How to Read a Window Label

Jul 20 2022 Posted By Ontario Window Reviews

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A row of windows and a close-up of the NFRC window label

Aside from aesthetics and ease of use, durability and energy efficiency are important factors to consider when getting replacement windows. Luckily, all of the information you need is right on the window label. 

But if you’ve gone window shopping recently, you may have noticed that there are plenty of technical terms found on window labels. You might see the Energy Star icon—which means the window helps you save energy—but what do solar heat gain coefficient, U-factor, and all those other metrics mean? 

This guide will help you figure out how to read the common components that usually appear on a window label. The next time you go window shopping, you’ll be able to have one look at those specs and understand whether or not a certain type of window is a good addition to your home. 

Let’s get started!

New windows getting window labels attached


The Importance of Knowing How to Read a Window Label

Typically, window labels with energy performance metrics come from third-party entities that have inspected the window. If a window passes certain standards for energy efficiency, it will usually also have the Energy Star icon on its label.

However, not all energy-efficient windows are equal. Some have better insulation or better protection from solar radiation. If you want to know how to read a window label, understanding what the numbers mean and knowing what a good range looks like is essential. 

Aside from energy ratings, window labels also carry critical information about the product, such as the following: 

  • The manufacturer
  • The material
  • The type of window
  • The presence of double or triple glazing
  • The presence of Low-E coating

What Are the Different Kinds of Window Labels in Canada?

In Canada, most window labels are from the Canadian Standards Association or the CSA Group. This is a global standards development organization that is dedicated to sustainability and social good. Other window labels may be certified by the National Fenestration Rating Council (NFRC). This is a US-based, independent, non-profit organization that specializes in establishing performance ratings for fenestration products. 

Apart from CSA and NFRC labels, windows in Canada can also be certified by the following accredited agencies, which are listed in Natural Resources Canada:

How to Read General Information on Window Labels


1. The Manufacturer

Make sure that you are buying your windows from a trusted window manufacturer known for creating high-quality, durable, and energy-efficient windows. Look through customer ratings and try to find out how long the company has been around. 

Aside from ascertaining quality, choosing a trusted and established manufacturer will also give you assurance regarding warranty. A window’s warranty is only as good as the capacity of the manufacturer to honour it. 

2. The Material

Consider the pros and cons of each window material so that you can get the best type for your home or property. Different window materials have varying strengths and weaknesses.

For instance, wooden frames are a classic choice but require constant maintenance. Vinyl windows require minimal maintenance and are great for insulation, but are not as easy to paint. Aluminum windows are durable but are prone to moisture damage and corrosion. 

3. The Type of Window

Next up in this guide on how to read a window label is considering the type of window itself. This is important for both aesthetic and functional reasons. Each type of window has pros and cons, as we’ve discussed thoroughly in our article, “7 Replacement Window Styles: Pros and Cons.

4. The Presence of Double Glazing & Low-E Coating

Multi-glazed windows are best for Canada’s harsh climate because they provide far better insulation than single-glazed windows. In some regions like Ontario, residential homes are required to have at least double-glazed windows with a low emissivity (Low-E) coating. A Low-E coating on windows is an invisible layer of metallic atoms that reduce harmful UV and infrared rays from the sun.   

Close-up of a double-glazed window cross-section, which is one of the key features indicated in window labels


How to Read a Window Label to Assess Energy-Efficiency

So far in this guide on how to read a window label, we’ve only talked about the general information that usually appears at the top-most part of the label. Now that we’re moving on to energy efficiency metrics, it’s about to get technical!

Let’s start things off with a quick cheat sheet for the different energy performance ratings: 

Energy Performance Metric: Better When It is… How It’s Reported
U-Factor Lower The possible range for windows is 0.20 to 1.20
Solar Heat Gain Coefficient Depends on Preference The scale is from 0.00 to 1.00
Energy Rating Higher The scale is from 0 to 50
Visible Transmittance Depends on Preference The scale is from 0 to 1
Air Leakage Lower The scale is from 0.1 to 0.3
Condensation Resistance Higher The scale is from 1 to 100

Now let’s go over these ratings one by one:

1. U-Factor

This factor measures the rate of non-solar heat transfer. This rate of transfer affects the window’s capacity to insulate. Therefore, the lower the U-factor, the better the insulation the window can provide. 

2. Solar Heat Gain Coefficient

Solar heat gain coefficient, also known as SHGC, represents the fraction of solar radiation that can pass through the window. A good SHGC value depends on your needs and preferences. 

  • Lower SHGC = cooler spaces during the summer (because minimal solar radiation gets through)
  • Higher SHGC = warmer spaces during winter (because solar radiation is maximized)

Because ideal SHGC values depend on seasonal needs, some property owners choose a range that’s in the middle. 

3. Energy Rating

This metric sums up three other important metrics: U-factor, SHGC, and air leakage. The higher the energy rating is, the more energy-efficient the window will be. 

4. Visible Transmittance

On window labels, visible transmittance is the amount of visible light from the sun that is allowed to pass through. An ideal value for visible transmittance depends on your needs and preferences. 

  • Lower visible transmittance = helps to reduce glare (because less visible light is allowed through)
  • Higher visible transmittance = helps to create a brighter space (because more visible light is let through)

5. Air Leakage

The air leakage value represents how tightly sealed the window is. The lower the air leakage, the more energy-efficient the window is. Aside from getting a window with low air leakage, it’s important to get your windows professionally installed so that air leakage is also minimized around the frame. Some window manufacturers offer professional installation to ensure this. 

6. Condensation Resistance

This value correlates to the likelihood of condensation forming on the interior surface of the windows. The higher the condensation resistance, the more insulated the window is. Therefore, higher condensation resistance values are preferred. 

Choose Windows from Trusted Companies

That concludes our guide on how to read a window label. The next time you see window labels, you’ll be able to understand the significance of each part—and you’ll be able to invest in the best windows for your property. 

Take the first step to getting reliable windows by referring to this list of trusted window companies in Ontario.

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