The Dwelling Energy Assessment Procedure (DEAP) is adopted as the Irish official method for calculating the energy performance of dwellings.

The calculation is based on the energy balance taking into account a range of factors that contribute to annual energy usage, associated CO2 emissions and energy costs for the provision of space heating, water heating, ventilation and lighting of a dwelling.

These factors include:

• Size, geometry and exposure of the dwelling
• Materials used for construction of the dwelling
• Thermal insulation of the different elements of the building fabric
• Ventilation characteristics of the dwelling and ventilation equipment
• Efficiency, responsiveness and control characteristics of the heating system(s)
• Solar gains through glazed openings of the dwelling
• Thermal storage (mass) capacity of the dwelling
• The fuel used to provide space and water heating, ventilation and lighting
• Renewable and alternative energy generation technologies incorporated in the dwelling.

• household size and composition;
• individual heating patterns and temperatures;
• ownership and efficiency of particular domestic electrical appliances.