Oil boilers are now rated using the ErP (Energy Related Products) Directive and have their performance ratings shown on their energy efficiency labels as all other boilers do, the most efficient is A++ with the worst rating being a G. Modern oil boilers can be highly efficient if you use an experienced and reputable OFTEC registered engineer and there are now over 90 "A" rated oil boiler models on the market. The ErP Directive was introduced in 2015 by the European Union to reduce greenhouse gas emissions and the environmental impact of energy products. The directive enforces the development and improvement of energy-related product design to improve their energy efficiency.