Air conditioning and ventilation systems that are well-maintained and operated should not increase the risk of virus transmission. Fans are safe in single occupancy rooms. Fans for air circulation in collective spaces should be avoided when several people are present in this space.
All air conditioning and industrial ventilation systems for both residential and high occupancy buildings (government buildings, schools, hotels, and hospitals) should be inspected, maintained, and cleaned regularly to prevent transmission. Even in well-ventilated environments, people should continue following recommendations of physical distancing and frequent hand hygiene. Set temperatures between 24oC/75 oF and 27oC/ 80.5oF for cooling during the warmer weather, and RH between 50% and 60%.
If the use of fans is unavoidable, increase outdoor air exchange, and minimize air blowing from one person directly at another should be taken to reduce the potential spread of any airborne or aerosolized viruses.
High-occupancy publicly-accessed commercial properties such as stores, hotels, schools, shopping malls, restaurants, office buildings, etc. generally operate on centralized and ‘closed-system’ climate control and ventilation systems. Air conditioning may also be routinely used in homes during the summer months.
Air conditioning and ventilation are considered effective control strategies for preventing workplace infection and ill health in the hierarchy of controls (a framework used in occupational health to prioritize the controls needed for protection of human health, which is applicable also when considering health risks to the public in indoor spaces). If a ventilation system is well maintained the risk of transmission should not be significant. By well maintained, we mean that the system is inspected periodically, the most efficient filters are used, the filters are changed according to manufacturer recommendations, and the duct systems are cleaned periodically (Quian and Zheng, 2018).
If the air conditioning or ventilation system is not well maintained and operated, there are two potential mechanisms through which it could contribute to virus transmission: the system itself could recirculate contaminated air; and/or could create indoor conditions (temperature and humidity) that support virus survival.
Buildings that use a central ventilation and/or climate control system, should use the most efficient filters. Consider installing a higher efficiency filter (MERV 13 to 16, EPA 2019), or in healthcare facilities, a HEPA filter which captures viruses effectively (Perry, 2016), and where the air handler is rated for such a filter. Filters should be installed and maintained according to manufacturer recommendations. High efficiency filters are also available for residential use.
To reduce the number of days that the SARS-COV-2 virus can remain viable in the indoor environment, avoid setting climate control systems to low “cold” temperatures (below 70 F/ 21C) (Chin et al., 2020) and “dry” low humidity settings (below 40%) as these are optimal conditions for the virus to survive(Chan et al., 2011;Van Doremalen et al., 2020).
**In summary, air conditioning, ventilation, or other climate control systems that are well-maintained and operated should not increase the risk of virus transmission. **