The Nationwide House Energy Rating Scheme (NatHERS) is a star rating system (out of ten) that rates the energy efficiency of a home, based on its design.

When calculating a star rating, NatHERS Accredited Software models expected indoor temperatures based on data specific to that dwelling. This includes information on design and construction, climate and common patterns of household use. The software tools do not take into account electrical appliances in the dwelling, apart from the air flow impacts from ceiling fans.

Using the software user interface, a NatHERS Accredited Assessor enters data to develop a simulation model of the house or apartment, including:

  • size and function of rooms
  • size and specification of openings
  • building materials/windows/products
  • type of construction
  • dwelling orientation
  • location

The software will then model how much cooling or heating occupants may need to stay comfortable during a typical year. It does this by firstly simulating how the local climate heats and cools the house every hour of every day of the year.

Once internal temperatures fall outside a comfortable range, the software models the need for heating and cooling on the assumption that the occupants of the house will firstly open and close windows and any blinds or awnings to restore comfortable internal temperatures (when it makes sense to do so) before using any heating or cooling system. The total estimated annual heating and cooling requirements are then converted to a star rating out of 10 stars.