Understanding Your Window Performance

Understanding your window performance | Replacement Windows Denver | New Windows for America

It is important to understand the energy performance ratings of your windows and doors as it relates to their potential for gaining and losing heat. The National Fenestration Rating Council (NFRC) provides information enabling homeowners to accurately compare window performance. Here is a summary of what gets measured and why.


U-Factor measures how well a window is insulated and prevents heat from escaping. While the U-Factor can take any value, typically windows range from 0.20 to 1.20. The lower the U-Factor, the better the window insulates. The lower the U-factor, the greater the window’s resistance to heat flow and the better its insulating value. U-value measures the rate of heat transfer through glass (glazing). U-values, depending on climatic conditions.

Solar Heat Gain Coefficient

Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from sunlight. It can range in value from 0 to 1. The lower the Solar Heat Gain Coefficient, the lower the level of visible light that can affect the brightness of a room’s interior, and the less solar heat the window lets in. The sun can provide free heat in the winter, but lead to overheating in warmer conditions. Selecting different types of Low E glass coatings allows for balancing Solar Heat Gain appropriately for each individual home. Certain products use spectrally selective glass that blocks infrared light while still allowing high levels of visible light—so you can daylight your home while maintaining comfortable temperatures.


Visible Light External Reflectance or VLR refers to the percentage of visible light that is reflected externally by the glass as detected by the human eye. The higher the VLR, the lighter your windows allow in your home.

Air Leakage

Air leakage is a natural part of all operating windows. It is the rate of air movement around a window, door, or skylight in the presence of a specific pressure difference across it. The lower the number, the less air flows through the window when it is closed and locked.  Air leakage also depends on the proper installation of a window, which is assumed in all ratings.

Save Money, and Use Less Energy

Installing ENERGY-STAR® qualified windows and doors lowers energy bills and saves you money. Replacing old windows with ENERGY-STAR® certified windows lowers household energy bills by an average of 12 percent nationwide. Lower energy consumption also reduces greenhouse gas emissions from power plants and homes. Can you feel your carbon footprint shrinking?

Shop for Windows that Perform Best for Your House

Window orientation and window direction are important factors to enhance your savings and can increase the energy efficiency of your home, as well as make it more comfortable to live in. The orientation of the windows in your home can affect the lighting of the rooms resulting in electricity and heating consumption. For example, south-facing windows allow plenty of light into the room as the sun tracks mostly in the southern half of the sky. A north-facing window typically receives less natural light, so choosing the right size and high-performance glass can make a huge difference.

Ask the Team at New Windows for America about how our windows can be specified with high-performance glass to meet ENERGY-STAR® criteria for our specific climate zone here in Colorado.

Selecting the right window for your home | New Windows for America

Ready to Replace Your Windows?

Ensure your windows are as energy efficient as possible to help you save energy, reduce your heating and cooling costs, and overall improvement of your comfort in your home. New Windows for America offers all kinds of different windows and doors, including ENERGY-STAR® rated windows and doors! New Windows for America has 25+ years of experience with installing windows, doors, and siding for your entire home! We are happy to work with you on finding the best window replacement for your Colorado home and can offer you a free estimate.

Contact our New Windows for America Team today and get a free estimate.