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The Importance of SHGC Windows

Feb 23 2021

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Large, bright windows overlook Central Park

Thanks to advancements in window technology, homeowners can now choose to have windows that go above and beyond what older models used to offer. Modern windows are not just made with stronger, more durable material, they are also available in an assortment of styles that can give your home or property added curb appeal.

SHGC (solar heat gain coefficient) windows are a type of modern window design that allows property owners to track the precise metrics of their energy performance for more sustainable, cost-effective usage.

In this article, we will be talking about SHGC and how you can use this energy performance metric to your advantage. We will also be touching on other energy performance metrics that you can keep an eye out for when choosing windows for your property.

Without further ado, let’s get started!

 A living room with large SHGC windows

What are Energy Performance Ratings?

Energy performance ratings are there to assess the degree of energy efficiency that a window has. In order to be qualified as an energy-efficient window, the window must minimize the use of artificial heating and cooling for a home or building. 

NFRC vs. CSA Energy Performance Ratings

In Canada, the energy performance ratings of windows, doors, and skylights are tested using the standards set by the Canadian Standards Association (CSA). The CSA Group is a global organization based in Canada that develops standards in over 57 areas. However, there are also a number of products sold in Canada that are tested using NFRC standards as well. The National Fenestration Rating Council (NFRC) is a non-profit organization based in the United States that also establishes the standard methods for testing the energy performance of windows, doors, and skylights. 

Here is how the metrics used in the NFRC label compares with the metrics used in the CSA label for windows: 

NFRC Label For Windows in Canada CSA Label for Windows in Canada
  • Solar Heat Gain Coefficient
  • U-Factor
  • Visible Transmittance
  • Air Leakage*
  • Solar Heat Gain Coefficient
  • U-Factor
  • Visible Transmittance
  • Energy Rating*
Note: The R-Value** is an additional related metric that is not included on CSA’s/NFRC’slabels
*Found on only one type of energy performance label

**Off the energy performance label but still related and used


A Closer Look at SHGC and Other Related Energy Ratings

Solar Heat Gain Coefficient

The solar heat gain coefficient (SHGC) is the fraction of solar radiation that is able to pass through a window. The lower the SHGC rating, the less solar radiation and solar heat is transmitted through a window. 

Therefore, lower SHGC windows are able to keep your home or office cool during the summer by blocking more of the solar radiation. Meanwhile, higher SHGC windows are able to allow through more solar heat during the winter, thereby helping your home’s heating system. 

U-Factor

The U-factor is the rate of non-solar heat transfer from a warm area to a cold area. The lower the U-factor, the better the window is able to insulate an indoor area.

Visible Transmittance

Visible transmittance (VT) is the amount of visible light from the sun that can pass through a window. A window with a higher VT allows for more light into your home or office. Meanwhile, a window with a lower VT can help in reducing glare.  

Air Leakage*

Air leakage is the measure of air movement that happens around a window, door, or skylight if conditions present a difference in pressure on the two sides of the window. The lower the air leakage, the tighter the window. This contributes to the window’s insulating power.  

Energy Rating*

For CSA labels, energy rating takes into consideration three energy performance metrics: the U-factor, the SHGC, and air leakage. So although CSA labels may not feature air leakage explicitly, it is actually taken into consideration under the energy rating. 

R-Value**

The R-value does not appear in NFRC or CSA labels, however, it is often cited by contractors and manufacturers/sellers of windows. R-value is a measure of thermal resistance or the resistance to heat transfer. The higher the R-value, the more insulating power the window has. 

*Found on only one type of energy performance label

**Off the energy performance label but still related and used

Bay windows near a dining area

A Closer Look at SHGC Windows

If you’re aware of SHGC ratings as you look for new windows, you will be able to control how much solar radiation passes through to your interior spaces. The amount of solar radiation transmitted can significantly affect the temperature of the area because solar radiation carries infrared rays. Solar radiation also carries UV rays which, in unregulated amounts, can cause your interiors to fade and bleach. 

The Benefits of SHGC Windows

Artificial temperature control can potentially take up a large portion of your power bill if you do not have energy-efficient windows. To help lower such costs, we need to consider energy performance metrics that relate to:

  1. The control of solar radiation (i.e. SHGC) and; 
  2. The provision of proper insulation (i.e. U-factor, Air leakage, and R-value).  

So why does SHGC deserve particular attention? Aside from it being the sole determinant of how much solar radiation gets into the room, the best window SHGC also varies depending on your needs. 

If you live in a colder area, you would probably need a higher SHGC on your windows to help with warming your house. Meanwhile, if you live in a warmer area, you would need a lower SHGC on your windows to help keep your house cool by blocking out the infrared rays. 

And of course, if you live somewhere where you experience both cold and warm climates depending on the time of the year, you may need to have windows with a balanced level of SHGC or smart glass windows that can change their SHGC based on the time of year.  

Understanding SHGC Windows Metrics

Because SHGC is a fraction of solar radiation that can pass through, it is expressed from a value of 0.00 to 1.00 – wherein 1.00, theoretically, is the highest possible SHGC. However, It is very rare to find any kind of glass window with an SHGC of a perfect 0.00 or 1.00. 

This is because an SHGC of 0.00 would mean that no solar radiation (infrared rays, UV rays, and visible light) gets through at all; and an SHGC of 1.00 would mean that all solar radiation can get through.    

There are three main features that lower the SHGC of a window:

  1. Having more than 1 glass pane;
  2. The presence of a Low-E (low-emissivity) coating; and
  3. The presence of a reflective coating.

We mentioned that an SHGC of 1.00 is highly unlikely. To give an example of what a high, realistic SHGC is, let’s consider the SHGC of a single ⅛” uncoated piece of glass. It would be around 0.86

Now let’s consider the SHGC of a double-pane window without Low-E coatings. It would be around 0.70. This value decreases even more if Low-E and/or reflective coatings are added. 

Do All Windows Have and Indicate Their SHGC?

All windows have a specific SHGC rating, however, not all windows indicate this because not all of them are designed to be energy-efficient. So typically, you will only find the SHGC rating of a window on an NFRC or CSA label, along with an ENERGY STAR icon, and any other energy performance ratings.  

What is the Best SHGC for the Windows of My Property?

If you do not frequently use air conditioning, a higher SHGC which is in the range of 0.30 to 0.60 would be best. Meanwhile, if you use air conditioning more often and cooling is a concern for most parts of the year, it’s best to choose a window SHGC that is lower than 0.40

The alternative to making a fixed choice is to go for smart glass windows that offer an adjustable SHGC depending on your needs for the season. 

That concludes our article on the importance of knowing the SHGC for your “window shopping” needs! To ensure that you get the best windows from trusted brands, browse through our list of trusted window companies to find the best energy-efficient windows for your home.

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