The Home Energy Rating certificate: what it actually says, and how to explain it

You've just finished the site visit, the homeowner is standing next to you, and the certificate is about to land in their inbox. This is the moment that decides whether they walk away understanding what they paid for — or nodding along at numbers they don't really follow. Since the Stage 2 refresh, the certificate carries more information than it used to, which means there's more to get right in that two-minute conversation.

Here's exactly what's on it, section by section, and a plain-English way to talk through it.

Two numbers, not one

The single biggest change homeowners (and some assessors used to the old new-homes format) need adjusting to: an existing-homes certificate carries two separate numbers, not one star rating.

The Star Rating — out of 10, the building itself

This is the number most people already associate with NatHERS: a 0–10 scale reflecting the thermal performance of the building shell — how well the layout, materials, insulation, windows, orientation and shading keep the home comfortable in its local climate, independent of what's plugged in. The higher the stars, the less the home needs artificial heating and cooling to stay comfortable.

The Home Energy Rating score — out of 100, the whole home

This is the number that's new to anyone used to the old new-homes certificate: a 0–100 scale covering the energy efficiency of the home's major fixtures and appliances — hot water, heating and cooling systems, and (where relevant) solar. A score of 100 corresponds to a net-zero energy value home, and scores above 100 are possible for homes that generate more than they use. The plain-English version for a homeowner: the star rating is "how good is the shell," the 0–100 score is "how good is everything plugged into it."

The appliance breakdown

Below the two headline numbers, the certificate shows each major appliance alongside the percentage of the home's total energy cost it accounts for. This is usually the part that lands best with a homeowner in the room — it turns an abstract score into "your hot water system is the biggest single line item," which is a much easier thing to have an opinion about.

The upgrade recommendations

The certificate lists upgrade options ranked by the cost savings the assessment tool calculates for that specific home — not a generic checklist. This is the part worth walking through slowly with a client, because it's also where you can add value beyond the document itself: the certificate gives the ranked options, but you're the one who can talk through sequencing, trade-offs and what's realistic for their budget this year versus next.

The free ComfortScore vs the paid, formal certificate

This is the distinction homeowners ask about most, and it's worth having a clean answer ready. MyCool Home's free ComfortScore is a self-service, no-site-visit estimate a homeowner can get in a few minutes from their own description of the property — useful for a first look at where a home roughly stands, but it isn't a NatHERS-accredited assessment and can't be used anywhere a formal rating is actually required (a green home loan application, sale or lease disclosure, or a subsidy program). The Home Energy Rating certificate is the paid, in-person, accredited version: it requires an assessor on site, it's the document that satisfies those requirements, and it's what turns a rough estimate into a number a bank, buyer or program will actually accept.

The two-minute walkthrough

If you want a script rather than a mental checklist, this order tends to land well in the room: start with the star rating ("this is how good your walls, windows and insulation are at holding temperature"), then the 0–100 score ("this is everything plugged in — hot water, heating, cooling, solar if you have it"), then the appliance breakdown ("here's what's actually costing you"), then the upgrade list ("and here's what would move the needle most, in order"). Homeowners rarely need more detail than that on a first pass — the certificate itself has the depth if they want to go further later.

Our take

The refreshed certificate genuinely carries more useful information than the old single-star format, but only if it's explained rather than just handed over. The two-number structure is the one thing worth over-preparing for, since it's the part most likely to trip up a homeowner mid-explanation — and the part that makes you look like you know exactly what you're talking about when it doesn't.

Frequently asked questions

What are the two numbers on a Home Energy Rating certificate?

A Star Rating out of 10 for the thermal performance of the building shell, and a separate Home Energy Rating score out of 100 covering the energy efficiency of major fixtures and appliances. Source: Home Energy Rating.

What does a Home Energy Rating score of 100 actually mean?

100 corresponds to a net-zero energy value home; scores above 100 are possible for homes that generate more energy than they use. Source: Home Energy Rating.

Does the certificate include an appliance-by-appliance cost breakdown?

Yes — it shows each major appliance alongside the percentage of the home's total energy cost it accounts for, making it easy to identify the biggest contributors. Source: Home Energy Rating.

Are the upgrade recommendations generic or specific to the home?

Specific — the certificate ranks upgrade options by the cost savings the assessment tool calculates for that particular property, not a standard checklist. Source: Home Energy Rating.

Is MyCool Home's free ComfortScore the same as a Home Energy Rating certificate?

No — the ComfortScore is a self-service estimate with no site visit and no NatHERS accreditation behind it, so it can't be used anywhere a formal rating is required. The Home Energy Rating certificate is the accredited, in-person version.

How does this differ from a new-homes NatHERS certificate?

A new-homes certificate is assessed at the design stage from plans and shows a single thermal star rating; the existing-homes certificate is assessed on site against the real building and adds the second, appliance-inclusive Home Energy Rating score. Source: Transformed.

Two ways to act on this

Assessors: if you want a platform that routes homeowner demand straight to you, join the MyCool Home assessor network.

Homeowners: if you're ready to move from an estimate to the real thing, book an accredited assessor and get a certificate that actually counts.