What’s in a star?

A NatHERS rating is a modelled estimate of the heating and cooling a home’s design would need, per square metre, under standard assumptions about how it is used.

It isn’t a meter reading, a power-bill forecast, a measure of your appliances or solar (that is the separate Whole of Home rating), or a check of how the house was built. NatHERS itself says actual energy use may vary, because the standard assumptions won’t match how every household lives.

And 7 stars isn’t a gold standard. It is the minimum the NatHERS route accepts for most new houses.

None of that makes NatHERS a bad tool. Our accredited assessors use it every day, and every compliance model rests on standard assumptions, ours included. It makes a star rating a tool, not a verdict.