What is Low-E?

Windows are a primary source of both heat loss and solar gain in a building, accounting for up to 25% of energy usage in a home. Clear glass transmits over 84% of infrared energy from a heated space to a cooled space. Single-pane glass easily transmits infrared light and radiant energy, and thus does not provide much of a thermal barrier.

During cooler months, heat from inside a structure is transmitted through glass panes to the cooler outside air. During warmer months, the sun’s rays passing through the panes heat the interior space. This transfer of heat is called emissivity. Reducing transfer of energy from heated to cooled spaces results in lower energy usage and lower utility bills.

There are several ways to minimize emissivity through windows. Double-glazing and special coatings significantly reduce energy exchange through glass. Low emissivity or low-E coatings are microscopically thin metallic layers applied on glass that minimize energy exchange. Long-wave infrared radiation or heat is blocked while short-wave infrared radiation or light penetrates the glass. The resistance to heat flow is called U-value. A well-insulated window has a lower U-value. Double- or triple-hung low-E windows have lower U-values and better energy performance. In northern zones, gas-filled multiple pane windows work well to keep heat in during winter.

The U.S. Environmental Protection Agency’s Energy Star Program evaluates the energy usage of building materials and household products. When purchasing new or replacing windows, look for the Energy Star rating to determine how well these products perform. Ratings by Energy Star are keyed to the climate zones of the U.S., so you can select the best-performing windows for the Fort Wayne area. Windows must meet several criteria to carry the Energy Star label, including the U-value and Solar Heat Gain Coefficient (SHGC). The SHGC shows how much heat from sunlight is blocked.

Emissivity also applies to other materials like roofs. Poorly insulated roofs transfer heat from warm to cooler spaces resulting in heat loss during cold months. You can discuss the benefits of energy-efficient roofing in Fort Wayne with us at Hoosier Windows & Siding, your local, reliable contractor.