A Beginner’s Guide to Energy Efficient Windows

energy efficient windows

When it comes time to replace your home’s windows, there’s no such thing as a one-size fits all market, especially in terms of energy efficiency windows. But a window’s projected energy performance isn’t as easy to figure out as you might expect. With these helpful tips, you’ll be able to read a window energy efficiency label and choose the window that will be a perfect fit for your family.

Energy Star and National Fenestration Rating Council

Each window will come with two labels: a blue-and-yellow Energy Star label and a white National Fenestration Rating Council (NFRC) label. NFRC is a nonprofit that reports the crude data about how well a window will perform, whereas Energy Star will give you a peek into which windows are the pinnacle of energy efficiency. Only those that meet the strict guidelines placed by the Department of Energy will be certified as Energy Star compatible.

Energy Performance Measurements:


The U-factor rating measures the rate at which heat is lost through the fenestration, with lower U-values indicating better insulation. Energy Star approved windows will have a U-value less than or equal to 0.3, though the U-value measurement can go as high as 1.2.

Solar Heat Gain Coefficient

Blocking the sun’s solar radiation and heat  is another important job for energy efficient windows, and the Solar Heat Gain Coefficient (SHGC) evaluates how effectively a window is able to do just that. In general, the lower SHGC rating, the more efficient the window will be—though that isn’t a hard-and-fast rule, and homeowners should look for a rating of 0.3 or less.

energy efficient windows

Additional Measurements:

Visible Transmittance

As the name implies, visible transmittance (VT) gauges the amount of visible light that is permitted to pass through the window. It used to be that light and heat went hand in hand, but modern glazing technologies have changed that experience. VT is rated from 0 to 1, with a higher VT indicating that more light is transmitted.

Air Leakages

Evaluated as the cubic feet of air that is able to pass through a square foot of window, air leakage ratings may or may not be included in a window’s statistics. Energy Star doesn’t take air leakages into account since window construction materials are subject to alter over time and subsequently cannot be measured precisely. Though the standard building code rating is .03, the lower the figure, the less air is able to seep through your energy efficient windows

Condensation Resistance

With a range of 1 to 100, condensation resistance (CR) calculates how much moisture is able to collect on the interior of the window and between glazing layers. Most Energy Star-approved windows are already built to withstand moisture, so they will generally come with higher CR rating already.

Now that you understand the ins and outs of energy efficiency window ratings, take the time to compare various options and talk to a professional who can help walk you through exactly which window will best serve your home.

Leave a Reply