What Is a Home Energy Rating, and Do You Need One?

"Home energy rating" gets used for two genuinely different things, and mixing them up is easy to do. One is a free, self-service estimate you can get online in minutes. The other is a formal, in-person assessment performed by an independently accredited professional, producing an official government-recognised certificate. Both are useful — they're just not interchangeable.

Here's what a NatHERS existing-homes rating actually involves, what it costs, and when you need the formal version rather than a quick estimate.

What a NatHERS existing-homes rating actually is

NatHERS — the Nationwide House Energy Rating Scheme — is Australia's official framework for rating a home's thermal performance, historically used for new builds assessed against architectural plans. The existing-homes pathway is newer: rather than working from drawings, an accredited assessor visits the property in person and assesses what's actually there. Stage 1 of the existing-homes framework rolled out in July 2025, with Australian governments investing $32.7 million to broaden Stage 2 access from mid-2026, building on a national field trial run with CSIRO and four major banks that delivered more than 1,000 free assessments across a range of climates and dwelling types.

The output is a Home Energy Rating Certificate with two numbers: a thermal shell star rating out of 10 (always shown to one decimal place, for example "3.8 stars," not "4 stars") reflecting how well the building envelope itself performs, and a separate Whole of Home score out of 100 that also accounts for the actual appliances, hot water system, and any solar or battery installed.

What happens during the assessor's visit

An accredited assessor walks the entire home, not just the parts you'd think to mention. That typically includes measuring room and window dimensions, recording wall, roof and floor construction and insulation levels, checking glazing type and the orientation of every window, noting ceiling fans, exhaust fans and obvious gaps or draughts, and logging the existing heating, cooling, hot water and any solar or battery systems. All of that feeds into NatHERS-approved software, which is what actually calculates the star rating and Whole of Home score — the assessor's job is to gather accurate inputs, not to eyeball a number.

What it costs

Nationally, a NatHERS existing-homes assessment commonly runs $300–$650, with a median around $420 for a typical home. Where you land in that range depends on the state, the size and complexity of the home, and whether the property is regional (travel surcharges of roughly $50–$200 are common outside major metro areas):

Typical ranges by state

• NSW, WA, ACT, NT: around $350–$650
• VIC, SA, TAS: around $300–$550
• QLD: around $300–$500

Smaller dwellings — apartments and units — tend to sit at the lower end, sometimes down to around $220–$450, since there's simply less to assess.

How this is different from your free ComfortScore

This is the distinction that matters most before you spend anything. Your free ComfortScore is a self-service estimate — you answer questions about your home online, no site visit required, and it's designed to help you explore upgrade options and see roughly where your home stands before you commit to anything. It isn't a NatHERS rating, it doesn't produce an official certificate, and it can't be used anywhere a formal NatHERS certificate is specifically required — property disclosure, some rebate programs, or compliance documentation.

A NatHERS existing-homes rating is the regulated version: an in-person assessment performed by an assessor who holds independent accreditation through a recognised accrediting body, using approved software, producing a certificate that's actually recognised for those purposes. MyCoolHome doesn't accredit assessors or issue NatHERS certificates itself — accreditation comes from the recognised bodies that govern the scheme. What MyCoolHome does is connect you with an already-accredited assessor and give that assessor the tools to run the assessment and get your certificate to you.

Do you actually need one?

A formal rating is worth booking when you're planning to sell or rent and want to get ahead of disclosure requirements, when you're weighing a major renovation and want a rigorous, appliance-inclusive number rather than a self-reported estimate, or when a specific rebate or program you're chasing requires a NatHERS certificate rather than an estimate.

Disclosure requirements vary significantly by state right now. The ACT already requires an energy efficiency rating when a home is sold or rented. NSW is moving into a voluntary disclosure phase from mid-2026, where sellers and landlords can choose to include a rating but aren't yet required to. Other states haven't legislated mandatory disclosure yet, though a nationally agreed Home Energy Ratings Disclosure Framework — released in two versions since mid-2024 — sets out how ratings will eventually be measured and disclosed once individual states move on it.

If you're just starting to explore what's worth fixing in your home, the free ComfortScore is the right first step — there's no reason to pay for a formal assessment before you even know which upgrades you're considering.

Our take

Neither version is the "better" one — they answer different questions. Use the free ComfortScore to work out what's worth looking at; book a formal NatHERS existing-homes rating with an accredited assessor when you need an official number for selling, renting, a major renovation, or a program that specifically requires one.

Frequently asked questions

Do I need architectural plans for a NatHERS existing-homes assessment?

No — that's the point of the existing-homes pathway. The assessor visits in person and records what's actually there, rather than working from drawings the way new-build assessments do. Source: NatHERS.

How much does a NatHERS existing-homes rating cost?

Commonly $300–$650 nationally, with a median around $420, varying by state, home size and regional travel surcharges. Source: My Energy Rating.

Is my free ComfortScore the same as a NatHERS rating?

No — ComfortScore is a free, self-service estimate with no site visit, useful for exploring upgrade options. A NatHERS existing-homes rating is a formal, in-person assessment by an independently accredited assessor that produces an official certificate recognised for disclosure, compliance and some rebate programs.

Is a home energy rating legally required to sell or rent my home?

It depends on your state. The ACT already requires it. NSW is moving to a voluntary disclosure phase from mid-2026, with mandatory disclosure to follow at a date not yet set. Most other states haven't legislated a requirement yet. Source: SolarQuotes.

What's actually in the certificate I get?

A thermal shell star rating out of 10 (shown to one decimal place) reflecting the building envelope, and a separate Whole of Home score out of 100 that also factors in your actual appliances, hot water and any solar or battery. Source: NatHERS.

Book an accredited assessor

Once you know what you're looking at, MyCoolHome connects you with an independently accredited NatHERS assessor to get the official number — for a sale, a rental, a renovation, or just peace of mind.

Start with your home. Then book the official rating when you're ready for one.