Layers of Glass and Air Spaces – Some Terms to Know:
R Value: An R-value is a unit of thermal resistance for a particular material or assembly of materials (such as insulation). The R-value depends on a solid material’s resistance to conductive heat transfer AKA a measure of the ability to resist heat traveling through it. (The higher the R-Value the better the thermal performance of the window.)
Glazing: Any window glass within the entire construct of the window. The glazing is mounted on the surface of a window. Glazing is commonly used in low temperature solar thermal collectors because it helps retain the collected heat.
Pane: The pane is a single piece of window glass separated by pieces of the window itself. A residential window typically has 1-2 panes.
Single pane windows have very little insulating value with (approximately r-1). It provides only a thin barrier to the outside and can account for a considerable amount of heat loss and gain.
Double-pane: To improve upon single-pane window’s energy efficiency, the number of window glass panes in the unit is doubled. Multiple layers of glass increase the window’s ability to resist heat flow.
Replacement Windows Rating Types of Glass
There are various types of window glass manufacturers use in constructing windows.
Clear glass: This is the primary material available for window panes in homes. In recent years, the market for glazing, cutting, and fitting window panes into frames has changed significantly. Now there are several types of special glazing available that can control heat loss and decrease condensation.
Low-emissivity (low-e) glass: Low E is a special surface coating to reduce heat transfer back through the window. These coatings reflect 40% to 70% of heat normally transmitted through clear glass, while allowing the full amount of light to pass through.
Heat-absorbing glass: This type of window glass contains special tints that allow it to absorb as much as 45% of the incoming solar energy, reducing heat gain. Some of the absorbed heat, however, passes through the window by conduction and re-radiation.
Reflective glass: A window that has been coated with a reflective film is useful in controlling solar heat gain during the summer and, like heat-absorbing glass, it reduces solar transmittance.
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