The objectives of this work are: first to determine the theoretical energy requirements per constant mien unit of outdoor air used for ventilation for a number of different climates and locations in North America and Europe; and secondly to determine the variation of this annual ventilation heating and cooling energy requirements due to the set points for temperature and humidity. The energy impact and/or trade-offs involved between bringing in outdoor air for indoor air pollution reduction and the energy required to condition this sir are investigated in this report. Long-term hourly weather data from several European and American locations were analysed to determine the average conditions of air over the period of record of the data. These data were then analysed to determine the psychometric process theoretical heating, cooling and moisture removal energy requirements for a constant mass of airflow per hour (MJ.h/kg). Summary weather data are also provided if it is desired to determine the additional effects of equipment and design. It was found that a significant amount of energy is required to condition air which is used for ventilation. The annual energy required per kg/hr of airflow varies from 22.1 MJ.h/kg for Los Angeles to 102.5 MJ.h/kg for Omaha. In Europe the range was from 45.6 MJ.h/kg for Nice to 101.1 MJ.h/kg for Saint-Hubert. In Europe most of the energy was used to heat the air to the desired set point. In American there were significant amounts of both heating and cooling required. Much of the variation was due to the amount of moisture in the air which had to be removed in air conditioning. In situation where air conditioning is used, a significant amount of this energy is used in dehumidifying the air. For example, in Miami 86% of the energy is used for moisture removal. It was found that the energy used was highly sensitive to the cooling and relative humidity set points.