You may have encountered the terms U-value and solar heat gain coefficient (SHGC) when shopping around for replacement windows. You might think that these terms are one and the same, but they’re two different energy performance ratings that help homeowners determine whether a window is energy-efficient enough for their needs. Learning the differences between the two allows you to make informed decisions as you purchase new windows. 


The U-value of the glass is one of the most important ratings to look at when buying new windows. The U-value or U-factor of a window measures how quickly it transfers heat that doesn’t come from the sun. In short, it shows how well the window insulates and how well you can measure that. The U-rating of a window is shown as a number between 0.2 and 1.2. The lower the U-value, the less heat the glass will transfer, making your home better insulated. In general, it’s best to find glass with the lowest U-rating because it will help people make better use of their heating.

Solar Heat Gain Coefficient 

SHGC is a way to figure out how much heat from the sun gets through a window or door. The less heat it lets in from the sun, the lower the number. When windows have a high SHGC, they let more solar radiation pass through, absorbed and eventually released inside the house. This means that these glass units make your house or building get hotter more quickly. For energy reports to be valid, the SHGC must be within 10% of the set value. SHGC is written as a number from 0 to 1. The SHGC rating can be very different depending on the type of glass.

How Do These Values Help Windows?

Windows with ideal U-factor and SHGC values resist solar heat gain. In the winter, solar radiation offers free heat for the home. However, it leads to overheating in the summer and greater energy expenses as you adjust the thermostat. Older windows lack these energy-efficient features. Windows with high U-factor values and failed assemblies cause:

  • Increasing internal temperatures

  • Loss of heat and coolness

  • Heater to work too hard

  • An increase in monthly electricity costs

Installing low-U-factor and SHGC windows solves most energy problems. Window installers can also identify gaps and cracks that lead to heat and cooling loss. In addition to installing energy-efficient windows, they’ll insulate the building to avoid heat loss or gain.

When it comes to siding or roof replacement, look no further than Tri-County Contracting. Our expert team also provides window and door services, and we strive to give our clients a smooth installation experience. Get started with your window consultation today by filling out our contact form or calling us at (262) 217-8150. We serve homeowners in and around Waukesha, WI.