Additional Glass Options Include:

• Low-e glazings are special coatings that reduce heat transfer through windows. The coatings are thin, almost invisible metal oxide or semiconductor films placed directly on one or more surfaces of glass or on plastic films between two or more panes. The coatings prevent heat loss during winter and slow heat from entering the house in the summer.
• Spectrally selective coatings are considered to be the next generation of low-e technologies. These coatings filter out from 40 to 70 percent of the heat normally transmitted through clear glass, while allowing the full amount of light transmission.
• Insulated glass contains at least double panes surrounding a sealed air space, offering an insulated layer between you and the elements, plus warm-edge spacers that minimize heat and cold conductivity between outdoors and indoors. Filling the gap between the panes with a low conductivity harmless inert gas adds about another R-1 of insulation value to the window, and also helps block out noise.
• Heat-absorbing glazings are glass that has tinted coatings to absorb some solar heat (but they can’t absorb it all). Some heat continues to pass through the glass by conduction and re-radiation.
• Warm-edge technology uses low-conductance spacers to reduce heat transfer near the edges of insulated glazing. The edge spacers are what hold the panes of glass apart and provides an air-tight seal in an insulated glass window. The better models carry a long warranty against spacer and seal failure. New glazing technologies with warm edges and insulated frames not only reduce energy costs, but make homes more comfortable as well, even helping to reduce incidents of frost and condensation.
• Reflective coatings greatly reduce the transmission of daylight through clear glass. Although they typically block more light than heat, reflective coatings, when applied to tinted or clear glass, also slow some heat transmission. These coatings are commonly applied in hot-climate locations, where protection from the glaring sun is critical to comfort. Care must be taken, though, since the reduced cooling energy that results may be somewhat offset by a resulting need for additional artificial lighting.
• Visual transmittance (VT) identifies the see-through quality of the glass. Windows with high visible transmittance are easy to see through and admit plenty of natural daylight. The VT in residential windows ranges from a shady 15 percent for some tinted glass, up to 90 percent for clear glass (the higher the number, the clearer the glass). To most people, glass with VT values of 60 percent or more looks clear. Any value below 50 percent begins to appears dark and/or reflective. Besides giving you a nice view, high-VT windows can save energy in certain conditions because you’ll need less artificial illumination. But can you have your high-tech insulated glass and see through it too?

Not all of the time. Some tints and coatings that block heat also reduce visual transmission, so make sure you actually see and look through any special glass you may be considering, before specifying it for your home.