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How to Read a Window Energy Performance Label


When buying new windows, comparing styles, sizes, and colors isn’t the only way to find the best product for your home. The National Fenestration Rating Council (NFRC) has made comparing windows easier with the NFRC energy performance label. It is a window sticker that tells homeowners a lot about the product’s efficiency ratings, based on an established testing and certification process.

This window label, which customers may or may not find easy to remove, tells you a window’s:


The U-value (or U-factor) indicated on the middle-left of the label, below the NFRC logo and product details, is part of the “Energy Performance Ratings”. It is a measurement of the window’s rate of heat transfer. Ranging from 0.20 to 1.20 (a triple-paned window may be even lower), it tells you how effective a window is at preventing heat loss from a building. The lower the number, the better the window is at retaining heat, so you can save money on heating costs.

Solar Heat Gain Coefficient (SHGC)

The SHGC is indicated to the right of the U-value. It measures resistance to heat entry and the amount of solar radiation allowed in comparison to how much is blocked. With lower values, you can see more savings on air conditioning (numbers range from 0 to 1). However, a low value isn’t the only thing to consider. The directional orientation of the window affects how much sunlight it’s exposed to, so a low SHGC may be effective in summer and a higher SHGC for south-facing windows in winter may contribute to more efficient heating.

Visible Transmittance

Listed under “Additional Performance Ratings”, visible transmittance ranges from 0 to 1 and describes how much daylight is allowed in. The higher the rating, the more natural light your home will receive, which is more efficient than using artificial lighting. Lower scores don’t always mean the window is less energy efficient, especially with triple-pane types.

Other Ratings

The NFRC label also comes with some optional ratings. These can include air leakage (0.1 to 0.3), which at lower numbers means fewer drafts, and a condensation rating (0 to 100) that tells how good the window is at resisting moisture condensation.

The Difference Between ENERGY STAR and NFRC Labels

An NFRC label provides specific details on a window’s performance. It incorporates several categories, while the ENERGY STAR label’s primary purpose is to designate a product as energy efficient. However, installing ENERGY STAR windows can have many benefits, including improved insulation, efficiency, and long-term cost-savings. This label is part of a U.S. Department of Energy program that promotes energy efficiency via products and devices that reduce consumption.

The two labels also look very different. You’ll notice the prominent ENERGY STAR logo as well as the EnergyGuide label that identifies an “Estimated Yearly Operating Cost”. It can also recommend a product for specific climate zones.

Find High-Quality Windows at Window World of Boston

Window World of Boston specializes in energy efficient windows, including those with SolarZone™ insulating glass and the Warm-Edge Spacer System, as well as efficient doors. We help with the entire process of buying windows and help find the best products and options for your house, climate, and budget. Open for business during the COVID-19 pandemic, we are taking safety measures including temperature checks for employees, social distancing during window installation, and wearing masks, gloves, and other protective clothing.

Our adjusted hours are as follows:

Tuesday 10AM–2PM
Wednesday 10AM–2PM
Thursday 10AM–2PM
Friday 10AM–2PM
Saturday Closed
Sunday Closed
Monday 10AM–2PM

Request a free estimate online or call our Woburn office at 781-262-3925 for more information.

Services We Offer
Window World of Boston has an A+ BBB Rating and offers industry-leading solutions for replacement windows, doors, siding and more. We follow through every job from start to completion while our friendly, knowledgeable staff is there to answer your questions and provide any level of customer support you need. Window World is committed to providing the highest customer satisfaction.
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