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Windows: Buyer’s Guide
Window Shopping: Efficiency Expertise
A few facts will save you time help you see your options clearly when buying new or replacement windows. The chart below defines basic terms about energy-efficient windows. If you’re replacing an existing window, you should at least upgrade to an efficient double-pane window, and consider features like gas filling and low-e coating. Look for a window system with a combined low U-factor (0.35 or less is generally suitable for California’s climate) and a low solar heat-gain coefficient (0.3 or less is generally suitable for California).
Energy-Efficient Window Features
|U-Factor||Measure of how well the window prevents heat from escaping. The lower the U-factor, the better its insulating characteristics. Consult the ENERGY STAR® website to find the recommended U-factor for your climate.
||0.2-1.2; lower is better|
|Solar Heat Gain Coefficient||Measure of how well a window blocks heat from the sun. Lower values signify a window that transmits less solar heat. Consult the ENERGY STAR® website to find the recommended solar heat gain coefficient for your climate.
||0-1; lower is better|
|Visible Transmittance||Amount of light permitted through the window. A higher number means more light comes through
||0-1; higher is better|
|Air Leakage||Amount of air movement, in cubic feet, passing through the cracks in the window assembly (cfm/ft). A lower number signifies a tighter window.
||Look for 0.01-0.06|
|Multiple Glazing (panes)||Window assemblies with more than one pane of glass to help prevent heat loss/gain. Look for double- and triple-paned windows.
||Double- or triple-pane|
|Gas Filling||Often used in multiple glazing window assemblies to fill in the space between panes, boosting insulating properties, and inhibiting heat flow. Argon and Krypton are more efficient than other gasses.
||Argon or Krypton|
|Low-Emittance Coating (low-E)||Microscopically-thin, invisible metallic coating, usually on the inside layers of the glass panes. Low-E coatings help prevent heat flow by reflecting invisible, long-wave infrared radiation, thereby lowering the window’s U-factor. .
|Insulating Spacer||Insulating material used as a spacer in the assembly to help prevent condensation. Insulating spacers work better than traditional aluminium spacers.
|Solid Steel and Aluminium||Least efficient frames because they are poor insulators and expand or contract with weather changes. Choose other material, if possible.
||$10 to $15/square foot|
|Wood||A good insulator with minimal expansion and contraction, but requires more maintenance and can get moisture damage. Some wood components are treated with preservatives or are covered in metal or vinyl to decrease maintenance.
||$20 to $30/square foot|
|Vinyl||A good insulator requiring little maintenance, but can be damaged by the sun and elements, leading to peeling, warping and discoloration. Expands and contracts like metal components with weather changes. Sometimes made with a fiberglass core. .
||$15 to $20/square foot|
|Fiberglass||Good insulator with minimal expansion. .
||$20 to $30/square foot|