We’ve all experienced walking into a room with a window and instantly feeling the temperature difference. When that happens, you can be certain the window is not energy efficient and not what you want in your home.
Fortunately, here in Australia, window rating schemes like WERS let potential buyers know how a product performs in terms of energy efficiency. Additionally, WERS-rated energy-efficient windows reduce energy costs, make your home more comfortable, allow more light inside, and reduce the chances of condensation developing.
What is WERS?
WERS stands for Window Energy Rating Scheme, which rates and labels windows, skylights, and glazed doors based on their energy efficiency for houses and buildings in Australia. It’s also a critical part of the quality assurance that you should expect from window manufacturers.
Energy Efficiency
Energy efficiency is related to how often your heating or cooling system is required to keep your home at a stable temperature. If your unit must turn on repeatedly, then the energy efficiency is low; if it doesn’t, then your energy efficiency is excellent.
One component of a house that significantly impacts energy efficiency is the windows you use. Poorly designed windows made from glass that is not energy-efficient will make it harder to keep your home at a comfortable temperature. On the other hand, well-designed windows made from high-quality, energy-efficient glass will have minimal impact on the temperature within your home. But how do you know if a window is energy-efficient?
WERS Ratings
WERS rates the annual energy impact that a window has on an entire house and accounts for the energy contribution of both the glass and the frame. The rating is performed separately for heating and cooling, meaning a window will have two ratings (one for cooling, one for heating) based on a ten-star scale.
The more stars assigned to a window, the more energy-efficient it is. More energy efficiency leads to a reduced burden on your heating/cooling system and lowers the costs associated with keeping it running. Over time, you’ll save a significant amount of money through energy efficiency.
If you live in a primarily hot climate, you’ll look for windows with a high energy rating for cooling, and the opposite if you live in a cool environment. In some cases, you might need a window that is well-rated for both. In short, when shopping for new windows, your best bet is to look for WERS-compliant manufacturers with windows possessing excellent ratings suitable for the climate you live in.
Understanding Energy Rating Labels
Let’s talk some more about understanding energy rating labels. As we mentioned, the ratings consist of two classifications: one for heating and another for cooling. You can see below an example of a WERS energy rating label. This particular product has three stars for heating and five stars for cooling.
https://build.com.au/window-energy-rating-scheme
The heating rating applies to windows that are needed to keep warmth inside (i.e., areas where you need a heating system). The cooling rating, on the other hand, is for windows that are necessary to keep the heat out. Depending on your climate, you may require good performance in one or both of these classifications.
Remember that WERS ratings are on a scale of 0 to 10. So zero stars indicate that the window performs very poorly in energy efficiency, while eight stars tell you that the window provides good energy performance.
https://www.capral.com.au/architectural-building-solutions/general-information/energy-efficiency/
Each WERS-rated product will also have a WERS certificate that contains more detailed information than the rating label. In addition to the star ratings, it provides product data that includes the values for key characteristics that determine the energy rating (which we’ll discuss in the next section). Near the bottom, it provides comparative house energy savings. These are relative to a base case window.
If a manufacturer is WERS accredited, their windows may also have a WERS compliance label and a WERS compliance certificate. The WERS label also indicates that the window is suitable for sustainable building projects and has passed the appropriate energy efficiency tests.
Window Energy Ratings
The WERS rating system is a scientifically-based, rigorous approach to measuring the annual energy impact a window can have on a whole house. It was initially developed in 1995 and applies to any climate in Australia. The rating system was established using a range of representative windows to provide a reliable, consistent benchmark. There are 17 base case windows that differ depending on whether the rating is for cooling or heating.
- Heating: the range goes from a one-star single-pane, tinted, aluminium-framed window to a five-star double-pane, Low-E, argon-filled window with a wood frame
- Cooling: the range goes from a one-star clear single-pane aluminium window to a five-star double-pane, spectrally selective, Low-E window with a wood frame
These characteristics generate the energy rating:
- U-value
- SHGC
- Air infiltration
- Condensation resistance
- Visible transmittance
- Fading
The U-value and SHGC (Solar Heat Gain Coefficient) impact the energy rating most; however, it’s essential to understand each characteristic:
The U-value indicates how well a window (or window assembly) prevents heat flow, and lower U-values provide the best insulation. Keep in mind that insulation is needed regardless of your climate. In a cold environment, insulation keeps the cold out and the warmth in; in hot weather, insulation keeps the heat out and the cold in. However, the U-value tends to be much more important in a cold climate. The U-value applies to the entire window assembly, not just the glass but the seals, frame, and spacers.
The SHGC, or Solar Heat Gain Coefficient, measures how well a window can block out the heat from sunlight. Another way of thinking about it is the amount of solar radiation that a window allows either by transmitting it through or by absorbing it and then releasing it inward. The SHGC is represented by a number between 0 and 1, with lower numbers being better for energy efficiency. The SHGC value tends to be an essential characteristic in warm climates.
Air can leak air through tiny openings in the window assembly. This air leakage, referred to as air infiltration, can cause heat loss and gain, depending on the outside temperature—and the smaller the air infiltration, the better the energy rating. This particular value depends heavily on the window operating type: sliding windows are much more susceptible to air leakage than hinged windows.
Condensation resistance (CR) denotes how well a window resists condensation from forming on the inside surface (we all know that no one wants a wet window). The CR is represented by a number between 0 and 100, where higher numbers are associated with better resistance to condensation.
And next, we have visible transmittance because one of the key purposes of a window is to increase the amount of light within a room. Visible transmittance is a number between 0 and 1, representing the amount of visible light the window can transmit. A higher number means more light is allowed through the window.
Have you ever had furniture in the sunlight that, over time, begins to fade? One of the aspects of a window with a good WERS rating is its ability to filter out the UV rays that cause fading.
The energy efficiency ratings are derived using simulations based on a typical Australian house using actual, hour-by-hour weather data. The simulation software is NatHERS, Australia’s Nationwide House Energy Rating Software.
Part of what makes WERS a fair and rigorous rating standard is that window manufacturers that want their products rated must do so through an AFRC (Australian Fenestration Rating Council) accredited organisation. Furthermore, windows that are WERS rated are also compliant with the National Construction Code (NCC) and can be used to meet regulatory requirements.
Additionally, there’s another interesting aspect of WERS; the ratings can be entered into Australia’s NatHERS to make assessment easier for a home’s overall energy rating. As with the WERS system, the ratings are stars based on a scale of 0 to 10. More stars mean less energy (and money) is needed to keep your home comfortable, and a NatHERS star rating of at least six is required in certain parts of Australia.
The WERS ratings also plug in easily into FirstRate5, a house energy rating software used by architects and designers. Because this software accepts WERS data, it’s possible to try out different windows before making a final selection.
WERS Windows
At Windows for Life, we understand the high costs and uncomfortable atmosphere that windows with low energy efficiency can cause. That’s why we manufacture windows and doors suitable for 10-star rated homes. Our uPVC windows are energy efficient and provide excellent noise reduction, security, degradation resistance, low maintenance, and durability. These windows are available in a wide variety of configurations and colours. Contact us today to learn more!
