What are the frames of energy efficient windows made of? It is hard to imagine a frame of an energy-efficient window being made out of aluminum. "It is hard to imagine the frame of an energy-efficient window...
"It is hard to imagine the frame of an energy-efficient window being made out of aluminum, but nothing is impossible," says energy efficient window expert Steven Poitz. "I have seen a drawing of a European window that I would call energy efficient that had an aluminum frame, but I have never seen one in North America. Most frames on energy-efficient windows are wood, vinyl, or fiberglass and the highest energy efficient frames are either vinyl or fiberglass with insulation in the middle," he explains.
Why fiberglass? Fiberglass is a very stable material for windows because it contracts and expands at a rate close to that of glass versus the expansion and contraction rates of vinyl and aluminum. This leads to less air leakage and less stress on the windows mechanisms, especially during cold weather. Fiberglass is also naturally insulating so it does not require a "thermal break" like aluminum frames do. It is also very sturdy and so does not require stiffeners that many vinyl frames do.
The Canadian Government's Consumer's Guide has found that, "The best energy performance in window frames has been achieved using a fiberglass frame with foam insulation in the frame cavities."
Because fiberglass is so strong it also allows for a more aesthetically pleasing appearance since the casements can be smaller and more glass can be exposed. Fiberglass is also preferable as a window frame material because it will not warp, rot, lose its color, shrink, crack, or sag like wood or vinyl frames can.
Fiberglass is a fairly new introduction in the widow industry. It has been available for about 20 years and is just now beginning to gain acceptance as a common construction material. At first only a few innovative manufacturers experimented with fiberglass window frames, but it has now become an industry standard for achieving the highest energy efficient windows possible.
Besides having an expansion rate similar to glass, and being very strong and resistant to rotting, fiberglass also offers the benefits of being paintable and having a low environmental impact in its production. Poitz's company, Thermotech, uses pultruded fiberglass lineals, which is made by a process of pulling continuous strands of glass that have been saturated in thermoset resin through a heated die. This produces the most energy efficient and strongest fiberglass. It is also highly resistant to UV rays without the need for high maintenance coatings. Field tests have proved pultruded fiberglass to be superior in stability, durability, thermal insulation, appearance, and environmental friendliness even in extreme climates.
Another benefit of fiberglass window frames is that they allow the manufacturer to design custom windows very easily. The limitations on glass size are decreased, making large picture windows that are also energy efficient possible. Windows can produce a cold draft for two reasons. One is that they leak air around the frame and the second is that poor insulation allows for cold air to penetrate the interior side of the glass. Highly thermal fiberglass eliminates both of these problems and makes windows of any size possible. Larger windows mean better views and more natural light.
In every way, fiberglass comes out on top as the best energy efficient window frame material. A triple glazed window with a fiberglass frame and low-E coating offers the absolute best protection against heat loss in the winter, condensation, and overheating in the summer.
