Thermal simulation software such as AccuRate (formerly NatHERS), Building Energy Rating Scheme (BERS), and First Rate are simulation programs used to estimate the heating and cooling loads of a dwelling.
The programs calculate area-adjusted thermal loads using standardised behaviour by occupants for operating ventilation openings (windows and doors) and shading devices to ensure their effect on the loads is considered. The loads also include heat gains from occupants and activities such as cooking. The lower the load, the more the house can be comfortable for the occupants without needing air conditioning or heating.
The heating and cooling loads predicted by thermal simulation software do not include the efficiency of heating and cooling equipment or the fuel type used- these aspects are assessed in the BASIX Energy Index.
The BASIX Simulation method for Thermal comfort assessment accepts only the NatHERS "second-generation" simulation tools (namely AccuRate, BERS Pro and FirstRate 5). First-generation tools including NatHERS software are not accepted.