Whole of Home Assessment Preparation
A smoother NatHERS Whole of Home assessment depends on confirming the project pathway, coordinating the thermal model and household systems, and ensuring the final plans and specifications match the assessed dwelling.
Preparing for a NatHERS Whole of Home assessment is not simply a matter of adding solar panels or selecting efficient appliances near the end of design.
The Whole of Home result is connected to the thermal performance of the dwelling and to the heating, cooling, hot-water, cooking, lighting, pool, spa, solar and battery information represented in the assessment. When these inputs are incomplete or inconsistent, the project may require additional assumptions, design changes or repeated modelling before certification.
The objective is therefore not only to reach an applicable rating benchmark. It is to reach that outcome using a coordinated design that can be documented, approved and constructed as assessed.
In Brief
Confirm the Pathway
Check the jurisdiction, building classification, applicable NCC provisions and whether the NatHERS Whole of Home pathway applies.
Coordinate the Inputs
Align the thermal model with the heating, cooling, hot-water, cooking, pool, spa, solar and battery systems.
Finalise the Documents
Review material changes and ensure the certificate, plans, schedules and specifications describe the same dwelling.
Early modelling does not require every product to be finalised. It does require the project team to distinguish between confirmed selections, provisional assumptions and information that must be resolved before the final certificate is issued.
Step 01
A project should not begin with the assumption that every new dwelling requires the same Whole of Home assessment or certificate.
The required pathway can depend on the project location, building classification, applicable NCC edition, state or territory adoption arrangements and the assessment method selected for the residential energy provisions.
Under the general NCC 2022 NatHERS settings, the Whole of Home benchmark is 60 for Class 1 houses and 50 for applicable Class 2 and Class 4 dwellings. Jurisdictional variations, transitional provisions and alternative assessment pathways may change what is required for a particular project.
New South Wales projects generally follow the BASIX pathway. For the relationship between the two systems, read BASIX and NatHERS Whole of Home: How Do They Work Together in NSW?
Step 02
The Whole of Home assessment builds on the heating and cooling loads produced through the NatHERS thermal model. It does not replace the thermal star rating or begin from an unrelated version of the dwelling.
The model should accurately represent the proposed plans, room zoning, construction systems, insulation, glazing, shading and local climate. A stronger thermal design can reduce the heating and cooling energy carried into the Whole of Home calculation.
A high thermal star rating does not automatically produce a compliant Whole of Home result. Efficient household systems and onsite energy may still be required. Conversely, additional solar may improve the Whole of Home rating without correcting weaknesses in the thermal design.
For a direct comparison, read NatHERS Thermal Star Rating vs Whole of Home Rating.
Step 03
Space Conditioning
Provide the system type, energy source, efficiency information, zones served and any relevant control assumptions.
Water Heating
Identify the proposed technology, energy source, efficiency and any solar or storage configuration relevant to the system.
Household Energy
Confirm relevant cooking and lighting information. Standardised assumptions apply to parts of the calculation, so a list of every portable appliance is not normally required.
Onsite Generation
Record the proposed system capacity and the roof orientation, tilt and shading conditions represented by the design documentation.
Energy Storage
Where included, identify the proposed storage capacity and ensure the battery is coordinated with the documented solar system.
Additional Loads
Provide information on pool or spa volume, pumps, filtration and heating where these elements form part of the assessed project.
The information does not always need to be final before modelling begins. The assessor should, however, know which inputs are confirmed, which are provisional and which remain unknown so that assumptions can be applied and reviewed appropriately.
Step 04
Confirmed inputs should be supported by current plans, schedules, specifications or nominated equipment information.
Provisional selections can support early modelling but should be clearly identified as items requiring later confirmation.
Unknown systems should be treated in accordance with the applicable NatHERS modelling rules rather than replaced with an unsupported preferred product.
Future installations should not be relied upon unless they are appropriately documented and accepted within the project approval pathway.
Final selections should be checked against the model before the certificate is issued or relied upon for construction.
A result based on optimistic assumptions may appear satisfactory during design but create rework when the actual equipment, roof layout or construction specification is later confirmed.
Common Coordination Problems
Thermal Model
Floor areas, glazing, shading or room layouts change after the dwelling has already been modelled.
Equipment
Heating, cooling or hot-water systems are substituted without checking the energy characteristics used in the assessment.
Solar Design
The assumed solar capacity does not fit the final roof, orientation, setbacks, plant zones or shading conditions.
Project Scope
Additional pumps, filtration or heating loads are introduced after the initial result has been reviewed.
Documentation
The final drawings and schedules do not contain the construction or system information relied upon by the assessor.
Timing
Modelling begins after the architecture, services and equipment schedules have already been fixed or tendered.
Rework is not always caused by a poor rating. It is frequently caused by a satisfactory rating that was produced using information that no longer matches the current project.
Performance Review
The most effective response depends on which part of the assessment is driving the result. A project should not automatically adopt the same solution used on another dwelling.
Review the thermal loads. Excessive heating or cooling demand may indicate that glazing, shading, insulation, orientation or construction should be reconsidered.
Review heating and cooling equipment. System type, efficiency and the areas served can materially influence the household energy result.
Review hot-water demand. Changing the hot-water technology, efficiency or energy source may produce a stronger result.
Check pools and spas. Pumps, heating and other associated loads may be significant and should be represented accurately.
Review onsite generation. A practical solar PV system can offset assessed energy demand where the roof and project documentation support it.
Correct inaccurate inputs. A weak result may reflect outdated plans, conservative assumptions or equipment information that no longer matches the design.
Assessment Strategy
Increasing solar PV can improve a Whole of Home rating by offsetting modelled household energy demand. It may be an appropriate and cost-effective part of the final response.
Solar does not, however, improve the separate NatHERS thermal star rating. It also does not resolve inefficient heating, cooling or hot-water systems, excessive thermal loads or inconsistencies between the assessment and the design documentation.
Before increasing the assumed solar capacity, confirm that:
A coordinated solution may combine an efficient thermal shell, suitable household systems and a practical solar installation rather than relying entirely on one late adjustment.
Step 05
Whole of Home modelling should be treated as an iterative design process rather than a calculation completed only once at the end of the project.
An early model can test whether the proposed thermal design and household systems are likely to achieve the required outcome. Revised options can then be compared before the project team commits to specific products or construction packages.
Early Review
Confirm the pathway, thermal basis and preliminary system strategy while design options remain open.
Design Review
Update the model when glazing, construction, equipment, pools, solar or batteries are selected.
Final Review
Confirm that the result, certificate inputs and approval documents describe the same final design.
Certification should not be treated as the point at which the design problem is first discovered. Its role is to document an assessment that has already been coordinated with the intended project.
Step 06
The certificate should be traceable to the project documentation used in the assessment. Measures relied upon to produce the rating should not exist only inside the modelling file.
A coordinated result gives the certifier, builder and project team a clearer basis for understanding which design and system selections support the rating.
After Certification
A NatHERS certificate applies to the dwelling design and system information that were assessed. It does not automatically confirm every later version of the project.
Changes that may require review include:
Relevant changes should be referred back to the assessor before the affected products are ordered or installed. A substitution should be checked using its actual thermal or energy characteristics rather than accepted only because it is described as equivalent.
Practical Project Sequence
Confirm the jurisdiction, project classification and applicable residential energy pathway.
Prepare or update the NatHERS thermal model using the current architectural documentation.
Provide known household systems, solar, battery, pool and spa information.
Review the preliminary rating and identify which inputs are driving the result.
Compare practical thermal, equipment and onsite-energy improvements where required.
Update the model when final design and system selections become available.
Issue the certificate only after the assessment and project documents have been coordinated.
Frequently Asked Questions
It means demonstrating the applicable annual energy-use requirement through the selected assessment pathway. Under the general NCC 2022 NatHERS settings, the benchmarks are 60 for Class 1 houses and 50 for applicable apartments, although jurisdictional variations and alternative pathways may apply.
Can the assessment begin before every system is selected?Yes. Preliminary modelling can begin using the available plans and documented system assumptions. The model should be updated as the glazing, construction, equipment, solar and battery information is confirmed.
Is a 7-star thermal rating enough on its own?Not where a separate annual energy-use requirement also applies. The thermal star rating assesses the dwelling shell, while Whole of Home considers household energy systems, onsite generation and battery storage.
Can solar panels solve a low Whole of Home result?Additional solar PV may improve the Whole of Home rating, but it should be practical for the roof and documented as part of the project. The assessor should also check whether thermal loads or inefficient household systems are contributing to the low result.
Do all household appliances need to be listed?No. Whole of Home includes standardised assumptions for parts of household energy use. Project-specific information is particularly important for systems such as heating, cooling, hot water, cooking, pools, spas, solar PV and batteries.
Does every NSW project need a separate Whole of Home rating?Not automatically. Applicable NSW residential projects generally follow the BASIX pathway. BASIX incorporates related energy calculations, but a BASIX Certificate and a separate NatHERS Whole of Home rating are not interchangeable documents.
What information should be sent to the assessor?Provide current plans, elevations, sections, construction and glazing information, project location and the known heating, cooling, hot-water, cooking, pool, spa, solar and battery selections.
Can the Whole of Home model be revised?Yes. The assessment can be updated as the design develops, systems are selected or alternative options are tested. The final model should reflect the documentation intended for approval and construction.
What most often delays final certification?Common delays include outdated plans, missing glazing or construction details, unresolved equipment selections, unrealistic solar assumptions and conflicting information across the drawings, schedules and model.
What happens when equipment changes after certification?A change to heating, cooling, hot water, solar, batteries, pools or other assessed systems may affect the result. The substitution should be reviewed against the model before procurement or installation.
Related Guidance
Whole of Home Project Review
Certified Energy can review the available plans, project location, thermal-modelling status and known household systems to clarify the Whole of Home pathway, required information and likely next steps.
Send Your Project Documents