How to Decode NFRC Labels on Replacement Windows

The fastest way to identify energy-efficient replacement windows for your next wood window replacement is by looking for ENERGY STAR® certification and National Fenestration Rating Council (NFRC) labels – the latter being those little white labels with values that represent U-factor, SHGC, and Visible Transmittance. If you’ve always wondered what these numbers mean, here is a quick guide.

The NFRC Label

Window and door glass must first be tested in laboratories approved by the National Fenestration Rating Council (NFRC) before the product receives an ENERGY STAR certification. The results are then recorded as values that you will find in every NFRC label. The following are the three required values:

  • U-factor – Also known as U-value, U-factor measures how well the product prevents heat loss and is represented as a value between 0.15 and 1.20. Lower U-values mean better heat retention. Some sales literature may indicate R-values along with U-factor. U-factor measures heat transfer rate, while R-value measures heat conduction – the lower the value, the less conductive the product is, and therefore less prone to heat loss.

  • Solar Heat Gain Coefficient (SHGC) – SHGC measures how efficient the product is at blocking solar heat, expressed as a number between 0 and 1. The lower the SHGC, the lesser solar heat that passes through.

  • Visible Transmittance (VT) – VT measures how much natural light comes through the product, and is also expressed as a number between 0 and 1. If you want a brighter room during the day, choose a wood window replacement with higher VT.

Other optional ratings include Air Leakage (AL), which measures how much outside air comes through the product, and Condensation Resistance (CR), which measures the product’s resistance to condensation.

What These Values Mean to You

Each home has its unique requirements, and sometimes even rooms in the same house have their own requirements. For instance, if you tend to be uncomfortable when it’s slightly cold, you may want a combination of low U-factor and medium to high SHGC. Or perhaps you have a home office, and you want to reduce daytime glare, in which case you should choose replacement windows with low VT. Knowing how to read these values can be helpful if a certain room has specific requirements.

Kroll Construction has been serving residents of Detroit, MI and nearby areas for over 50 years. Our consultants can help you find the exact kind of wood window replacement for your home. If you would like to know more about our services, call us today at (888) 338-6340 or fill out our contact form to schedule a free in-home consultation and estimate.

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