Have you ever wondered why some houses stay warmer in the winter and cooler in the summer without excessive energy bills? The answer lies in their windows and the so-called window energy performance ratings.
If you want to discover how to guide yourself based on these metrics, keep reading! This article will tell you everything about the U-factor, Solar Heat Gain Coefficient, Visible Transmittance, and Air Leakage – the pillars of a window’s energy efficiency.
Key Takeaways
- When choosing windows, you should check their energy performance ratings, which include window U-factor, Solar Heat Gain Coefficient (SHGC), Visible Transmittance (VT), and Air Leakage (AL).
- Other metrics you may have stumbled upon include the Condensation Resistance and the light-to-solar gain (SLG). You should also pay attention to the Energy Rating (ER), which is a balance between the U-value, SHGC, and AL.
- Energy performance ratings indicate a window’s ability to prevent heat loss, manage solar gain, and improve indoor comfort.
- ENERGY STAR and NFRC certifications offer reliable standards and labeling for evaluating and comparing the energy efficiency of windows, helping consumers make informed decisions that lead to significant long-term energy savings.
What Are Window Energy Performance Ratings?
Window energy performance ratings measure how well a window prevents heat loss and controls solar gain. As per the National Fenestration Rating Council, an organization administering an independent energy performance rating and labeling system for windows and doors, homeowners looking for energy-efficient windows should pay attention to the following energy performance ratings:
- the U-factor
- the Solar Heat Gain Coefficient (SHGC)
- Visible Transmittance (VT)
- Air Leakage (AL)
- the Condensation Resistance (it is optional and measures how resistant a product is to condensation; the higher the number, the better)
In addition, you may also notice that some products have an Energy Rating (ER) and a light-to-solar gain (LSG).
So, why do window energy performance ratings matter so much? Windows, doors, and skylights account for up to 35% of house heat loss. This means that inefficient windows can significantly impact your energy bills and overall home comfort. Windows with good performance ratings can also lead to a reduced carbon footprint.
Keep reading to learn more about each window energy performance rating! But first, here’s a quick recap of what you should know about each:
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What Is the U-Factor?
The U-factor, also known as U-value, measures the rate of heat transfer through a window. In other words, it measures a window’s thermal transmittance or how well it insulates against heat loss.
The U-value of a window is measured from 0.20 to 1.20 – the lower the U-factor, the better the insulation and the higher the energy efficiency. Double- and triple-glazed windows typically have lower U-factors than single-pane windows because they are better insulated. However, glazing isn’t the only factor that influences a window’s U-factor. It also depends on frame materials, IGU spacing materials, window coatings (like Low-E coatings), and window treatments (such as Magic’s thermal blinds).
So, what U-factor should you look for when buying windows? Naturally – as we’ve already mentioned, the lower it is, the better. However, you shouldn’t jump directly to triple-glazed windows. You may not even need them. Only those living in extremely cold climates can truly benefit from triple-pane windows. That’s why the U-factor you should go for highly depends on the climate. An optimal solution for all climate zones would be Magic’s double-pane windows equipped with our retractable thermal blinds, which allow you to control how insulated your windows are and how much heat and light pass through them.
What Is the R-Value?
Now, you’re probably wondering if the U-value means the same as the R-value, right? Not really. While they both measure thermal transmittance, they are used for different materials. The U-value is used for windows, while the R-value quantifies the insulating capabilities of building materials – the insulation behind the wall surrounding a window, for example.
What Is the Solar Heat Gain Coefficient (SHGC)?
The Solar Heat Gain Coefficient (SHGC) quantifies the level of solar heat that can pass through the windows. The SHGC is measured from 0 to 1; the lower the rating, the less heat transfers through the window. For example, if a window has an SHGC rating of 0.30, it allows only 30% of solar heat to pass through, which is great for regions with hot climates. Why so? Because your windows don’t allow unwanted heat to disturb indoor comfort.
On the other hand, if you live in colder climates, you should look for a higher SHGC because you’ll likely enjoy those sun rays in winter.
Besides measuring how much solar heat passes through a window, SHGC ratings also determine how much solar radiation enters your home. As such, if your windows have a low SHGC value, they also protect your home from UV radiation, thus preventing unwanted furniture damage.
As with the U-value, SHGC is influenced by window glazing, Low-E coatings, and frame materials.
What Is Visible Transmittance (VT)?
Visible Transmittance (VT) measures how much natural light enters through a window.VT is measured from 0 to 1 – higher VT values indicate that the glass allows more natural light in.
While this metric does not indicate whether a window is well-insulated, it is just as important as the U-factor and the SHGC. First, windows with a high VT can help you save on energy because you’ll limit how much artificial lighting you’ll use. Secondly, these windows can promote your well-being. It’s well-known that sunlight can improve our mental health, boost our energy levels, and help us stay motivated, being especially important if you work from home. In fact, astudy has shown that brief indoor exposure to natural light can significantly reduce afternoon sleepiness! So, those who work from home simply must get windows with a high VT rating!
On the other hand, don’t forget that VT goes hand in hand with other energy performance ratings. It’s important to avoid getting windows with a high VT if they also have a high SHGC. Besides the pleasant natural light, these windows will let in unwanted UV rays.
The most important factors that influence a window’s VT are the number of glass panes, the number of glass coatings (if any), and how slim the frame is.
What Is Air Leakage In Windows?
Air leakage (AL) refers to how much air passes through window cracks, affecting the overall energy efficiency and indoor comfort. The NFRC and the Energy Star labels accept air leakage ratings below 0.3. The lower this metric, the better.
Now you’re probably wondering why you’d need to check the Air Leakage metric if the U-value and the SHGC are perfect, right? Well, the truth is that drafts can be linked to so many factors – air can sneak into the house through the tiniest gaps, and considering how many parts are in a window, there’s a high probability that even new windows can have a high Air Leakage rating. That’s why you should never overlook this metric, even if the others seem perfect.
For example, even if wood windows are generally well-insulated, they almost always have a higher Air Leakage rating than vinyl windows. In addition, this energy metric also depends on the materials used by the manufacturer – the warm-edge spacers, for example, or the quality and amount of gas fills. Let’s not forget about the installation – if not installed properly, you’ll undoubtedly feel drafts around your windows.
If you’re looking for quality windows manufactured from materials of the highest quality and award-winning hardware systems, contact Magic for a free consultation! We have exactly what you’re looking for!
Energy Rating (ER) and Light-to-Solar Gain (LSG)
Homeowners should also focus on the so-called Energy Rating (ER) of a window, which is a balance between the U-value, the SHGC, and Air Leakage, providing a comprehensive measure of a window’s energy efficiency.
The ER is measured between 0 and 50 – the higher the number, the better.
The Light-to-Solar Gain (LSG) is a ratio between Visible Transmittance (VT) and Solar Heat Gain Coefficient (SHGC). It is meant to help people purchase windows that allow enough light in, simultaneously blocking harmful radiation. The higher the LSG, the better.
The Role of the National Fenestration Rating Council (NFRC)
The National Fenestration Rating Council (NFRC) holds a significant position in the window industry by conducting tests, approving certifications, and labeling windows based on their energy performance ratings. This voluntary program offers consumers reliable information that helps them compare several energy-efficient products.
NFRC-certified products are independently tested. This ensures a trustworthy comparison between windows, doors, and skylights. The NFRC label breaks down a product’s energy performance, enabling informed purchasing decisions.
The best thing about these certifications is that you can check the energy ratings directly on the NFRC website. For example, you can find Magic products’ energy ratings here.
ENERGY STAR Certification for Windows
ENERGY STAR certification serves as another trustworthy toolin finding the windows that are most energy-efficient. ENERGY STAR windows should be visibly labelled with the Energy Star symbol.
In the past, the Energy Star certification required windows to have a particular U-factor and Energy Rating (ER) based on several climate zones. Today, however, they must meet the following criteria:
- Windows should have a maximum U-factor of 0.21 and a minimum Energy Rating (ER) of 34.
- To qualify as Most Efficient, windows should have a maximum U-factor of 0.18 and a minimum Energy Rating (ER) of 40.
Magic is an Energy Star Partner, and our products exceed all Energy Star requirements. This means they’re highly energy-efficient and should definitely be part of your sustainability journey.
Climate Zones and Recommended Ratings
Canada is the second-largest country in the world, so its territory obviously stretches over several climate zones. Some regions have no winters at all, others are buried under the snow. Some regions experience extreme temperatures, others have regular storms and heavy rains. That’s why the ENERGY STAR criteria were once grouped based on four climate zones – A, B, C, D; A being the warmest and D being the coldest. These were the requirements:
- Windows in climate zone A should have a maximum U-factor of 0.32 and a minimum ER of 13.
- Windows in climate zone B should have a maximum U-factor of 0.28 and a minimum ER of 17.
- Windows in climate zone C should have a maximum U-factor of 0.25 and a minimum ER of 21.
- Windows in climate zone D should have a maximum U-factor of 0.21 and a minimum ER of 25.
In 2015, however, these climate zones were downgraded to only three. As such, if you bought windows for Zone 1 (previously A), they were only suitable for that region. If you bought windows for Zone 3 (previously C or D), they would’ve worked for any region in Canada.
Nonetheless, even if the system had been simplified, it was still confusing to homeowners. Many of them didn’t know that it wasn’t enough to pick an ENERGY STAR window, they were also supposed to pay attention to the zone it was certified for.
Therefore, in 2020, the ENERGY STAR requirements changed again. All climate zones were removed and the criteria changed to those mentioned above. Nonetheless, the classification used before 2020 can help homeowners understand how energy-efficient their windows have to be to maintain indoor comfort and to lower energy bills.
Tips For Choosing Windows for Energy Efficiency
If you want to improve your home’s energy efficiency, make sure to consider these tips:
- Opt for casement and awning windows instead of sliding or double-hung windows.
- Choose double-pane windows instead of single-pane ones.
- If you think triple glazing suits your region’s climate, go for it.
- Don’t forget about Low-E coatings.
- Install window treatments that will improve energy efficiency – Magic’s retractable thermal blinds, for example.
- Don’t install aluminum windows because this material is a poor insulator. Instead, pick hybrid frames that combine different materials, including aluminum, which is highly durable. Magic’s Hybrid Fusion Frame, for example, consists of vinyl, steel, and aluminum.
- Make sure that your windows are installed by professionals; otherwise, you may have to deal with repairs and even window replacement.
- Install picture windows where possible, as they’re the most energy-efficient.
Improving Home Energy Efficiency with Magic Windows
Opting for windows with good energy ratings can boost comfort, reduce energy consumption, and lower a home’s carbon footprint. So, what windows should you go for? Naturally, the best you can find! We’re talking about Magic windows, obviously. Why so? Because some of our windows reach a U-factor of 0.13 and an ER of 47 – industry-leading ratings. These are calculated without our retractable solar shades and thermal blinds, which further improve the windows’ energy efficiency.
Here’s why Magic windows are so energy-efficient:
- Our Insulated Glass Units (IGUs) have 20-30% more gas between panes.
- Our IGUs have the best-performing warm-edge spacers and the longest-lasting insulating gas fills.
- Our frames have their corners welded.
- Our Hybrid Fusion Frame is exponentially more durable and energy-efficient than other frame materials on the market, thanks to our unique vinyl-aluminum-steel technology.
- Our frames are much thinner than our competitors’ frames, which improves the windows’ VT rating.
- Our windows can be equipped with Low-E coatings of the highest quality.
- Our windows and doors feature our fully retractable solar screens and thermal blinds, which help you control the amount of heat and visible light that passes through them.
- Our windows are installed by professionals who make sure that they’ll last 40+ years!
All these details can lead to significant savings on energy costs, and you may even be eligible to apply for the Canada Greener Homes Loan, so what are you waiting for? Book your free consultation today!
Frequently Asked Questions
What’s a good energy performance rating for windows?
As per Energy Star requirements for Canada, a window with a U-value of 0.21 and an Energy Rating (ER) of 34 is an energy-efficient window.
What is the U-factor, and why is it important?
The U-factor measures the rate at which a window transmits non-solar heat flow, and it’s important because lower U-factor values indicate better insulation and higher energy efficiency.
How does the Solar Heat Gain Coefficient (SHGC) affect my home?
The Solar Heat Gain Coefficient, or the SHGC, affects your home by measuring the amount of solar heat that enters through windows. Lower SHGC values reduce cooling costs by blocking solar heat gain, while higher values can help warm your home in colder climates.
What does the NFRC label tell me about a window’s performance?
The NFRC label provides important ratings such as U-factor, SHGC, Visible Transmittance, and Air Leakage, allowing you to compare and choose windows based on their performance. This can help you select the best windows for your specific requirements.
Are ENERGY STAR-certified windows worth the investment?
Investing in ENERGY STAR-certified windows is definitely worth it, as they can lead to reduced heating and cooling costs, lower carbon footprints, and increased home value. They also offer long-term energy bill savings and improved home comfort.
What financial incentives are available for upgrading to energy-efficient windows?
Upgrading to energy-efficient windows can make you eligible for rebates and tax incentives. These incentives can help make energy-efficient upgrades more financially feasible.