves of an aluminum window frame.

Send inquiries to James Dulley, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit


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