All residential properties are given an EPC rating between A and G when they are built, sold or rented. Yet just 2 per cent of homes meet the top A and B grades, while around 85 per cent are either C or D, according to the latest English Housing Survey. Around 13 per cent - some 14.6 million - are rated E, F or G. The very lowest ratings, according to energy assessor Kevin Bolton, are given to homes that usually have archaic heating systems, such as coal fires.
The grading assessment must be done by an accredited assessor. Someone will visit your home and collect information about the property, such as size, age and features including walls, windows, lighting and the roof. These details are then run through a computer system that helps them provide a final score. Each part of the property is assessed as either very good, good, average, poor or very poor and given points.
Recommended energy - saving measures such as insulation and double glazing will boost your score - up to a maximum of 100. If your property scores 92 or more it will be given an energy rating of A. Between 81 and 91 is a B, while a score of 20 or lower is rated G.
The EPC, valid for 10 years, also estimates how much you will pay for your energy, and includes the carbon emissions produced by your home, along with recommendations on measures you can take to improve and the costs. But the rating system risks penalising those with older houses who have limited options when making their homes more energy efficient, experts warn.
Assessor Mr Bolton says the EPC is a 'blunt instrument'. He adds: 'Properties in the UK are very diverse and unfortunately the system uses a one - size - fits - all approach. The recommendations may not be suitable for your home because it does not take into account the age of the property, or the materials used to build it.
The methodology of the EPC has also not been updated since 2012, according to Martyn Reed, from Elmhurst Energy, which runs the accreditation scheme for assessors. However, he says improvements to the quality of calculations and recommendations may be introduced next year.