965 Spacers

Double and triple pane window units usually have continuous members around the glass perimeter to separate the glazing lites and provide an edge seal.

These spacers are often made of metal, which increases the heat transfer between the panes and degrades the performance of the glazing near the perimeter. ASHRAE reports this conductive region to be limited to a 2.5-inch band around the perimeter of the glazing unit, and appropriately describes it as the "edge of glass." Obviously, low conductivity spacers, such as plastic, fiberglass or even glass, are to be preferred over high conductivity spacers, such as metal. The impact of highly conductive spacers is only felt to the extent that other high performance strategies are incorporated into the window. For example, ASHRAE reports no significant performance difference between spacers types when incorporated into window systems with thermally unimproved frames. When thermally improved or thermally broken frames are incorporated, the spacer material becomes a factor in overall window performance.

The best performing windows will incorporate thermally broken frames, non-metallic spacers between the panes, low-emissivity coatings, or low conductivity gases, such as argon or krypton, between the panes.

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