U-Factor and SHGC Part 1: What Are These Ratings?

U-Factor and SHGC Part 1: What Are These Ratings?

U-factor and Solar Heat Gain Coefficient (SHGC) are the major ratings that determine whether windows can be considered energy-efficient. These measurements can be found on the label provided by the National Fenestration Rating Council (NFRC), which every ENERGY STAR®-certified window should have.

On this first installment of Statewide Energy Solutions’s special blog, learn what these ratings mean and how to use them when choosing energy efficient windows:

What Is U-Factor?

This measurement refers to the ability of a window to insulate heat. It’s expressed in a number ranging between 0.20 to 1.20. Lower digits mean more effective in reducing heat transfer.

U-factor doesn’t only refer to the insulating properties of the glass. The NFRC rates custom windows with the whole system in mind. In other words, the contributions of the framing material, the gas fill and the spacer system are all taken into account.

What Is SHGC?

SHGC pertains to the ability of a window to reflect solar heat. Like U-factor, it’s also expressed in a number except that it ranges from 0 to 1. As with the other rating, lower SHGC values are better.

Does Any Window Possess the Lowest U-Factor and SGHC Values?

In a perfect world, all windows have a U-factor of 0.20 and an SHGC of 1.20. In reality, though, Statewide Energy Solutions attests that even the most efficient products don’t possess these ideal rating levels.

Moreover, lower U-factor and SGHC values can affect Visible Transmittance, which is another rating to consider when tackling window replacement.

Although a compromise is inevitable to attain excellent energy efficiency, ENERGY STAR sets U-factor and SHGC maximums to guide you on your decision.

So, which combination of U-factor and SHGC are ideal for houses in the Dallas-Fort Worth metroplex? Learn about it in the second half of Statewide Energy Solutions’s special blog. But if you like to get your project started, call (214) 302-0557 to get a free estimate in Plano, Texas, or any nearby TX community.


(800) 339-4326/(214) 960-2798