Window Labels: What You Need to Know

Energy Performance Labels: What You Need To Know

I know you’ve seen those weird blue window labels that just get peeled off with no thought.  Those window labels give important information and things you need to know! If you’re building a new home or remodeling your existing one, sooner or later you’ll probably need to go window shopping. With the myriad window styles and models available, this can feel a bit overwhelming. With expert help at Glassworks, we’ve discovered what you need to know about those energy performance labels.

Whether as a starting point in window selection or to help you choose between models, energy performance is a useful standard for narrowing down your choices. On average, a home loses 30% of its heating and cooling energy through its windows, so even a small difference in energy efficiency can make a big difference to your budget over time.

Our brick&batten designers spend a lot of time looking at houses that need new windows.  Choosing energy efficient windows is a no brainier and something that will not only help your curb appeal but also your wallet!

So, how do you select the most energy-efficient windows?

Just look for energy performance labels. To interpret these labels, it’s important to understand the intention behind each.

Here’s a simple explanation:


The blue ENERGY STAR®  label designates windows that have been certified as energy-efficient by ENERGY STAR®, a program sponsored by the U.S. Environmental Protection Agency and Department of Energy to promote energy efficiency. 

National Fenestration Rating Council (NFRC) label

The NFRC label displays four or five energy performance ratings results, each expressed as a number. These tell you how well the window, door, or skylight can be expected to perform in various categories of energy efficiency.

In short, the ENERGY STAR® label provides an at-a-glance way to determine whether or not a window qualifies as energy efficient. The NRFC label can help you make an apples-to-apples performance comparison between different brands, styles and models of window.

Understanding NFRC Energy Performance Labels

So, what exactly do the numbers and ratings on the NRFC label mean? 


The U-Factor is found in the upper left quadrant of the numbers portion of the label. It rates heat loss from a window or how how well the window insulates. These values will typically range from 0.25 to 1.25. Look for lower U-Factor numbers to minimize heat loss.

Solar Heat Gain Coefficient (SHGC)

The SHGC is located in the upper right quadrant of the NRFC label. This number indicates how efficient the window is at keeping out heat from the sun. SHGC numbers range from 0 to 1, with values of 0.25 to 0.8 being typical. The lower the number, the less heat will be admitted through the window. Look for a low number if you’re interested in passive solar heating. But if you want to limit summer heat gain to reduce air conditioning costs, you’ll want a high one.

Visible Transmittance (VT)

Under the U-Factor rating you will find another number ranging from 0 to 1. The VT number indicates how much light the window admits. If you want to lower lighting costs by taking advantage of natural daylight, look for a high number in this category.

Air Leakage (AL)

In the lower right corner of the label you will find the AL number, which measures the rate at which air passes though the joints in the window. This will be expressed as a number between 0 and 1, but NRFC ratings are typically between 0.1 and 0.3. The lower the number, the more air-tight (and energy efficient) the window will be.

Condensation Resistance

This rating is optional but, if included, it will be in the extreme lower left of the NRFC label. Scored on a scale of 1 to 100, this rating tells you how well the window resists water buildup. Higher scores indicate a more resistant window.

Overall, by using ENERGY STAR® and NFRC labels and the attached infographic, you’ll gain confidence in the window-selection process and be able to quickly zero in on the best choice for your home. Enjoy your window shopping!

Your home is your greatest investment, so making thoughtful choices about window selection, paint colors, lighting, awnings, etc. is important. We would love to partner with you on a virtual exterior design, giving you the confidence to move forward on your home exterior project. Get started today.

Author bio: Chuck Bosley is General Manager at Illinois Glassworks, LLC, a leading custom glass company serving commercial and residential customers in Chicagoland.