Understanding the Energy Efficient Windows Rating in Canada

We live in a generally cool climate in this country. Canadians have had to deal with rising energy costs for decades now, ever since the 1970s.  The result has been an ongoing focus on energy efficiency – in other words, minimizing the amount of energy waste in almost all of our appliances, building products and systems, and vehicles.  For this discussion, we will focus on energy efficient windows for your home. 

Here’s what you should know about energy efficient windows in Canada. Read on.

What does the Term Energy Efficient Windows in Canada Mean?

The term energy efficient is used in many instances and many products in Canada – windows included.  There are variations, such as energy efficient windows, or energy saving windows, but they all mean basically the same thing: window assemblies that are designed to minimize energy escape from your home interior and also intrusion of unwanted heat or cold from the outside. The intent is to make it easier for you to keep your home cool in the hot summer months, and keep it warm in the harsh winter months.  The other major benefit is that energy efficient windows will save you money on your home heating and cooling costs.

The key to energy efficiency in windows is how they are constructed and insulated.  The standard for rating how well windows, doors and skylights perform, energy-wise, is ENERGY STAR®. 

ENERGY STAR Certification – What it Is

ENERGY STAR is a certification awarded to products which meet strict specifications and performance related to energy efficiency.  These products feature the ENERGY STAR sticker prominently displayed on them, so that as a consumer, you can be sure your purchase is a good one.  ENERGY STAR rated windows, for example, can perform up to 20% better than standard windows, in terms of energy consumption. That means they will allow less energy to escape from your home interior, and also that they will allow less unwanted cold or heat to enter your home.  A further designation – ENERGY STAR Most Efficient windows – can perform up to 55% better than standard windows – they are considered the best of the best.

What makes ENERGY STAR so important is that it provides a common platform and rating system for all window systems to be rated against.  They are evaluated in an independent laboratory, so you get an unbiased, apples-to-apples comparison when evaluating your next window purchase.  They also move with the times, so that if there are changes or innovations in the industry, they will be on top of it and provide reliable information on such changes.

Let’s take a look at some of the specific performance markers ENERGY STAR looks at with regard to window assemblies.

How ENERGY STAR Rates Windows

ENERGY STAR looks at a number of performance factors to give windows a rating with respect to their energy efficiency and performance.  The organization using these metrics is known as National Fenestration Rating Council. These include:

U-Factor or U-Value

These two synonymous terms – they can be used interchangeably – refer to how resistant a product is to heat loss.  It typically measures the performance of insulation, and it includes how window assemblies are insulated.  The lower the U-Factor, the better a window performs; a lower U-Factor means the window allows less heat escape or intrusion than a higher U-Factor rated product.  When you’re choosing new windows, compare their U-Factors – the lower the number, the better the window, in terms of resistance to heat loss.  U-Factor becomes especially significant in the colder months when your furnace has to work harder to keep your home warm and comfortable.

Solar Heat Gain Coefficient

We all love lots of natural light and sunshine coming into our home through our windows.  The downside of all that sun is that heat is also being transferred to your home interior. Solar Heat Gain Coefficient (SHGC) measures a window’s resistance to that heat transfer. It’s a number between zero and one (0 and 1) – the lower the number, the less solar heat transfer.

An important factor in limiting SHGC is the type of glass in the window assembly. Low-E glass, with its protective coating, does a good job of limiting solar heat transfer.  There may be instances, however, where solar heat transfer is actually desirable.  Discuss your specific needs with a qualified window installer to arrive at a suitable choice.

Visible Transmittance 

Visible transmittance (VT) is a measure of how much visible light passes through a window – a lower number indicates less light is making its way inside.  Low-E glass windows typically allow less light to pass, as they limit heat transfer at the same time.  The very best Low-E glass does allow plenty of light inside, however.

Air Leakage

This important measure shows how much air passes through the cracks in a window assembly.  The lower the rate of air leakage, the better. Keep in mind quality of installation also plays a role in overall air leakage in a window assembly.

R-Value

R-Value is the inverse of U-Value – it refers to a window assembly’s ability to retain heat.  When evaluating window performance, look for a low U-Value and a high R-value

Energy Rating

This is the overall score given to a window.  All the factors we’ve mentioned result in a total Energy Rating (ER) score of a particular assembly. Here in Canada, the climate zone plays a role in determining that rating.  ENERGY STAR rated windows in our country must achieve an ER rating of 25 for Zone 1, 29 for Zone 2 and 34 for Zone 3.

Some people may not be aware of the benefits of having energy efficient vinyl windows in Canada in their homes. But, there are many advantages that come with investing in these types of windows.

We hope you’ve found this summary of energy efficiency ratings for windows informative.  We welcome your questions and comments.