Coronavirus disease (COVID-19): Ventilation and air conditioning in public spaces and buildings

Ventilation is the intentional introduction of fresh air into a space while the stale air is removed. It is done to maintain the quality of air in that space.

WHO has contributed to guidance on ventilation and air-conditioning systems in the context of COVID-19, available here.

WHO works closely with the World Meteorological Organization Joint Office for Climate and Health and the United States National Oceanic and Atmospheric Administration (NOAA) through the Global Heat Health Information Network to develop and update this guidance.

Ventilation is an important factor in preventing the virus that causes COVID-19 from spreading indoors.  Below are steps to consider which can improve indoor ventilation. These steps should be considered in consultation with a heating, ventilation and air conditioning (HVAC) professional.

• Consider using natural ventilation, opening windows if possible and safe to do so.
• For mechanical systems, increase the percentage of outdoor air, using economizer modes of HVAC operations and potentially as high as 100%. Before increasing outdoor air percentage, verify compatibility with HVAC system capabilities for both temperature and humidity control as well as compatibility with outdoor/indoor air quality considerations.
• Increase total airflow supply to occupied spaces, if possible.
• Disable demand-control ventilation controls that reduce air supply based on temperature or occupancy.
• Improve central air filtration:
  • Increase air filtration to as high as possible without significantly diminishing design airflow.
  • Inspect filter housing and racks to ensure appropriate filter fit and check for ways to minimize filter bypass.
• Consider running the HVAC system at maximum outside airflow for 2 hours before and after spaces are occupied, in accordance with manufactory recommendations.
• Generate clean-to-less-clean air movements by re-evaluating the positioning of supply and exhaust air diffusers and/or dampers and adjusting zone supply and exhaust flow rates to establish measurable pressure differentials. Have staff work in “clean” ventilation zones that do not include higher-risk areas such as visitor reception or exercise facilities (if open).
• Ensure exhaust fans in restroom facilities are functional and operating at full capacity when the building is occupied.

In all workplaces, schools and tourist accommodations, there should be fresh, clean air. WHO recommends an increased ventilation rate through natural or mechanical means, preferably without recirculation of the air. In case of air recirculation, filters should be cleaned regularly, especially for jobs that place an individual at a medium or high risk of exposure to COVID-19. Examples of such jobs may include frontline workers in retail, tourist accommodation and domestic workers.