Measuring Energy Efficient Windows

When you’re ready to invest in energy efficient windows, it’s always smart to look for the Energy Star label. The information on each window’s NFRC label allows you to look deeper to find the best match for your particular needs.

Thousands of window, door and component manufacturers belong to the National Fenestration Ratings Council their submission are rated for energy efficiency. West Coast Vinyl windows all have the NFRC label. The NFRC’s distinctive label on each of its members’ windows rates several categories – different features can be more important in your particular situation, but in general all the ratings measure how well the window keeps the inside in and the outside out.



Here is the breakdown of what the sticker mean.

The U-Rating measures how well the window keeps heat from escaping – an especially big issue in the winter when you want to keep that expensive heat indoors. The lower the number (on a range between 0.20 and 1.20), the less heat escapes.

The Solar Heat Gain Coefficient measures how much heat the window lets in with the light – particularly of interest in those southwest-facing windows, perhaps. When you want to keep the A/C bills low, look for windows with a low solar heat gain coefficient.

Visible Transmittance measures (on a scale of 0-1) how much light the window allows to pass through; the higher the number, the more light is transmitted.

Air Leakage looks at one of the biggest culprits in a home’s unwanted gains and losses of heat: flow of air through less-than-perfect seals and other joints on the windows. The lower a window’s AL number, the less air it lets through.