An Irish BER ranges from A1, the most energy-efficient rating, to G, the least efficient. The rating is based mainly on the calculated energy use per square metre each year, with factors such as insulation, heating, ventilation and renewable systems taken into account. A higher rating generally suggests lower energy demand, but your actual bills will also depend on household habits, energy prices and the home’s condition. A registered BER assessor can explain a property’s certificate and confirm its rating following an assessment.