When designing homes that truly perform in Australia’s variable climate, averages don’t really cut it. That’s why the Gold Star software incorporates near extreme design temperatures — both for heating and cooling — to help builders and designers deliver comfort and efficiency all year round.
These critical values are known as the 99% winter design temperature and the 1% summer design temperature, and they’re built into every load calculation run through Gold Star.
What Are the 99% and 1% Design Temperatures?
- 99% Winter Design Temperature
This is the coldest outdoor temperature that occurs during just 1% of the heating season — meaning the system is designed to handle the coldest typical conditions without being oversized for the rest of the year. - 1% Summer Design Temperature
This is the hottest temperature exceeded just 1% of the time during summer. It ensures your cooling systems are designed for peak summer days, not average ones.
This isn’t just theoretical — it’s a tried-and-true design principle used globally in high-performance HVAC sizing, ensuring systems can keep up without being dramatically oversized. In practical terms, it means the home stays suitably warm or cool, and efficient when it matters most.
These values are standard in building science for calculating heating and cooling loads accurately, as they reflect real-world extremes while avoiding wasteful oversizing.
Why It Matters in the Real World
Many building energy models rely on climate averages, which smooth out extremes. That’s fine for annual energy estimates, but it can lead to undersized or underperforming heating and cooling systems. When designing for comfort, resilience, and real-world performance, the 99% and 1% temperature is a better metric. It strikes a smart balance between performance and efficiency, avoiding the pitfalls of both oversizing and under-designing.
Designing for average weather is a recipe for uncomfortable homes and inefficient systems. By targeting the extremes, we ensure that systems:
- Keep up with heating on the coldest mornings
- Deliver cooling performance on the hottest afternoons
- Avoid oversizing that drives up cost and decreases system efficiency
- Comply with performance-based design expectations in all Climate Zones.
Whether you’re sizing a heat pump for a cold Ballarat winter morning or preparing for a Mildura heatwave, using 99% and 1% values gets the system sizing just right.
Built Into Gold Star: Automatic & Manual Modes
To make these values easy to apply in practice, the Gold Star software includes two options:
Automatic Mode
Automatically applies 99% winter and 1% summer design temperatures for your selected town (e.g. Ballarat: -0.5°C in winter, 35.1°C in summer), based on historical climate data. This gives consistent, standards-aligned results without needing to research or guess.
Manual Mode
Overrides the defaults to reflect site-specific microclimates, unique elevation, or on-site monitoring data. This is particularly useful for rural builds, thermally sensitive homes, or specific design targets.
Real Performance, Real Comfort
By integrating both 99% and 1% design temperatures, Gold Star ensures that your heating and cooling designs are based on reality — not just compliance checkboxes or theoretical averages.
Whether you’re a performance builder, or a designer pushing the boundaries of efficient homebuilding, these features make Gold Star a reliable, professional-grade tool for real-world thermal performance.
