An In-Depth Look at U-Factor and Solar Heat Gain

When you decide on a window replacement project, you’ll most likely encounter new units with the small NFRC (National Fenestration Rating Council) label on them. This label allows you to compare different energy-efficient windows, providing you with energy performance ratings in multiple categories. This information helps you determine the most suitable ENERGY STAR®-approved units for your home.

An In-Depth Look at U-Factor and Solar Heat Gain

In today’s post, Renewal by Andersen® of Houston expands on two of the categories found in the NFRC label: the U-Factor and the Solar Heat Gain Coefficient (SHGC).

The U-Factor

The U-factor is an important indicator of energy-efficient windows. It refers to the thermal conductance of a material, telling you how well it insulates or how effective it is in allowing heat flow. In the case of windows, it specifies the amount of heat lost as it passes through the units.

According to the NFRC, U-factor ranges from 0.20, which is the most energy-efficient, to 1.20, the least energy-efficient. When looking for new windows, be sure to look for low numbers since it means that the windows have better insulation.


Solar heat gain, meanwhile, is a material’s ability to block heat from the sun. In the case of windows, it is imperative for these units to allow only a specific amount of the sun’s energy to enter your home. Indeed, windows that transmit almost all of the solar heat may dramatically increase the heat inside your home.

SHGC has a rating between 0 and 1, with the former indicating the least amount of solar heat gain that can come through a window. Same with the U-factor, look for lower SHGC ratings as they indicate the windows’ ability to transmit less solar heat.

To help you understand energy-efficient windows better, seek the advice of the professionals from Renewal by Andersen of Houston. Call us at (281) 547-6177, or fill out our contact form for a free in-home consultation. We serve residents of Houston, TX.