Understanding Energy Efficiency Ratings

Understanding Energy Efficiency Ratings
February 15, 2019 Windows 0 Comments

Understanding Energy Efficiency Ratings

When buying or replacing windows, you should always mind energy efficiency. Doing this without the help of an expert can be difficult. The first step in choosing the most energy efficient windows for your home is learning all of the important markers which give information about window performance and efficiency.

Energy Star

Energy Star is a symbol that stands for guaranteed energy efficiency for insulation products like doors and windows. It is a system developed and used in Canada and the US. Having an energy star on a product means that it has been laboratory tested and proved to meet the efficiency standards.

This makes the task of comparing products much easier. However, it has its own disadvantages as you can find energy star on older windows while there have been newer and better ones flooding the market. Another disadvantage is that there are significant quality differences between the products which have been labeled with an Energy Star. This is why finding this symbol on a window is only the beginning of your search. The next step is finding the other specifications and markers for individual performance.


Also known as U-factor, U-value signifies the resistance to heat loss. Lower U-value means better insulation and higher means worse. To choose the perfect window for the winter days, you should search for those that have lower U-values. With better insulation, you will have more heat preserved in your homes and thus save up on those high electricity bills.


SHGC is an acronym for solar heat gain coefficient. This stands for the amount of solar radiation that a window transmits. The numbers vary from 0 to 1 and lower numbers indicate less solar heat transmission.

Windows with high SHGC are recommended for rooms which are oriented to the North. This is because those rooms have less contact with solar heat during the day. To decide whether you need high or low SHGC it is best to take in mind the rooms’ orientation, climate and amount of shading outside.


VT stands for Visual Transmittance. It is expressed with percentage and it signifies the amount of visible light that the windows let pass through. A lower percentage means that the window allows less light to enter your home. Low VT percentage is typical for windows with Low-E glass. This is because Low-E is designed to reduce solar heat gain. However, the best Low-E glass will reduce heat energy while also allowing a comfortable amount of light in the home.

Air Leakage

This signifies the amount of air that can leak through cracks in the window. Logically, if the rate is higher it signifies higher leakage and unwanted loss/gain in heat. Air leakage is common for old windows and improperly installed ones.


While U-value stands for the amount of heat lost through a window, R-value represents the window’s ability to absorb and retain heat. The best windows are the ones with low U and high R values. Both of the marks are extremely important to keep in mind when choosing a proper window for your home.

Related Article: Energy Efficient Upgrades That Will Save You Money


ER or Energy Rating is a figure that basically sums-up the efficiency points of a window. While it calculates the window score, it takes in mind its U-value, air leakage and SHGC. Energy rating is directly linked to energy stars. For a window to earn an energy star, it must have a specific energy rating. This score varies for different countries and climate zones. For instance, windows with energy stars in Canada must have a minimum of 25 points in zone 1, 29 in zone 2 and 34 in zone 3. Energy rating is a great way for customers to compare overall window efficiency between two or more products.

About Falcon WD

Falcon WD is your window replacement and door replacement specialist in Toronto. Schedule your free in-home consultation today and explore the benefits of new windows and doors.


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