Want to boost your home’s energy efficiency? Replacing your windows is one of the most effective upgrades you can make to your home. But how can you tell if your current windows are holding you back? In this guide, we’ll break down everything you need to know about window energy performance, from how efficiency is measured to the common window issues that could be costing you.
How Window Energy Performance is Measured
Before moving forward with a window replacement, it’s important to understand precisely what is considered when rating a window for energy efficiency. The two main ratings to look for on both your current and potential replacement windows come from ENERGY STAR and the National Fenestration Rating Council (NFRC). Here is what they measure to determine the energy efficiency of windows and doors.
Heat Gain and Loss
Windows lose and gain heat as it transfers from the exterior through panes and framing and other forms of both solar and non-solar heat flow. These energy performance characteristics, influenced by outside temperatures, are measured through a window’s U-Factor and Solar Heat Gain Coefficient (SHGC).
- U-Factor essentially measures a window’s insulative quality. Ranging from 0.20 to 1.20, a lower U-Factor means the window allows less heat to penetrate into the home.
- Solar Heat Gain Coefficient (SHGC) measures how well the insulated glass resists or blocks heat gained by the sun (solar heat flow). This measurement is more complex, as in some climates, you may want a higher SHGC, which is better for passive solar design during the winter months. Ranging from 0 to 1, lower numbers indicate greater resistance.
Sunlight Transmittance
Sunlight transmittance is the amount of sunlight that enters the home through a window’s glass and glazing, transmitting solar heat as the sunlight is absorbed into surfaces in the home. Sunlight transmittance is measured with two factors:
- Visible Transmittance (VT) measures the amount of visible light penetrating through a window, measuring from 0 to 1 with higher transmitting more visible light.
- Light-to-Solar Gain (LSG) is the ratio of VT to SHGC and is used to indicate the relative efficiency of how much a window allows in sunlight versus the amount of heat it blocks. A higher LSG means more light is being transmitted without letting in too much heat, providing ample natural light without excessive heat gain.
Air Leakage
While most windows may have some amount of air infiltration, this can be worsened by having drafty windows without a proper seal. Air leakage can significantly affect ambient temperatures in your home, making your heating and cooling system work overtime to balance out the cold or heat emanating from outside. The lower your home’s air leakage rating, the better.
UV and Infrared Radiation
UV and infrared radiation bring heat into the home through windows if the harmful rays aren’t blocked with Low E window glass or other treatments. While infrared rays produce heat, UV rays both bring heat into the home and can cause damage or fading to flooring and furniture over time. The lower your windows’ UV or infrared radiation percentage, the better.
Determining Best Ratings for Window Replacement
Different climates naturally have different needs for energy efficiency ratings on windows. To help homeowners determine the best ratings for their area prior to window replacement, ENERGY STAR divides the United States into four climate zones, updated as of October 2023. Each region has recommended ratings for U-Factor and SHGC, which homeowners can compare to the ratings for replacement windows before purchasing.
How Rolox Windows Measure Up
The Kansas City area is in the North Central climate zone. This means homeowners in our area should look for windows with a U-Factor of 0.25 or less and an SHGC of 0.40 or less. So, how do Rolox windows measure up? Our windows average a U-Factor of 0.22 and an SHGC of 0.21, putting them well below the maximum for the ENERGY STAR seal of approval!
Ready to Give Your Energy Efficiency a Boost?
There are many benefits to replacing your windows with new, energy-efficient windows. Not only is it better for the environment, but it’s better for your pocketbook, thanks to the noticeably lower energy bills! If your windows aren’t meeting the standards for energy performance, contact Rolox Home Service today to learn how our best-in-class windows can make a difference.
