what are vinyl window ratings

What Are Vinyl Window Ratings?

Easy Steps to Understanding The Ratings of Your Vinyl Windows

Latest example of an NRFC vinyl windows ratings label

Example of an NRFC vinyl windows ratings label

Many of you will be wondering how to interpret vinyl window ratings that you see on a label. In fact some of you may not even know that there will usually be some form of displayed data on windows which you can make great use of.

Some time ago the The National Fenestration Rating Council (NFRC)was formed out of manufacturers, suppliers, builders, architects and designers, specifiers, code officials, utilities, and government agencies and they collectively devised a window energy rating system based on product performance (your vinyl window).

They came up with a series of ratings based on a number of critical measurements of a window that demonstrated it’s performance (or in fact, non-performance, if it was a badly designed window in terms of say energy-saving for example).



These vinyl window ratings look at:

  • U-Factor
  • Solar Heat Gain
  • Visible Transmittance
  • Air Leakage

On some more recent labels you may also find Condensation Resistance.

Let’s look at each of these and see how you can use them to determine the best windows for you as well as compare different brands/makes with each other.

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Vinyl Windows U-Factor

This is the most common rating used and measures the rate at which heat is lost through a material. The lower the U-value, the lower the amount of heat lost and the lower the amount of energy wasted. Most window ratings fall between 0.2 and 1.20. The lower the number, the better the window is. To achieve an Energy Star Rating (see below), a window must have a minimum U-Factor of 0.35. So you are looking for a window that ideally has a rating between 0.2 to 0.35.

Solar Heat Gain Coefficient

This factor (SHGC) measures the amount of solar heat that is transmitted through a window. This rating scale goes from 0 to 1. To prevent your rooms getting too hot, you’ll want a low SHGC figure. The lower the figure, the less heat is transmitted from outside into your rooms. That also means your air-conditioning or other cooling costs are reduced. A rating of 0.4 or less is recommended for warm areas.

Please note though that if you live in a cool area, you may want your SHGC rating to be higher in order to make use of free solar heating.

Visible Transmittance

This is simply a measure of how much daylight is transmitted through the window. It is a rating between 0 and 1 where 1 is the highest and effectively transmits 100% of the light (note that not even clear glass transmits 100% of the light falling on it, so don’t expect this value). A high VT rating is desirable to maximize the amount of light available in any room. Note that all coatings on glass, eg on low-e windows, will to some extent lower the VT rating.

Air Leakage

The Air Leakage rating (AL) is a measure of how much air literally leaks through cracks and crevices on the window construction. The rating number ranges from .1 to 1, but anything over .3 is considered a ‘fail’. The lower the AL rating, the less air will pass through the cracks.

Condensation Resistance

This is a measure of how well a product is able to resist the formation of condensation on the inside. It’s a relatively new measure and you may not see it on all window ratings labels just yet. If you do however, it is a rating that ranges from 0 to 100. The higher the rating, the better that window is at resisting condensation.

So there you have it, the fundamental vinyl window ratings and their meanings. These will allow you to make wise choices based upon your individual circumstances.

Energy Star®

Energy Star Label & Zones helping you find the best vinyl replacement windows

Energy Star Label

You may already be aware of Energy Star®. This is a government-backed program to encourage use of energy-efficient products throughout the commercial world, including windows. So you’ll often see an Energy Star label on the window announcing that it conforms to minimum standards to reduce energy-usage.

The Energy Star guidelines for windows are tailored to four climate zones. For example, windows in the North are optimized to reduce heat loss in the winter, while windows in the South are optimized to reduce heat gain during the summer. So Energy Star windows from one State may not be suitable for another.

The four climate regions with one recommended product designation for each are as follows:

Northern Climate Region Ratings

– Windows must have a U-factor rating of 0.35 or below

North/Central Climate Region Ratings

– Windows must have a U-factor rating of 0.40 or below
– With a Solar Heat Gain Coefficient (SHGC) of 0.55 or below.

South/Central Climate Region Ratings

– Windows must have a U-factor rating of 0.40 or below
– And an SHGC of 0.40 or below

Southern Climate Region Ratings

– Windows must have a U-factor rating of 0.65 or below
– And an SHGC of 0.40 or below

After considering the above you will know which are the best vinyl window ratings for your state and your personal circumstances! You can now confidently request your free quotes from up to 4 screened professional contractors and get what you know to be the best. Just click the following button for your free no-obligation quotes:


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