When looking for replacement windows, one of the first tasks that should reach our to-do list is checking their energy ratings. Well, SHGC is one of the ratings that matter the most. It stands for Solar Heat Gain Coefficient. So, what is SHGC in windows? In short, it measures the amount of solar heat that passes through a window. If you want to learn more about it, read on! You’ll discover why it matters and how to choose a good SHGC based on your needs and the climate of your region.
Key Takeaways
- SHGC (Solar Heat Gain Coefficient) measures a window’s ability to block solar heat, with lower values indicating better resistance to solar heat gain.
- There’s no one-size-fits-all good SHGC rating, as it depends on climate: lower ratings are best for warmer regions, while higher ratings are best for colder climates.
- Understanding SHGC along with other metrics like U-Factor and Visible Transmittance can help you choose highly energy-efficient windows that can potentially lower your energy bills, protect your furniture against UV rays, and make your house feel more comfortable.
What Is SHGC in Windows?
According to the National Fenestration Rating Council, the Solar Heat Gain Coefficient (SHGC) measures “how well a product can resist unwanted heat gain, which is especially important during summer cooling season.”
In simpler terms, SHGC determines how much solar heat passes through a window or how well a window performs at blocking sun heat and keeping your house cool in the summer. This solar radiation can be transmitted directly through the window or absorbed by the window and then released into the house. This is why the right SHGC rating can help you save money on cooling costs.
SHGC is measured between 0 and 1. Lower numbers mean that the windows block more solar heat. In other words, windows with an SHGC closer to 0 are the best at blocking solar heat, while windows with an SHGC closer to 1 are the worst at blocking solar heat. Or, again, in other words, a window with a 0.30 SHGC allows 30% of solar heat in.
However, this doesn’t mean that windows with a high SHGC are not energy-efficient. There’s a catch in that! But we’ll discuss more details about this further down below.
Calculating the SHGC rating involves a wavelength-by-wavelength analysis of solar radiation which accounts for the entire window assembly, including the glass, the frame, and the sash. This ensures that the SHGC value accurately reflects the window’s performance in blocking solar heat. SHGC estimation methods include simulation models or calorimeter measurements, following NFRC standards.
Choosing the Right SHGC for Your Climate
And here’s the catch – low SHGC ratings are best for warm climates, while high SHGC ratings are best for cold climates. That’s why we can’t say that a specific SHGC rating is the best for you – ultimately, it depends on where you live. If you live in Northern Canada, you should go for high SHGC ratings (usually between 0.40 and 0.60). You want more solar heat to pass through your windows to avoid spending a fortune on heating your house.
On the other hand, if you live in a region with a warmer climate, you can go for lower SHGC ratings (usually between 0.17 and 0.30) so that your windows ensure less solar heat gain. Otherwise, you’ll spend a lot on cooling in the summer.
In short, it’s important to assess how much you spend on heating and cooling your house. Based on this, choose either high or low SHGC ratings. For example, if you live in a mixed climate and rely on heating and cooling equally, choose windows with a SHGC rating lower than 0.30. This way, you can still enjoy the sunlight in winter and avoid too much heat in summer.
In addition to climate considerations, it’s important to assess each window’s location. For example, let’s say you live in a warm climate. If one of your windows receives light only in the morning, you can go for higher SHGC ratings. If another window faces the south, this means it gets the most light throughout the day – you’ll want lower SHGC ratings for it.
What Influences SHGC in Windows?
The Solar Heat Gain Coefficient is influenced by the following:
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- The number of glass panes. The more glass panes a window has, the lower the SHGC. For example, double-pane windows usually have a SHGC of approximately 0.40, while triple-glazed windows have a low SHGC rating of approximately 0.30.
- Whether the glass has Low-E coatings and if it does – how many? Low-E coatings are added to the glass to improve its energy efficiency. Double- and triple-pane windows can have several Low-E coatings. For example, a double-pane Magic window with two Low-E coatings has an SHGC of 0.17. But another double-pane window with only one Low-E coating has an SHGC rating of 0.48.
- The frame materials and the insulating materials used in the Insulated Glass Unit (the gas fills and the warm-edge spacers, for example).
- The size of the window. Larger windows, for example, may have a higher SHGC rating.
- External shading devices like awnings, which block sunlight.
- Factors such as transmissivity, absorptivity, emissivity, and reflectivity.
SHGC and Other Window Performance Metrics
SHGC isn’t the only energy rating you should consider when buying windows. You should also pay attention to the U-factor, Visible Transmittance, and Air Leakage. They go hand in hand – for instance, a window with a good SHGC rating and a bad U-value is not an energy-efficient window.
Here are some details about other energy performance characteristics:
- The U-Factor measures the rate of heat transfer; you want lower numbers for the U-Factor (it is measured from 0.20 to 1.20).
- Visible Transmittance indicates how much light can pass through the window; it is measured from 0 to 1; you need to look for higher numbers.
- Air Leakage shows how resistant a window is to air infiltration; you should look for lower numbers, which indicate that you won’t have to deal with too many drafts around the windows.
Where to Find SHGC Ratings
SHGC ratings for windows are typically found on a rating label. This label is issued by the National Fenestration Rating Council (NFRC). The NFRC label includes the manufacturer, product description, additional information source, and energy performance ratings.
This label represents the rating of windows and doors as whole systems. It can help you determine their energy performance for cooling and heating. It also proves that the SHGC ratings are determined through reliable testing methods, which makes it easier for you to make informed decisions about energy performance.
If you want to check the SHGC ratings (and other energy ratings) of Magic windows, click here.
SHGC vs. Shading Coefficient
While doing some research on window Solar Heat Gain Coefficient, you may have stumbled upon another term that seems to indicate the same thing: shading coefficient.
Well, they seem identical at first but there’s a tiny difference: while the SHGC is measured using the entire window unit (the glazing, the frame, and everything else), the shading coefficient is measured only using the glass.
Either way, the shading coefficient isn’t used as widely anymore. Most window manufacturers measure the SHGC instead.
Eager to Install the Most Energy-Efficient Windows? Contact Magic!
Magic has brought glass production in-house. This means we can customize your windows however you want and use materials of the highest quality. We can manufacture the perfect windows that perform at their best given the climate of your region, your preferences, and your home design.
You can now book a free, in-home consultation with Magic, during which one of our project managers will assess all the details and provide all the information you need about energy ratings.
Frequently Asked Questions
What is the Solar Heat Gain Coefficient (SHGC)?
The Solar Heat Gain Coefficient (SHGC) measures how much heat passes through a window. A lower SHGC value indicates better resistance to solar heat gain.
What is a good SHGC rating for windows?
A good SHGC rating for windows is determined based on climate: higher SHGC ratings are best for cold climates, while lower SHGC ratings are best for warm climates.
Is 0.22 a good Solar Heat Gain Coefficient?
Yes, 0.22 is an excellent Solar Heat Gain Coefficient for homes in warm or mixed climates. If you live in a warm climate, you can choose a SHGC rating lower than 0.30. If you live in a cold climate, you should choose a SHGC rating higher than 0.30-0.40.
Why does SHGC matter for my home?
SHGC is crucial for managing energy bills as it helps you save money on heating and cooling costs.
How can we reduce SHGC?
You can reduce SHGC by installing Low-E coatings and external shading devices.
How can I find SHGC information for windows?
You can find SHGC information for windows on the NFRC rating label, which includes details from the manufacturer and other energy performance ratings.