What Are Warm-Edge Spacers for Windows?

History

• Aluminum spacers were introduced during the 1960s and 1970s as a way to stabilize window panes installed in insulation units. As high-performance windows became more common, manufactures began looking at other materials that provided both structural support and increased thermal resistance. Although aluminum is cheap, durable and lightweight, it transmits heat easily and serves as a poor insulator. One solution was replacing aluminum spacers with metals such as stainless steel, which have a lower conductance. Other warm-edge solutions included changing the spacer’s shape, as well as using silicone, sealers and other materials with high insulation and bonding qualities. Extruded vinyl and fiberglass have also been used as substitutes for aluminum in warm-edge spacer designs.

Function

• Warm-edge spacers sit between window glazings, which are the two or more layers of glass placed into the bottom of the insulation unit. The spacers function as separators between the glazings, spacing apart the glass layers so they are not touching. Like standard spacers, warm-edge spacers serve to interrupt the heat transfer pathway around the edge of the glazing layers.

Types

• Types of warm-edge spacers available on the market vary and include stainless steel spacers, plastic spacers, foam spacers and warm-edge spacers without a metal backing. Manufacturers also produce warm-edge spacers made from high-performance composites such as thermoplastic matrix and butyl-matrix.

Benefits

• Because warm-edge spacers improve thermal performance over aluminum spacers, they increase your home's energy efficiency. The University of Minnesota's Efficient Windows Collaborative estimates that warm-edge-spacer technology will become increasingly important as manufacturers switch from producing conventional double glazing to higher-performance glazing windows. Spacers, which average 2 1/2 inches in size, reduce heat loss not just around the window's edge but also across its entire surface. The collaborative estimates that warm-edge spacers raise a window's bottom-edge interior temperature by up to 8 degrees Fahrenheit compared with aluminum spacers.

Considerations

• Before selecting a spacer system, measure thermal performance against federal energy ratings to estimate your potential energy savings. Though warm-edge spacers are less conductive and perform better than aluminum-only spacers, some contain aluminum or steel encased in rubber. This may influence performance and effectiveness against heat transfer. Also, window spacers containing no metal provide an even lower thermal conductivity than warm-edge spacers. Because these spacers are 100 percent foam, they also insulate against noise and withstand significant structural pressures.