NatHERS Energy Ratings for Existing Homes
Most homes were only ever rated, if at all, on the day they were designed. A NatHERS assessment for existing homes tells you how yours performs now. An accredited assessor visits, measures your home as it really is, and gives you a thermal star rating, a Whole of Home rating, and a clear, practical plan to improve comfort and cut running costs. No building plans required.
What is a NatHERS assessment for an existing home?
NatHERS, the Nationwide House Energy Rating Scheme, has rated new Australian homes for decades. It has now expanded to rate homes that are already built. An accredited assessor visits your home and records the details needed to model how it performs, so you do not need building plans, original drawings or any prior documentation.
The assessment gives you two results. A thermal star rating out of 10 shows how well your home holds comfortable temperatures through its design, insulation and glazing. A Whole of Home rating out of 100 shows overall energy performance, taking in your major fixed appliances and any rooftop solar. You also receive practical guidance on the improvements that would lift your home's performance the most.
Unlike a new-home assessment, which models a design before it is built, an existing-home assessment captures your home as it stands today, after every renovation, extension and appliance upgrade. That makes it a real-world picture of your comfort, your running costs, and exactly where energy is being lost.
Why rate your existing home
A rating turns guesswork into a clear plan. It is useful whether you intend to stay for decades or sell next year:
- Lower bills and better comfort. The assessment pinpoints where your home loses heat in winter and gains it in summer, so any money you spend on upgrades targets the biggest wins first.
- A smart upgrade plan. Insulation, draught sealing, glazing, shading and electrification can be prioritised by payback rather than guesswork, so you spend in the right order.
- Selling or leasing. Governments are trialling the disclosure of home energy ratings at the point of sale and lease. A strong rating gives buyers and renters confidence and can set your property apart.
- Green home finance. Banks are beginning to use energy ratings to offer discounted green home loans, so a rating may unlock better lending.
- Rental compliance. For landlords, a rating is a head start on meeting minimum energy standards for rental properties as they tighten.
What your assessment includes
The star rating (out of 10)
A measure of thermal performance, how well your home stays comfortable without mechanical heating and cooling. As a guide, a home near 10 stars stays comfortable year round with almost no heating or cooling, while a home at the low end struggles in heat and cold and costs more to run.
The Whole of Home rating (out of 100)
An overall energy performance score that adds your major fixed appliances and any solar to the thermal result. On this scale a poorly performing home sits below 40, while 100 represents a net zero energy home. It is the number that best reflects real running costs.
Your NatHERS certificate
You receive an official NatHERS certificate showing both ratings, plus tailored, prioritised recommendations for improving your home. The certificate can be used to support renovations, property listings and green finance applications.
How the assessment works
The process is straightforward and built around a single visit to your home:
- Book and tell us your goal. Whether you are planning upgrades, preparing to sell, applying for finance or getting ahead of rental standards, the purpose shapes the advice we give.
- The home visit. An accredited assessor records your home's construction, insulation, windows and glazing, shading, orientation, ventilation, and your heating, cooling, hot water and solar. No plans are needed, though any you have can help.
- The modelling. Your home's details are entered into the CSIRO's AccuRate Enterprise software, which simulates how it performs across a full year in your local climate.
- Your report and certificate. You receive your star and Whole of Home ratings, your certificate, and a clear set of prioritised upgrade recommendations, usually within a few business days.
What affects your home's rating
Your rating reflects how your home was built and what has been done to it since. The factors that matter most are:
- Insulation. Ceiling, wall and floor insulation, or the lack of it, is often the single biggest influence on an older home's rating.
- Windows and glazing. Single glazing, large unshaded glass and leaky frames lose comfort fast. Glazing upgrades and shading can make a clear difference.
- Draughts and sealing. Gaps around doors, windows, floors and downlights let conditioned air escape. Sealing is usually low cost and high value.
- Orientation and shading. Which way living areas face, and how summer sun is shaded, shapes how hard the home works to stay comfortable.
- Appliances and solar. Your heating, cooling and hot water systems, and any rooftop solar, drive the Whole of Home score. Efficient electric systems and solar lift it most.
The value of the assessment is that it shows which of these matters most for your specific home, so you are not guessing where to start.
Who it's for
- Homeowners who want a comfortable home and lower bills, and a clear plan for getting there.
- Renovators and retrofitters deciding where to spend for the best return before they start work.
- Sellers and buyers who want to understand a property's real running costs and comfort.
- Landlords and property managers preparing for minimum energy standards for rental properties.
- Finance applicants seeking green home loans that reward an efficient home.
Why choose Australian Energy Assessments
We are the most experienced team in Australia at rating homes that are already built, and existing homes are our focus, not a sideline to new construction.
We are independent. We don't sell insulation, glazing, heat pumps or solar, so the upgrade plan you receive is about your home and your budget, not a product we are trying to move.
And we make the result usable. You get plain-language advice that tells you what to do first, what it is likely to achieve, and what can wait, so the assessment turns into real comfort and real savings. Based in Melbourne, helping households understand and improve their homes across all states and territories.
Frequently asked questions
What is a NatHERS assessment for an existing home?
It is an energy rating for a home that is already built. An accredited assessor visits, records how the home is constructed and equipped, and models it to produce a thermal star rating out of 10 and a Whole of Home rating out of 100, along with practical advice to improve comfort and cut bills.
How is it different from a new-home NatHERS assessment?
A new-home assessment models a design from plans before it is built. An existing-home assessment captures the home as it actually is now, through a site visit, including every renovation and upgrade made over the years. It reflects real-world performance rather than an original design.
Do I need building plans or original documents?
No. The assessor gathers everything needed during the home visit, so plans are not required. If you do happen to have plans, insulation details or renovation records, they can help confirm hard-to-see features, but they are not essential.
What happens during the home visit?
The assessor records your home's construction and materials, insulation, windows and glazing, shading, orientation and ventilation, plus your heating, cooling, hot water and any solar. The visit is non-invasive and usually takes a couple of hours depending on the size of the home.
What do I receive at the end?
A thermal star rating out of 10, a Whole of Home rating out of 100, an official NatHERS certificate, and a set of tailored, prioritised recommendations for improving your home's performance.
What does the star rating mean?
It measures thermal comfort on a scale of 0 to 10. A home near 10 stars stays comfortable year round with very little heating or cooling, while a home at the low end is harder to keep comfortable and costs more to run.
How much does an existing-home assessment cost?
It depends on the size, complexity and location /state of your home. We provide a clear, fixed quote up front before any work begins, so there are no surprises. Contact us with your property details for a tailored price.
How long does a NatHERS assessment take?
Turnaround depends on the complexity of the design and how complete the plans are. A straightforward house is usually quick. Contact us with your plans and we'll give you a clear timeframe and quote.
What is a NatHERS certificate and why do I need it?
It is the official document showing your star rating, Whole of Home score, heating and cooling loads and climate zone. Your building surveyor or certifier uses it as evidence of energy efficiency compliance, and most new homes cannot start construction without one.
I had a Residential Efficiency Scorecard assessment. Is it still useful?
Your Scorecard certificate still describes your home's performance at the time it was assessed, so the information remains helpful. However, Scorecard and NatHERS are calculated differently and are not interchangeable. If you need a current NatHERS rating, you will need a new assessment.
Does this apply to rental properties?
Yes. A rating helps landlords and managers understand a property and prepare for minimum energy standards for rentals as they are introduced and tightened. See our rental compliance page for more on standards.
Is a NatHERS rating for existing homes mandatory?
Not at this stage. It is currently voluntary, but it is being requested more often for property sales, renovations and green finance, and governments are trialling energy rating disclosure when a home is sold or leased. Many owners choose to get ahead of that shift.
Why get one if it is not required?
Because it pays for itself in better decisions. It shows where your home wastes energy, so upgrades are targeted, and it adds credibility when selling, leasing or applying for finance. It turns a vague sense that the home is cold or expensive into a clear plan.
Will it actually help me cut energy bills?
Yes. The rating identifies exactly where comfort and energy are lost, so improvements like insulation, sealing, glazing or efficient electric appliances can be prioritised by payback rather than guesswork. Because we are independent, the advice is tailored to your home, not a product range.
Will a rating help when I sell or lease my home?
It can. As energy rating disclosure becomes more common at sale and lease, a strong rating reassures buyers and renters about comfort and running costs, and can help an efficient home stand out in a listing.
Can a rating help with green home finance?
Increasingly, yes. A number of banks now use home energy performance to offer discounted green home loans, so a NatHERS rating may support a better lending outcome. Always check the specific lender's requirements.
What software is used to calculate the rating?
The CSIRO's AccuRate Enterprise, a NatHERS-accredited modelling tool. It simulates your home's thermal performance and Whole of Home energy use across a full year using local climate data to produce a nationally consistent rating.
Who can carry out the assessment?
Only an accredited NatHERS assessor. Accreditation involves training and ongoing professional development to ensure ratings are accurate and consistent. It is always worth confirming your assessor is accredited before booking.
Find out how your home really performs.
Book a NatHERS assessment and get a clear rating plus a practical plan to improve comfort and cut running costs. Independent advice, no products to sell, just an honest picture of your home.