Ventilation is essential for the maintenance of good indoor air quality, although there is evidence to suggest that energy loss through uncontrolled or unnecessary air infiltration is excessive. In this study, estimates are presented for air change (ventilation and infiltration) energy use in non-industrial buildings for 13 countries. Various methods are used for the estimates, but they are mainly based on calculating the total annual enthalpy change needed for the conditioning of air. The potential for reduced energy use by improved ventilation control is also briefly reviewed. Considering the non-industrial building stock of the 13 countries collectively, the total annual loss of heating energy due to air change is estimated to amount to 48% of delivered space conditioning energy (including heating equipment losses). The results emphasise that air change related energy losses are as important as conduction and equipment losses (including 'flue' losses) in dissipating delivered space conditioning energy from buildings. In addition, estimated financial expenditures, as well as carbon dioxide emissions associated with this energy use are indicated. The financial expenditures are derived from the air change energy estimates using published International Energy Agency (IEA) energy pricing information. The magnitudes of the carbon dioxide emissions have been based on published IEA estimates of total emissions from energy-related sources for each country. (C) 2001 Published by Elsevier Science B.V.