A Guide to Window Efficiency Ratings

A Guide to Window Efficiency Ratings

What is ENERGY STAR Certification and how are these ratings determined?

There are many things to consider when completing a renovation or upgrade as a homeowner, energy efficiency should be one of the top considerations. There are many benefits of utilizing energy-efficient replacement materials, such as replacement windows and replacement doors but the financial benefits are usually what stands out the most. Saving energy, means saving money on energy bills. 

If you are considering a window replacement project for your home, below we share a window efficiency ratings outline.

How is Window Efficiency Measured?

In agreement with the U.S. Environmental Protection Agency (EPA), Natural Resources Canada (NRCan) has come to promote the use of ENERGY STAR Certification. This partnership with the Government of Canada ensures there are high-efficiency products available on the market, and that they are easily identified. To be granted certification, new products must be approved by third-party labs, which assess their performance.

Windows, doors, and even skylights are tested by accredited laboratories against industry standards, and the results are then verified further by a third party. Each product prototype is put through rigorous testing and simulations to test for qualities such as temperature resistance, insulation, air and water tightness, noise reduction, and more. To receive certification, these products must be tested by one of the following accredited laboratories:

  • CSA International (CSA)
  • Intertek Testing Services (ITS)
  • Labtest Certifications
  • Quality Auditing Institute Ltd. (QAI)
  • The National Fenestration Rating Council (NFRC)
  • Keystone Certifications, Inc.

ENERGY STAR Certification

To qualify for certification, windows, doors, and skylight products must meet many different criteria. A select few meet the criteria, setting a high standard of efficiency among the market. In fact, only a very small number of products exceed this benchmark, which are then awarded the ENERGY STAR Most Efficient classification, the highest possible energy efficiency rating. In Canada, energy efficiency is determined by assessing the following metrics:


Also known as the U-Value, this measures the amount of heat that is transferred from a warm side of a window or door to the cold side.  Products with a lower U-Value will transfer heat slower, making them more efficient and lead to additional cost-savings. Less heat will be lost during colder months and less heat will enter the home during warmer months. It’s important to remember there are two different scales of measurement used; metric and imperial, which are expressed differently. 

Like other forms of measurement, U-Factor measured in imperial and metric systems have different values. The metric U-factor, which is internationally used, is expressed as W/m²K. The metric system will have a larger value than imperial, so it’s particularly important to be aware of which form of measurement is being used when comparing products and standards.

Solar Heat Gain Coefficient (SHGC)

This metric is used to determine how much solar heat is transmitted through a window into a home. Measured on a scale of 0 to 1, a lower rating indicates that a lower amount of solar heat is transmitted. The benefits of this rating can be viewed either way, however.

Different types of glass and coatings are used to help reduce the amount of solar heat gain, which is great in warmer climates. Reducing the amount of heat conducted from solar energy can lower homeowners cooling costs tremendously. In turn, homes located in areas with cooler climates may value a higher SHGC rating, as more solar heat can help reduce heating costs.

Air Leakage

This rating is significant when selecting an energy-efficient window or door. Measured by the CSA 440 standard, products can be rated A1, least airtight, to A3 most airtight. The less airtight a window or door is, the more energy is lost to the outdoors. Whether you’re heating or cooling, air leakage reduces energy efficiency and can result in higher expenses. It’s best to choose a product with a higher air leakage rating.

Energy Rating (ER)

Taking other metrics into account, the energy rating provides a more accurate way of comparing the energy efficiency of different products. Considering a product’s U-Factor, SHFC, and air leakage, the Canadian Energy Rating offers a more thorough measurement for comparison. An ER rating is illustrated with a numerical value, which at one time was a range. 

Before 2020, different zones were designated across the country, which had varying minimum energy ratings depending on specific standards. Changes have since been made to this ENERGY STAR metric, however. Now, there is a minimum standard rating of ER 40 (metric) across Canada for ENERGY STAR Certified windows and doors.


Although this metric is not tested against performance standards, it is often referred to in the industry by contractors. R-value is similar to U-Value, as it reflects the same process – the amount of heat transmitted through a window. However, R-Value represents the windows’ ability to retain heat, rather than the amount of heat lost. An energy-efficient window or door should have a higher R-Value, but a lower U-Value.

Visible Transmittance (VT)

This metric is indicated by a percentage and refers to the amount of light that can pass through a window. A lower value means the window allows less natural light to shine through, which is a result of the material used. As mentioned previously, coatings can be used on glass to reduce the solar heat gain of a product, which can also result in less light transmittance. 

What Are The Benefits of Energy-Efficient Windows?

  • Save money!

Choosing ENERGY STAR-certified windows, doors, and skylights helps to reduce your home’s energy consumption in several ways which leads to reduced heating and cooling costs.

  • Stay comfortable

By installing high-rated products, overheated rooms and cold drafts can be avoided, limiting the amount of energy required to make your living spaces comfortable. Having a consistently comfortable home throughout is just another major benefit of energy-efficient replacement windows and doors. 

  • Peace of mind

Investing in windows, doors, and skylights is an important and at times costly decision. You can enjoy peace of mind when your replacement windows and doors are qualified to perform as anticipated with ENERGY STAR Certification.

Most Current Updates

Before diving into a new window replacement project, it’s important to be aware of the current ENERGY STAR ratings. For instance, there were major changes to the Energy Rating metric, which at one time varied depending on specific climate zones.

What Are ENERGY STAR Climate Zones?

Canada is the second-largest country in the world and embraces a wide range of climates. Previously, there were different zones allocated across the country, each with its own minimum Energy Rating and/or U-Factor requirements. Up until 2015, there were four Climate Zones – A, B, C and D, from warmest to coldest. This system became confusing to homeowners who would mistakenly purchase products that were not sufficiently rated for their climate zone.

This standard has since been updated with one benchmark across all of Canada, making the process much easier for consumers. As of January 2020, any window, door, or skylight product must have a minimum Energy Rating (ER) of 40 or U-Factor of less than 1.05 W/m2·K to be ENERGY STAR Certified. Rated against the coldest climates in the country, consumers can rest assured that any certified product they choose will be energy-efficient and keep them warm!