Selecting The Right Solar Heat Gain Coefficient

Could you be wasting money by opting for the wrong solar heat gain coefficient?

Last week on our LinkedIn initiative #TwoCentsTuesday we asked our readers what they thought was the best solar heat gain coefficient. The results are in, and all respondents said 0.30 and higher. This is not always the case.

0.30 means that 30% of available solar heat can pass through the window. So generally, a 0.30 or higher SHGC is better if you live in a colder climate as it’s easier for the sun to heat your home. For a warmer climate, a low SHGC is preferable. Take BC’s Interior, for instance. We saw record-smashing temperatures in the Interior this year. If you’re building in this area, you’re going to want a low SHGC. 

In addition, a window that is designed with a high SHGC to allow heat in the winter time may not be appropriate given that BC’s colder months tend to be very cloudy. They would be quite effective in Winnipeg, on the other hand, where winters are colder but usually sunny enough to take advantage of a product with a high SHGC.

While climate is an important factor, it is not the only thing you should be taking into account. There are some areas of a home in a warmer climate where a low SHGC will make little difference to the overall performance of the project, and can even add unnecessary costs if the sun can instead be managed in other ways such as through building design, trees, or glass coatings. 

What is Solar Heat Gain?

At its most basic, solar heat gain is the heat transferred from the sun’s rays. Solar Heat Gain Coefficient “is the fraction of solar radiation admitted through a window, door, skylight—either transmitted directly and or absorbed, and subsequently released as heat inside the home. The lower SHGC, the less solar heat it transmits and the greater its shading ability”.

Why choosing the right SHGC is important

The SHGC you choose impacts the price of your project. If you’re selecting a window that is on the south-facing side of the home, in direct sun with no adjacent buildings or shading, you’ll want a product that has a low SHGC and lets in the least amount of solar radiation. Therefore, something low like a 0.2 rating would be best. Alternatively, let’s say the window is in an area with a large overhang and gets no direct sunlight. Selecting glass with a lower solar heat gain could increase your cost while being of no real benefit to your home’s comfort levels as the shading produced by the overhang will make it redundant. The same effect can be accomplished with trees or other obstacles.

Think about it like this: if you were to spend all your time indoors and bought the best, most expensive sunglasses, would you consider them a good investment? You may have the best sunglasses, but do you really need them? Not only do they serve no real purpose, you’re sat in your home and no one can see them anyway.

Could the money be saved and used for something more useful? Of course it could. This one’s a no-brainer. Having a window with high SHGC in these scenarios when the seasons are taken into account can also work very much to your advantage. For example, if you have an overhang or brise-soleil that provides shading in the summer but does not block the sun when it’s at a lower angle later in the year, or if you have a lot of trees that will lose their leaves in the fall. You don’t have to worry about excessive heat when it’s warm outside, but can take advantage of what sun you do get during the winter.

So what is the optimal SHGC?

In short, it depends. When considering SHGC, you should keep all these factors in mind:

1. Orientation of the house (Windows in direct sunlight can benefit from a higher SHGC)
2. Structural overhangs and other obstacles
3. Buildings in the immediate vicinity
4. Climate and the seasons

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We love to talk windows! The demand for glass is at its all-time highest, but we are working with our customers to ensure you get the products you need. Contact us as early in the process as possible so we can help secure your order and keep your project on schedule. We will guide you early on so that your supply requirements are met.

For more information on this topic (and many more!) contact our local Employee Owners at 1-888-534-3333 or drop us an email at info@centra.ca. Become a Window Geek yourself by signing up for our biweekly newsletter, which provides news, advice, and tips about the window industry and Centra events.