Scientific literature on the effects of ventilation on health, comfort, and productivity in non-industrial indoor environments (offices, schools, homes, etc.) has been reviewed by a multidisciplinary group of European scientists, called EUROVEN, with expertise in medicine, epidemiology, toxicology, and engineering. The group reviewed 105 papers published in peer-reviewed scientific journals and judged 30 as conclusive, providing sufficient information on ventilation, health effects, data processing, and reporting, 14 as providing relevant background information on the issue, 43 as relevant but non-informative or inconclusive, and 18 as irrelevant for the issue discussed. Based on the data in papers judged conclusive, the group agreed that ventilation is strongly associated with comfort (perceived air quality) and health [Sick Building Syndrome (SBS) symptoms, inflammation, infections, asthma, allergy, short-term sick leave], and that an association between ventilation and productivity (performance of office work) is indicated. The group also concluded that increasing outdoor air supply rates in non-industrial environments improves perceived air quality; that outdoor air supply rates below 25 l/s per person increase the risk of SBS symptoms, increase short-term sick leave, and decrease productivity among occupants of office buildings; and that ventilation rates above 0.5 air changes per hour (h-1) in homes reduce infestation of house dust mites in Nordic countries. The group concluded additionally that the literature indicates that in buildings with air-conditioning systems there may be an increased risk of SBS symptoms compared with naturally or mechanically ventilated buildings, and that improper maintenance, design, and functioning of air-conditioning systems contributes to increased prevalence of SBS symptoms.

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Several practical recommendations for design and operation of HVAC systems are presented. Following the recommendations will result in less pollution from the HVAC-system and increased indoor environmental quality.

Indoor air quality depends on a number of factors, including the outdoor air quality, ventilation, the amount of fresh air provided indoors, and the amount of air pollution derived from numerous indoor sources. Indoor environments are usually characterized by exposure to a complex mixture of different agents at very low exposures, mostly far below any known threshold level of biological effect. However, since people spend more than 90% of their time indoors, these low concentrations may have an impact on health and wellbeing. Those with asthma, allergies and other hypersensitivities are particularly vulnerable to inferior indoor environments. Dampness in buildings and combustion processes are probably the major pollution sources. The most important effects on public health are probably allergic respiratory sensitization, aggravation of allergic diseases, increased susceptability to respiratory infection and worsening of chronic obstructive lung diseases. The pollutants in the indoor air are gases and particles. The most typical inorganic gases are CO, NO 2 , CO 2 and O 3 . Important organic gases are volatile organic compounds (VOCs) including formaldehyde, phthalates and flame retardants. Combustion processes (tobacco smoke, heating, cooking, frying, grilling) are the main indoor sources of smaller nonbiological particles. Biological particles originate typically from pet allergens, house dust mites, pollen and micro‐organisms.