Window U-Factor and SHGC: What Are the Differences?

If you’ve been comparing replacement window options—energy ratings, in particular—you may have come across the terms U-factor and SHGC. In today’s post, local window and roof replacement contractor Pritchett Roofing Inc. discusses the differences between these two energy ratings and their role in choosing the right replacement windows.

What Are Energy Ratings?

The National Fenestration Rating Council (NFRC) provides certifications to fenestrations – replacement windows, entry doors, and skylights – after performing energy performance tests. Ratings that indicate how well a window performs in terms of insulation, heat gain, light transmittance and air leakage can help homeowners choose the right replacement windows for their home.

ENERGY STAR®, an organization that provides certification for a wide range of products that include electronics and siding, utilizes NFRC energy ratings when certifying fenestrations.

U-Factor and SHGC

The two main energy performance ratings on NFRC labels are U-Factor and SHGC:

• U-factor measures a product’s insulating capabilities, particularly in how well it can keep heat from escaping a room. It’s represented as a value between 0.20 to 1.20. The lower the number, the better the product is at keeping heat indoors. Some replacement windows may have an R-value instead of a U-Factor. While both measure a product’s insulation, R-value measures thermal resistance. Therefore, a replacement window with a low U-factor will have a correspondingly high R-value.

• SHGC stands for solar heat gain coefficient. It measures how well a product can resist unwanted heat gain from sunlight and is represented as a value between 0.0 and 1.0. The lower the SHGC value, the cooler your home will be during the summer season.

Which Ratings Are Right for You?

Choosing replacement windows isn’t a one-size-fits-all solution – you must take into account factors such as the local climate, window orientation, and even your personal preferences. Homes located in climates that have both hot summers and cold winters will want windows with low U-Factor and SHGC values. In comparison, homes in predominantly cold climates will want high SHGC values to supplement their heating.

Window orientation will also affect how much sunlight gets into the house. Walls that face east-to-west receive more direct sunlight, and therefore more solar heat. Windows installed on these walls, therefore, need to have low SHGC values with low visible transmittance values to tame the harsh lighting.

Pritchett Roofing Inc. is your leading provider of roof repair and window installation services. Give us a call at (770) 345-1622. You can also fill out our contact form to schedule an appointment. We serve customers in Canton, GA, and the surrounding communities in Northern Atlanta.