Ventilation consumes energy, primarily because the ventilation air is thermally conditioned, i.e., heated, cooled, and dehumidified or humidified. In mechanically ventilated buildings, the operation of ventilation fans also consumes energy. The capacity of heating and cooling equipment must also be increased as the amount of ventilation air provided increases. Thus, ventilation rates have often been minimized, particularly after the energy crisis in the early 70's, in order to reduce equipment and energy costs. Buildings, particularly those in cold climates, have also become more airtight which has reduced ventilation air flow through the building envelope. The ventilation rates selected for buildings must strike a balance between energy consumption by ventilation and the known or postulated benefits of ventilation to health and comfort.

Orme (1998) has performed one of the most comprehensive assessments of energy use for ventilation. In a set of 13 countries participating in the IEA Energy Conservation in Buildings & Community Systems Program, the energy consumption attributable to the ventilation of all buildings was estimated to equal approximately 9% of the total primary energy consumption of the countries. An estimated 3 exojoule (EJ) of energy are used annually to ventilate US residential buildings, approximately 30% of the total energy used in these buildings. In the US service sector (e.g., commercial, institutional, and government buildings), the estimated energy consumed for ventilation is ~1.5 EJ, approximately one quarter of total service-sector building energy use (Orme 1998). The annual carbon dioxide emissions attributed to ventilation are approximately 1000 and 800 million tons for the US residential and service sectors, respectively. Climate has a large influence on the energy required to thermally condition ventilation air. In Europe, most of this energy is used for heating the ventilation air. In the U.S., significant energy is used for both heating and cooling. In the humid Miami climate, 86% of the energy is used to remove moisture from the ventilation air.

In American-style commercial building ventilation systems with air recirculation, the ventilation rate often has a negligible influence on the energy consumption of fans in the ventilation system; however, energy is required to thermally condition the ventilation air. In European-style ventilation systems without air recirculation, both fan energy and energy for thermal conditioning are affected by the ventilation rate, but the common use of heat recovery from the ventilation air decreases the influence of ventilation rate on building energy consumption.