An Irish BER runs from A1, the most energy-efficient rating, through A2 and A3, then B, C, D, E, F and G, with G indicating the least efficient homes. The rating is based on estimated primary energy use per square metre, so a better letter generally means lower predicted energy demand for heating, hot water, lighting and ventilation. A BER is calculated using details such as insulation, windows, heating systems and renewable technologies, and it does not predict your exact household bills. A registered BER assessor issues the rating and can provide an advisory report explaining possible improvements; the final result depends on the property’s verified details and the official assessment method.