Due to improved technology
Windows are becoming more energy effecient
Take a look at the various steps manufacturers have taken along the years to make windows more energy efficient:
Multiple layers of glazing:
In the '80s, some manufacturers only used glass as insulation. Others used a thin film of plastic. There were a few who added layers of glazing to improve energy performance of windows. When manufacturers add a second, third or even a fourth layer of glazing, the insulation vastly improves.
Thickness of air space:
The air space between the two panes of double-glazed windows provides insulation. In the '70s, manufacturers increased the thickness of the air space from ¼" to ½" in double-glazed windows or more. If the air space is increased over 1", condensation forms between the layers of glass and does not increase your energy efficiency.
Low-conductivity gas fill:
The air sealed between the insulated glass windows was replaced with low conductive and dense gas, such as argon (Ar), carbon dioxide (CO2), sulfur hexafluoride (SF6), krypton (Kr), and argon-krypton mixtures in order to reduce heat even more. Argon gas-fill is offered by some major manufacturers as an option.
Tinted glass coatings:
Tinted films were applied to windows to reduce heat gain as well. Unfortunately, the tints restricted visibility and some films bubbled and peeled from the glass. Today, manufacturers use lighter tinting so as not to limit visibility. This improved lighter tinting reduces solar heat and no longer peels away from the window or bubbles.
An even better technology was developed in the '80s -- Low-emissivity (Low-E) coatings. This thin transparent coating of silver or tin oxide is placed on the window and does not restrict visibility or light from passing through the window. By reflecting the solar heat back into the room, the low-e coating reduces heat loss through the windows.
Different climates require different solar gain coefficients --the rate of heat loss in BTU (British Thermal Unit) per hour through a square foot of surface. Southern climates where cooling is important require low-e windows with low heat gain coefficients. In Northern climates, low-e windows with high heat gain coefficients are required.
From an energy perspective, it is suggested that you customize your window installation to allow for different low-E glazings for your home depending on which direction the windows are exposed to. Example: Low-E glass windows with a high solar heat gain coefficient should be installed on the southern exposure of your home. The side with a northern exposure should have the lowest U-value windows installed.
R-values of replacement window materials:
R-values are used to rate how well a material such as insulation resists the flow of heat through it. The higher an R-value is, the more heat loss it resists, and therefore the more energy efficient it is.
- Fiberglass R-Value = 10
- Vinyl R-Value = 6
- Wood R-Value = 5
- Aluminum R-Value = 0.2
Environmental impact is becoming a driving force in window selection.
Fiberglass is environmentally-friendly
- The main ingredient in fiberglass is glass, which is made from sand - an abundant resource.
- Fiberglass windows typically include a certain percentage of recycled material; they last longer and if disposal is necessary, they are inert.
- But most importantly, the manufacturing process of fiberglass windows doesn't tax the environment. The total energy required to produce a product from start to finish is called "embodied energy" and Fiberglass windows have about 80% less embodied energy than aluminum and 39% less than vinyl.