Reading a NatHERS Result
A NatHERS thermal star rating indicates how effectively a dwelling design is expected to manage heating and cooling in its local climate. It is a modelled building-shell result, not a percentage, appliance rating or direct prediction of future energy bills.
A NatHERS star rating is often treated as a simple pass-or-fail number. In practice, it communicates something more specific: the modelled heating and cooling demand created by the design and construction of a home.
Accredited NatHERS software models the proposed dwelling in its relevant climate and assesses how the building shell responds to seasonal heat gain, heat loss and internal comfort conditions. The resulting thermal loads are converted into a rating between 0 and 10 stars.
The rating is therefore best understood as an indicator of thermal design performance. It helps show whether orientation, glazing, insulation, shading, construction and room layout are working together effectively before heating and cooling equipment is considered.
In Brief
What a NatHERS Star Rating Tells You
Rating Scale
The thermal performance result is expressed on a scale from 0 to 10 stars.
Primary Meaning
A higher rating generally indicates lower modelled heating and cooling loads for the dwelling.
Assessment Boundary
The star rating assesses thermal design and construction rather than appliances, solar generation or batteries.
The rating should not be read as a percentage. A 7 star dwelling is not simply “70 per cent efficient”, and the difference between star levels should not be interpreted as a direct percentage change in comfort or household energy costs.
Thermal Performance
What Does the Star Rating Actually Represent?
The star rating represents the modelled thermal response of the dwelling. The software estimates how much artificial heating and cooling would be needed to maintain standardised indoor comfort conditions throughout the year.
A home that loses heat quickly in winter or gains excessive heat in summer will generally produce higher modelled heating and cooling loads. A design that responds more effectively to its climate will generally require less mechanical assistance and achieve a stronger star rating.
Because Australian climates vary considerably, the software evaluates the dwelling against climate-specific conditions. The same construction strategy will not necessarily produce the same result in Sydney, Melbourne, Darwin, Hobart or a regional inland location.
The 0 to 10 Scale
How Should the NatHERS Star Scale Be Read?
Lower Rating
Higher Thermal Loads
The dwelling is expected to require more heating or cooling to maintain comfortable indoor conditions.
Intermediate Rating
Moderate Thermal Response
Some aspects of the building shell are performing effectively, while other parts of the design may still create significant seasonal loads.
Higher Rating
Lower Thermal Loads
The design and construction are expected to moderate indoor temperatures more effectively and reduce reliance on heating and cooling.
The scale provides a consistent way to compare modelled dwelling performance, but it does not mean that every home with the same rating will behave identically. The distribution of heat, sunlight and ventilation across individual rooms can still differ.
Reading the Outcome
What Does a Higher Star Rating Usually Indicate?
A higher rating generally indicates that the home should need less artificial heating and cooling under the standard NatHERS modelling assumptions. This may be the result of a more effective combination of solar control, insulation, glazing, orientation, thermal mass and room planning.
It does not necessarily mean the home contains more expensive products. A strong result may come from coordinated design decisions, while poorly placed high-performance products can still produce a weaker overall outcome.
Common Misunderstandings
What the Star Rating Does Not Tell You
It is not an energy-efficiency percentage. A rating of 7 stars should not be interpreted as 70 per cent efficiency.
It is not a future energy-bill estimate. Actual costs depend on occupancy, behaviour, equipment, tariffs, weather and energy sources.
It is not an appliance assessment. Air conditioners, hot-water systems, cooking equipment, solar PV and batteries are not directly rated by the thermal star result.
It is not a guarantee that every room will feel identical. Individual rooms may still experience different levels of solar exposure, heat loss and natural ventilation.
It is not automatically the complete approval outcome. The applicable compliance requirements depend on the jurisdiction, building type and selected approval pathway.
Comfort and Performance
Is a Higher NatHERS Rating the Same as Better Comfort?
Thermal comfort and the star rating are closely related, but they are not identical concepts. A stronger rating generally indicates that the home should require less heating and cooling to maintain the modelled comfort conditions.
In practice, the way the home feels will also be influenced by how temperatures are distributed between rooms, whether windows are opened or closed, the operation of blinds and shading, occupant preferences and the heating and cooling systems installed.
The star rating is therefore a valuable indicator of the underlying thermal design. It does not remove the need for appropriate ventilation, equipment selection, commissioning and day-to-day operation.
Rating Influences
Which Design Decisions Affect the Star Rating?
Site Response
Orientation
The relationship between the floor plan, windows, sun exposure and local climate can materially affect seasonal heating and cooling loads.
Openings
Window Design
Window area, placement, frame type, glass performance and orientation influence solar gains, conductive heat flow and natural ventilation.
Building Fabric
Insulation
Wall, roof, ceiling and floor insulation help control heat movement through the building shell, subject to correct detailing and construction.
Solar Control
Shading
Eaves, awnings, balconies, screens and neighbouring obstructions can change when and where direct solar heat enters the dwelling.
Construction
Materials and Thermal Mass
Floor, wall and roof construction affect how quickly heat enters, leaves or is stored within the home.
Internal Planning
Room Layout and Zoning
Room use, size, adjacency, ceiling height and ventilation pathways affect the heating and cooling requirements calculated for each zone.
These inputs interact. A design cannot usually be understood by looking at insulation, glazing or orientation in isolation. Improving the result often involves balancing several parts of the building shell rather than relying on one specification change.
Comparing Results
Can Two Different Homes Receive the Same Star Rating?
Yes. Two homes can achieve the same overall star rating through different combinations of design and construction measures. One may rely more heavily on compact planning and insulation, while another may benefit from orientation, shading, glazing placement or thermal mass.
The overall rating also summarises the calculated performance of multiple rooms and zones. One design may have relatively consistent room performance, while another reaches a similar overall result with greater differences between warmer and cooler parts of the home.
For this reason, the headline star result is important, but the underlying modelling can provide additional insight into which rooms and design decisions are driving the outcome.
Two Different Results
Thermal Star Rating and Whole of Home
Building-Shell Performance
Thermal Star Rating
Assesses the heating and cooling loads created by the design, construction and climate response of the dwelling.
Household Energy Performance
Whole of Home Rating
Considers major household energy uses together with onsite solar generation and battery storage where included.
The two results answer different questions. Solar panels may improve the Whole of Home rating, but they do not improve the separate thermal star rating of the building shell.
Rating Benchmarks
Where Do 6 Star and 7 Star Fit?
Six Star and 7 Star are outcomes within the same NatHERS thermal-rating scale. They are not separate assessment systems or different modelling methodologies.
6 Star NatHERS is primarily relevant to earlier requirements, legacy approvals and historical comparison. 7 Star is an important current benchmark for many new dwellings, subject to the jurisdiction, building classification and applicable approval pathway.
The required benchmark should always be confirmed for the specific project. For a direct comparison of the two rating levels, read the supporting guide to 6 Star vs 7 Star NatHERS ratings.
Residential Approval Context
Does the Star Rating Automatically Confirm Compliance?
A NatHERS star rating may form an important part of the residential energy-efficiency pathway, but it should not be treated as a universal approval outcome on its own.
The applicable requirement depends on the project location, dwelling classification, adopted regulatory provisions and selected compliance pathway. Jurisdictional variations may also affect the benchmark or documentation required.
In New South Wales, NatHERS thermal modelling may support the wider BASIX assessment and submission pathway. The NatHERS rating and BASIX Certificate remain different results with different roles in the approval process.
Design-Stage Use
How Can the Star Rating Inform the Design?
The star result is most useful when it is treated as feedback on the documented design rather than as a number obtained only at the end of the project.
Preliminary modelling can show how documented options for glazing, insulation, shading and construction affect the calculated heating and cooling loads. This allows project teams to compare rating responses before key specifications are fixed.
The assessment should still remain aligned with the project drawings and specifications. Changes to windows, insulation, materials, shading or room layouts may affect the result and should be reviewed before the certificate is relied upon for approval or construction.
Frequently Asked Questions
NatHERS Star Rating FAQs
What does a NatHERS star rating mean?
It indicates the modelled thermal performance of a dwelling on a scale from 0 to 10 stars. The result reflects the calculated heating and cooling loads created by the home’s design, construction and local climate.
Is a higher NatHERS star rating better?
Generally, a higher rating indicates lower modelled heating and cooling loads. The design is expected to maintain the modelled comfort conditions with less mechanical heating and cooling.
Does 7 stars mean the home is 70 per cent efficient?
No. The NatHERS star scale is not a percentage scale. Seven stars is a thermal-performance outcome produced from the modelled heating and cooling loads.
Does the rating predict future energy bills?
No. The star rating assesses thermal loads using standardised modelling assumptions. Actual bills depend on occupancy, behaviour, equipment efficiency, tariffs, weather and energy sources.
Are appliances included in the thermal star rating?
Appliances, hot-water systems, solar generation and batteries are not directly rated by the thermal star result. These broader household energy uses are considered through Whole of Home where that assessment applies.
Can solar panels improve the NatHERS star rating?
No. Solar PV may improve a Whole of Home result, but it does not change the separate thermal star rating of the building shell.
Can two homes with the same star rating perform differently?
Yes. Homes may reach the same overall result through different combinations of orientation, glazing, insulation, shading, construction and room planning. Individual room performance can also vary.
What happens if the design does not reach the required rating?
The model and documented design can be reviewed to identify which inputs are driving the result. Suitable changes may involve glazing, insulation, shading, construction or other documented building-shell elements.
Is the star rating the same as NatHERS?
No. NatHERS is the wider residential energy-rating framework. The thermal star rating is one result produced within that framework.
Related Guidance
Explore the Wider Residential Rating Framework
Residential Energy Assessment
Need to Confirm What the Rating Means for Your Project?
Certified Energy can review the available plans, project location and construction information to confirm the relevant NatHERS assessment requirements and identify the next modelling step.
Send Your Project Documents
