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Window Energy Efficiency Ratings Explained

Energy Efficient WindowIn the market for new windows? How exciting! These days, energy efficiency is a priority for most consumers but trying to make sense of all the terms and ratings can be confusing.

Let our handy guide help clarify window efficiency ratings.

U-Factor-Therate at which a window conducts non-solar heat flow. U-Factor measures how well a window prevents heat from escaping to the outside. The lower the U-factor, the higher the efficiency of the window.

Solar Heat Gain Co-Efficient (SHGC)-The fraction of solar radiation transmitted through a window. This can be through direct transmission of heat or absorption of heat. SHGC measures how well a window blocks heat from the sun. The lower the SHGC value, the lower the amount of solar heat transmitted through the window.

Air Leakage-The rate of air movement around a window. A window with a low air leakage rating is tighter compared to windows with high air pressure ratings.

Visible Transmittance (VT)-The fraction of visible sunlight that is transmitted through the glazing of a window. The higher the VT rating, the more visible light that is transmitted through a particular window. The VT you will need depends on a home’s daylighting requirements. Since personal preferences vary here considerably, it is best to talk to a professional to help determine the VT rating that will meet your needs.

Light to Solar Gain (LSG)-The ratio between SHGC and VT.  This ratio provides an indication of the relative efficiency of different windows in transmitting daylight while blocking the solar heat. The higher the ratio number, the greater amount of light transmitted without excessive heat.

Shopping for energy efficiency windows requires some savvy. By educating yourself on the above terms, you will better understand what your priorities are for replacement windows. Still have questions? Pacific Home and Patio is here to help you pick out the windows that are right for your needs and budget. Call us today with your energy efficiency window questions in Boise, Meridian, Eagle, and Southwest Idaho as well as Ontario, Baker City and Eastern Ontario.