Energy Efficiency

Our High-Performance Insulated Glass Unit (IGU) Contains:



A low-emissivity (low-e) coating is applied to on one of the two panes of glass contained in our IGU. A microscopically thin metallic, transparent pyrolytic layer, low-e allows for optimal transmission of more than 70% of the sun's available light. With all this visible light, your home stays bright. Simultaneously, low-e prevents the transfer of invisible UV and infrared light, protecting your interior from UV damage.Viwinco IGU comparison diagram



An odorless, colorless, nontoxic and heavy inert gas that has excellent insulating properties,  Argon gas fills the dead air space created by the double panes in an IGU. Its low conductivity
is great for thermal performance.

After the unit is filled with the gas, it’s hermetically sealed. In addition to increasing thermal efficiency, argon gas contributes significantly to sound reduction.



The spacer is a vital part of the IGU. It acts to separate the glass panes, but it also works like an insulating barrier at the edge of the unit. Without it, heat might flow from the inside pane, which is necessarily warmer, to the outside pane. A warm-edge spacer is just that: warm at the edges. Constructed from stainless steel for low conductivity, the spacer we use effectively stops the transfer the heat, thus saving energy.



All of Viwinco's thermal testing is conducted by Architectural Testing, Inc. (ATI), an independent test facility approved by the National Fenestration Rating Council (NFRC). There, a thermal chamber is used to provide accurate data on heat transfer through different materials used in the construction of our windows. Standardized methods are employed to test the complete window assembly—the glass, frame, spacers, and other permanent components of the product—rather than parts alone, producing authoritative ratings for the following:

  • U-Factor
  • Solar Heat Gain Coefficient (SHGC)
  • Visible Transmittance (VT)
  • Air Leakage

The ratings for U-Factor, SHGC, and VT are displayed on the NFRC Label, which you can find on all of our products. These tests are required by the Environmental Protection Agency (EPA) in order for a window to be eligible for ENERGY STAR qualification. ENERGY STAR-certified products provide energy efficiency, help protect the environment, and contribute to lower heating and cooling bills. Approximately 95% of Viwinco's products meet current ENERGY STAR performance requirements.

Viwinco Testing Wall



U-Factor was established by the NFRC as an objective way to rate a window’s insulating value.The lower the u-factor of a window, the more it will resist heat flow, and the better it will insulate your residence or other building. Low u-values are most important in colder environments, where the aim is to minimize the amount of heat that escapes and therefore lower heating costs. In warmer or hot climates, a higher U-factor can be beneficial. Higher U-values make it more likely that cool, air-conditioned air won’t transfer out of your home, and that heat won’t transfer in. Thus, air conditioning bills can be kept down.



A measure of how much solar heat enters through a window. In colder climates, a higher solar heat gain is desirable; in warmer climates, the reverse is true. SHGC is measured on a scale of 0-1, with 0 denoting the lowest SHGC and 1 denoting the highest. This rating is also included on the window's NFRC label.



A relative amount of visible light transmitted through a fenestration product (including the frame, which has no visible transmittance) with theoretical range from 1.00 to 0.00. The smaller the number, the less visible light is transmitted. The higher the number, the greater the contribution to daylighting potential.



This is an optional field for manufacturers, not required by the NFRC.The lower the number, the more effectively the window keeps air out.

The following variables affect the data described above:

  • The use and level of low-emissivity (Low "E") as opposed to clear glass: low-e glass is coated with a microscopically thin metallic layer that allows the short wave light energy to pass through as it blocks long wave ultraviolet and infrared solar energy by reflecting it back toward its source (toward the outside in summer and toward the inside in winter)
  • Reinforcement used
  • Color of glass
  • Laminate

View our Air Infiltration, Structural, Water Penetration, Forced Entry, and Impact Tests here