Key Takeaways
- SHGC (solar heat gain coefficient) is a number from 0 to 1 that shows how much of the sun’s heat passes through a window into your home.
- A lower SHGC blocks more solar heat, which suits warmer climates. A higher SHGC lets more in, which can help warm a home in cooler ones.
- SHGC is not the same as U-value. U-value measures how well a whole window resists heat moving through it, while SHGC measures the heat that comes from direct sunlight.
- Glass type, Low-E coatings, tints, window orientation and shading all affect the result, so judge the whole window rather than one number.
- You can look up window energy ratings through the Window Energy Rating Scheme (WERS).
What Is SHGC (Solar Heat Gain Coefficient)?
SHGC stands for solar heat gain coefficient. It is a number between 0 and 1 that shows how much of the sun’s heat passes through a window or door and into your home. A rating of 0 means no solar heat gets through, and a rating of 1 means all of it does.
To see why that matters, it helps to understand solar gain. Solar gain is the heat a building picks up when sunlight hits it. Some of that heat is reflected, and some is absorbed or transmitted through the material. SHGC boils all of that down to a single figure, so you can compare glass options side by side.
Windows make up a large part of any new build or renovation. Frame material, window type and glass all change how your home performs, so SHGC is one of the key figures to ask your supplier about.
How to Read an SHGC Number
Read SHGC like a percentage. An SHGC of 0.8 means roughly 80% of the solar heat reaches the inside of your home, while an SHGC of 0.3 means roughly 30% does.
Lower numbers keep rooms cooler in summer by blocking more of the sun’s heat. Higher numbers let more warmth in, which can reduce how much heating you need in winter. Neither is better on its own. The right number depends on where your home is and which way your windows face.
Should You Choose a High or Low SHGC?
It depends on your climate and the orientation of your windows. The goal is to let the sun in when you want warmth and keep it out when you do not.
Cooler climates
In cooler areas, a higher SHGC allows more solar heat through the glass, which helps warm the home. That warmth only helps if it stays inside, so insulating performance matters just as much. If you are building or renovating in the ACT, our team can talk you through double glazed windows in Canberra built for cold winters.
Warmer and mixed climates
In warmer climates, a lower SHGC lets less solar heat through and helps keep the home cooler. In mixed climates such as Melbourne, a balanced approach usually works best. For example, north-facing windows may suit a moderate SHGC combined with strong insulating performance, so they admit winter sun without overheating the home in summer.
SHGC vs U-Value: What Is the Difference?
SHGC measures how much solar heat passes through a window. U-value measures how well the whole window, frame and glass together, resists heat moving through it. A lower U-value means better insulation. Because the two measure different things, they are best considered together.
| Measure | SHGC | U-value |
|---|---|---|
| What it measures | Solar heat passing through the glass | Heat passing through the whole window by conduction |
| Scale | 0 to 1 | Watts per square metre per degree (W/m2.K) |
| What a lower number means | Less solar heat gets in | Better insulation |
| Best choice | Depends on your climate and orientation | Lower is better |
Optimising only one can leave a gap. A window with a low U-value but a high SHGC can hold in heat while still letting in too much summer sun. A window with a low SHGC but a high U-value blocks the sun but lets indoor heat escape quickly. The aim is the right balance for your home.
What Else Affects SHGC?
The glass has the biggest influence. Tints and Low-E coatings are two of the main options for controlling how much solar heat gets through. Low-E stands for low emissivity, a microscopically thin coating on the glass that reflects heat energy rather than letting it pass. Double or triple glazing and an argon gas fill between the panes then slow heat transfer further. Our energy efficient glass guide explains each option in more detail.
Beyond the glass, the overall performance of your windows depends on:
- The climate where you are building or renovating.
- The materials that sit around the windows, such as insulation and cladding.
- The design of the building, including orientation, layout, window position and size, roofing and shading.
- The glass type, including integrated glass units and their coatings.
SHGC forms one part of that combination, so it works best alongside the other figures rather than on its own.
Where to Find Window Energy Ratings
The Window Energy Rating Scheme (WERS) is the place to look up energy ratings for windows. It is run by the Australian Glass and Window Association and covers residential and commercial products. Its ratings bring together the information on window frames and glass, so you can compare products against the SHGC and U-value your project needs. You can browse it at the WERS website.
Choosing Glass With Ultimate Windows
Ultimate Windows is a family-owned business that has been making windows since 2001. We manufacture uPVC double glazed windows and doors at our factory in Wodonga, Victoria, with showrooms and installation teams in Melbourne and Canberra. Argon gas is standard in all our glass at no extra cost.
The easiest way to work out the right glass for your climate and window orientation is to talk it through with our team. Request a free measure and quote and we will walk you through the options for uPVC double glazed windows for your home, or call us on 1300 898 782.
Frequently Asked Questions
What is the SHGC value for windows?
The SHGC value for a window is a number between 0 and 1 that shows how much of the sun’s heat passes through the glass. A value of 0 means no solar heat is transmitted and 1 means all of it is. The right value depends on your climate, your window orientation and the glass you choose.
Is a higher or lower SHGC better?
Neither is better on its own. A lower SHGC blocks more solar heat and suits warmer climates, while a higher SHGC lets in more warmth and can help in cooler ones. In mixed climates a moderate SHGC often works well, and window orientation and shading also matter. Consider SHGC alongside U-value.
What is the difference between SHGC and U-value?
SHGC measures how much solar heat passes through a window, on a scale from 0 to 1. U-value measures how well the whole window, frame and glass, resists heat moving through it, and a lower U-value means better insulation. SHGC depends on your climate, while a lower U-value is better in any climate.
