How To Use NFRC Factors To Compare Energy and Comfort Performance Of Window And Patio Door Brands

If you're going to purchase replacement windows and patio doors its very important that any window or patio door you consider be certified by the National Fenestration Rating Council (NFRC).  There a two reasons why.

First, A window or patio door cannot qualify for the ridged quality and energy and comfort performance requirements of the Federal Government's  Energy Star® certification if it has not been tested by an approved independent laboratory and the results certified by the NFRC.

Second. The NFRC label is attached to each window when it is manufactured. This NFRC data, represented in "Factors,"  provides you with a concrete way to compare the energy and comfort performance of the windows and patio doors on each proposal you receive for your project.

So you should use the NFRC performance factors as one of the important criteria in your choice of the windows and patio doors for your replacement window and patio door project.

If a contractor or window retailer cannot provide you with the NFRC performance factors for the product(s) they are proposing you purchase, and explain their significance, ... RUN!

We at Jantek Windows publish the NFRC Factors for all of our window and patio door models on the product pages of our website  but we want to give a quick guide to understanding what the NFRC factors on the NFRC Label mean.  Here we go!

By your understanding the NFRC energy performance factors it can help you determine how well a product will perform the functions of helping to cool your home or building in the summer, warm your building in the winter, keep out wind, and resist condensation. 

NFRC adopted a new energy performance label in 2005. It lists the manufacturer, describes the product, provides a source for additional information, and includes ratings for one or more energy performance characteristics. 

So now lets take a look at the NFRC performance Factors and understand what each signifies.


U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-value, the greater a window's resistance to heat flow and the better its insulating value. A lower U-Factor keeps your building warmer in the winter and cooler in the summer. 

Solar Heat Gain Coefficient

Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window (both directly transmitted and absorbed) and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits in the house. In colder climates you want a SHGC factor somewhere in the "mid  .20's" since you have a longer heating season. In the warmer climates, you want to see an SHGC in "High Teens" since you have a longer cooling season. 

Visible Transmittance

Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.

Air Leakage*

Air Leakage (AL) is indicated by an air leakage rating expressed as the equivalent cubic feet of air passing through a square foot of window area (cfm/sq ft). Heat loss and gain occur by infiltration through cracks in the window assembly. The lower the AL, the less air will pass through cracks in the window assembly.

Condensation Resistance*

Condensation Resistance (CR) measures the ability of a product to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. While this rating cannot predict condensation, it can provide a credible method of comparing the potential of various products for condensation formation. CR is expressed as a number between 0 and 100.

* This rating is optional and manufacturers can choose not to include it in testing or on the label.

So now you have a better understanding of how to use the NFRC Factors and Label to compare the energy and comfort performance of replacement window and patio doors. This is just one piece of the total picture but it is a very important criteria in your up front research to selecting the best replacement windows and patio doors for your project. We will address more of the pieces in our upcoming articles on energy performance, warranty, lead times, what to expect during installation, replacement window design etc. In the meantime if you would like to discuss more of your questions with our replacement window experts, or would like to have a quick no hassle Free TeleEstimate/Virtual Estimate on Vinyl replacement windows and patio doors, give us a call at (609) 564-1030 and we will be happy to help.

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