A standard aluminum frame (common in most homes since the late '50s) is not much better than a hole in the wall -- these frames very efficiently conduct heat to the outside. Although these frames are inexpensive at first, the energy and comfort costs over time make them a poor choice. Modern window frames, like those pictured above, are made with materials such as solid vinyl, fiberglass and vinyl-coated wood. They are also made with better gaskets and seals to prevent the infiltration of outside air.
A single pane of glass offers little resistance to heat flow. Energy bills and comfort are greatly improved with insulating glass, units made of two panes of glass with an air space. It's the air gap between the two panes that does all the insulating.
- Heating and Air Conditioning
Energy costs will decrease with insulating glass since its resistance to heat flow (R-value) is two to six times higher than with single pane glass.
- Comfort and Condensation
Poor windows are cold to the touch in the winter. That is why older single-pane windows feel so chilly and moisture condenses on the frame and glass. The inside surface temperature is as cold as the outside air.
Insulating glass can be further improved with a nearly invisible low-emissivity coating on one of the surfaces facing the air gap. Because this coating reflects heat, more heat stays inside your house during the winter. Low-E coatings can also help filter damaging ultraviolet light.
This heavier-than-air clear gas is used to fill the gap between the panes of glass. It improves the insulating value of the window, especially if a Low-E coating is also used. A gas filled, Low-E window can be as good as a triple pane. An argon option in a window may add about 5% to the cost.
For more information about glazing technology, go to the Glazing Alcove and Glazing Balcony.You might also want to visit the Windows & Daylighting Group's site at Lawrence Berkeley National Laboratory and the Efficient Windows Collaborative web site.