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Canada’s Window Energy Rating is Flawed: Here’s Why

| July 7, 2021

Canada’s Window Energy Rating Makes No Sense

Buying replacement windows is an expensive, highly involved process. With so much riding on the investment, you should be confident that you are getting the best possible information from both window companies and third-party resources. This is where Canada’s Window Energy Rating (ER) comes in. But is it information you can count on?

Developed by ENERGY STAR® in Canada as a way to gauge the energy performance of a window, the Energy Rating is a flawed metric that can cost homeowners thousands of dollars in energy bills over the lifespan of a window. While it sounds great at a high level, it distorts the information that many Canadian homeowners need to make correct decisions regarding energy efficiency and window replacement. Tellingly, it is not used anywhere else in the world as an indicator of energy-efficient windows.

So to help you understand Canada’s Window Energy Rating and why it’s flawed, we put together this guide. As always, we want to arm you with the right information to make the best purchase possible when the time comes for you to replace your windows.

Browse this content:

1. To Start, What is Canada’s Window Energy Rating?

2. Three Efficiency Metrics Used to Calculate Canada’s Window Energy Rating

3. How Do These Energy Efficiency Metrics Fit Into the Energy Rating Equation?

4. Why Placing So Much Emphasis on the Solar Heat Gain Coefficient is Flawed

5. Plugging in Real Energy Efficiency Metrics to the Energy Rating Equation

6. Shopping for New Windows? Look Beyond Canada’s Window Energy Rating

window energy rating

To Start, What is Canada’s Window Energy Rating?

According to the technical specifications of ENERGY STAR® certified residential windows, doors and skylights sold in Canada, the Energy Rating is defined as “a unitless value derived from a formula that balances heat loss (U-factor), air leakage loss and potential passive solar gain of a fenestration product.”

In other words? It’s a number that takes into account three key energy efficiency metrics in order to easily rate and grade a window’s energy efficiency. The ER grade is a single number — the higher the number, the more efficient the window. To achieve ENERGY STAR® certification and qualify for Canada’s Greener Homes Grant, a window’s ER must be 34 or higher. If a window achieves an ER of 40 or higher, it receives “most efficient” certification.

At a high level, this all sounds great; understanding a window’s energy efficiency is complicated and a rating system that seeks to simplify it for homeowners can be helpful, provided of course that the information is accurate.

Before we go any further, it’s important to have a firm understanding of what those key energy efficiency metrics are. This will make it easier to understand why Canada’s Window Energy Rating is flawed.

Three Efficiency Metrics Used to Calculate Canada’s Window Energy Rating

The metrics that form the basis of the ER are widely accepted. They are used by the National Fenestration Rating Council (NFRC) — an independent body that provides homeowners with reliable third-party information about energy-efficient windows.


U-factor determines the rate at which heat escapes through a window. The lower the U-factor number is, the better the window is at mitigating heat loss. The typical range to look for is between 0.20-1.20

Solar Heat Gain Coefficient (SHGC)

This metric determines how much solar heat enters a home via a window. The lower the number, the less heat enters. SHGC ranges between 0 and 1 and windows are generally between 0.25 and 0.8.

One key thing to note: A “good” or “bad” Solar Heat Gain Coefficient rating largely depends on the climate where the home is located. For example, homes in Northern Canada exposed to long winters and minimal warm weather would want a higher SHGC to take advantage of more solar heat gain. Conversely, a lower SHGC is essential in the Southwestern United States, where homes see ample sunshine year-round. Put simply, a lower SHGC can reduce cooling costs, while a higher SHGC can reduce heating costs.

Air Leakage

Air leakage infiltration measures the amount of airflow into the building via the window and exfiltration is the flow of air out of the building. The lower the number, the better your windows will be at preventing unwanted airflow. Ideally, you will find numbers that are ≤ 0.3.

window energy rating

How Do These Energy Efficiency Metrics Fit Into the Energy Rating Equation?

Now that we have an understanding of what metrics determine a window’s energy rating, let’s have a look at the equation itself. This is how the equation appears on the Government of Canada’s webpage on the technical specifications for windows, doors, and skylights:

ER = (57.76 × SHGCW) – (21.90 × UW) – (1.97 × L75) + 40

Even a mildly discerning look at this equation can tell us how heavily the ER weighs certain variables in comparison to others. Let’s break the equation down further:

(57.76 × SHGCW)

This first part tells us that the Solar Heat Gain Coefficient is weighted the most heavily in the Energy Rating equation. Measured in watts, the SHGC number for a window is multiplied by 57.76 to secure the first value. This is perplexing, considering that there is no one-size-fits-all value for SHGC that fits every situation. Plus, SHGC is the metric that is most easily adjusted through Low-E glass formulations, but more on that later.

(21.90 × UW)

This second part concerns U-Factor. To reiterate, U-Factor measures how well a window can keep heat from escaping from the inside of a room. Considered to be the most crucial energy efficiency metric by the broader fenestration industry, it is telling that Canada’s window Energy Rating equation places less than half (21.90) the amount of emphasis it places on the SHGC.

(1.97 × L75)

Finally, this part of the equation concerns Air Leakage. Another essential component of an energy-efficient window, the Air Leakage rate (in this case at a pressure difference of 75 pascals) has the least amount of weight in the equation (1.97).


A constant of 40 ensures that the ER values are positive.

Why Placing So Much Emphasis on the Solar Heat Gain Coefficient is Flawed

Recall that a window’s Solar Heat Gain Coefficient measures how much solar heat enters the home via the window. This is undeniably an important metric when it comes to gauging a window’s energy efficiency. However, context matters greatly here:

First, a “good” or a “bad” SHGC can change depending on where you live — a lower SHGC is great for hot climates with ample sunlight; a higher SHGC can be beneficial for colder, northern climates who want to take advantage of as much radiant heat from the sun as possible.

Second, a window’s SHGC boils down to the glass package and has very little to do with the quality of the window’s construction. These glass packages come fitted with Low-Emissivity (Low-E) coatings which allow for easy adjustment of the SHGC. Plus, considering that most window companies purchase these glass packages readymade, achieving a high SHGC is not something these companies should be hanging their hat on.

What is Low-E Coating?

This transparent, incredibly thin coating helps to regulate the solar heat that comes through a window, allowing spaces to cool more efficiently in warmer temperatures. It is key in determining a window’s SHGC.

The key point here? Low-E coating is effective because it’s tailored to deliver the right SHGC rating for specific climate regions. In warmer climates, for instance, the glass can be formulated with a heavy Low-E coating such as Guardian’s Sunguard 62/27 that will significantly reduce the amount of heat coming through the glass. This will produce a much lower SHGC. In Southern Ontario, where the weather changes drastically from hot to cold over the year, a balanced Low-E formula such as the ClimaGuard 70/36 is best. It’s designed to allow you to take advantage of the sun’s heat in the winter, while not having it be overwhelming in the summer months.

window energy rating

With Canada’s Window Energy Rating, a Higher SHGC Will Always be Favoured. That’s a Problem.

We can now begin to see the problem. By weighting the SHGC so heavily in the ER equation, the Government is essentially telling both window companies and consumers that the higher they can get their SHGC number, the better.

But this is flawed! While a very high SHGC number is great for those living in Northern Ontario or Manitoba, where the winters are often longer, darker and colder, it won’t be nearly as beneficial for even those living in Southern Ontario, where summers can be very long and hot.

In hot, humid summers in places like the GTA, a window with a high SHGC will lead to unwanted and unnecessary heat transfer into the home. This type of glass makes homes extremely uncomfortable during the summer and will make consumers spend a lot of money cooling their homes. As any homeowner knows, A/C costs are significantly higher than the costs associated with heating a home during the winter.

To drive this point home even further, let’s see the energy rating equation in practice. 

Plugging in Real Energy Efficiency Metrics to the Window Energy Rating Equation

To see the flaws in Canada’s Window Energy Rating, let’s compare two window products and plug their real values into the equation.

Window #1: The Magic™ Casement Window
Window #2: A Competitor (Rated “Most Efficient” due to its Energy Rating)

The Magic Casement Window

Solar Heat Gain Coefficient: 0.22
Low-E Glass Package: Guardian 70/36 (balances SHGC for climates that have hot summers and cold winters)
U-Factor: 1.08
Air Leakage: 0.1

ER = (57.76 × 0.22) – (21.90 × 1.08) – (1.97 × 0.1) + 40
ER = 29

Despite having a solid U-Factor value, an extremely low Air Leakage value, and an SHGC that works in climates with hot summers and cold winters, the Energy Rating of the product is low. Why? Because it’s concerned with creating a balanced product instead of simply maximizing the SHGC value.

The Competitor’s Casement Window

Solar Heat Gain Coefficient: 0.53
U-Factor: 1.31
Air Leakage: 0.2

ER = (57.76 × 0.53) – (21.90 × 1.31) – (1.97 × 0.2) + 40
ER = 42

With a U-Factor that falls outside the NFRC’s recommended range of 0.20-1.20, this competitor’s casement window is said to be more efficient than the Magic Casement Window. Why? Because of the incredibly high SHGC value of .53.

Just for a second, think of both of these windows installed on the same house in Southern Ontario. On a scorching hot summer day, think of how much more heat from the sun would be beaming through the competitor’s window. Think of how much harder an A/C unit would have to work to offset the heat coming through that window. Without lowering temperature setpoints on the thermostat, the home would almost certainly be sweltering during the day!

Considering the costs associated with cooling your home in the summer, in what world is this arrangement more efficient? Only in one that puts stock in the Energy Rating.

cottage windows

Shopping for New Windows? Don’t Rely On Canada’s Window Energy Rating

When it comes to finding energy-efficient replacement windows in the GTA and beyond, it is important to take third-party certifications into consideration. Metrics like Solar Heat Gain Coefficient, U-Factor, and Air Leakage matter a great deal and are key in gauging a window’s overall energy efficiency capabilities — there’s a reason third-party organizations like the NFRC and ENERGY STAR® use them. However, when used in the context of Canada’s Window Energy Rating, it’s far too easy for homeowners to misinterpret them.

From the frames and glass to construction and installation, there is a lot that goes into making your replacement windows energy efficient. Ultimately, what matters most is ensuring that your replacement windows have the right metrics for your home. This is far more important than simply achieving a high SHGC value, which is what the Energy Rating would have many consumers and window companies believe.

For all these reasons and more, we formulate our own glass units to meet specific solar and energy-control needs of different regions and climates. There are a variety of customizable options including glass types, gas fills, glazings, and coatings. The customization of our glass units allows us to maximize your windows’ performance in accordance to your specific preferences, climate, and home’s construction.


Learn more about window replacement on our blog!

1. Canada Greener Homes Grant: Upgrade to Energy Efficient Windows

2. The Benefits of Retractable Window Screens and Blinds

3. 6 Ways to Tell if You Need to Repair of Replace Windows

4. Why Crank Operated Casement Windows are Mechanically Flawed

5. 4 Stunning Panoramic Window Walls

6. The Main Issue With Hollow Vinyl Replacement Windows

7. 3 Factors That Lead to Secure, Durable and Efficient Replacement Windows


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