Are You Comparing Apples to Apples on Window Performance

Are you comparing apples to apples on window performance? We often hear people say these two windows have the same U-value, so they must perform the same. It's a fair assumption, but it's not always accurate because window performance isn't just about U-value. Yes, U-value tells you how much heat flows through the window. Lower is better. But SHGC, or solar heat gain coefficient, tells you how much heat from the sun passes through the glass, and that's just as important when you're trying to control comfort and performance. In Australia. Most window ratings come through WERS, the Window Energy Rating Scheme. It's a helpful system, but it uses assumptions that don't always reflect real-world conditions. Things like standard frames, install types, or generic shading. If you're building to a higher standard, or the Passive House standard, both the U-value and solar heat gain coefficient are calculated differently. They're assessed in context: the size of the window, the frame, the install method, the orientation, and how it all ties into the rest of the thermal So when comparing windows, it's worth asking, what testing system are the numbers from? Do those figures include the full frame and install method, or just the glass? Is this information being used in real design modelling, or just pulled from a catalogue? At Enduro, we don't look at window performance in isolation. We model it as part of the whole system. That means sometimes a window costs a little more, but saves a lot in comfort. thermal stability, and long-term efficiency. It's not about picking the most expensive product, it's about choosing the one that actually works for your home. Want to build with more clarity from day one? Download our guide, Before You Build: A Guide for People Who Expect More from Their Home. It's a short, visual read designed to help you avoid common traps, understand what matters most, and make confident decisions as you plan your home.