Question & Answer

Does the use of air conditioning spread COVID- 19?

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  • Claims have been circulated on social media that the use of air conditioning may lead to the spread of COVID-19.
  • Heating, ventilation and air conditioning (HVAC) systems are used in indoor spaces, such as offices, to provide comfortable environmental conditions of temperature and humidity (moisture in the air).
  • There are various types of HVAC systems. Ventilation systems provide clean air through the exchange of indoor and outdoor air and through filtering. Air conditioning systems provide varying temperatures and they take excess moisture from the air.
  • Air conditioning systems can be part of an integrated HVAC system, or a stand-alone system. Stand-alone air conditioning systems generally recirculate air without exchanging or mixing it with outdoor air.
  • The various types of HVAC systems means that it is not possible to generalise the results of studies that have taken place to date on the transmission of previous coronaviruses (e.g SARS) through these systems.
  • Of the studies that have taken place specifically on the transmission of COVID-19, there is not enough high quality evidence to support the claim that COVID-19 is spread through the use of HVAC systems.
  • In public spaces and buildings such as schools and offices, the World Health Organization (WHO) recommends increased ventilation through natural (e.g. opening windows) or mechanical (e.g. HVAC systems that introduce outdoor air) means, preferably without systems that recirculate the air.
  • Air conditioning and industrial ventilation systems in public spaces and buildings should be inspected, maintained, and cleaned regularly to ensure systems are working properly to prevent spreading the virus.
  • The WHO states that a well-maintained and operated HVAC system can reduce the spread of COVID-19 in indoor spaces by increasing the rate of air change, reducing recirculation of air and increasing the use of outdoor air.
  • Technical specifications and standards for HVAC systems to reduce the spread of COVID-19 in indoor spaces still need to be defined based on the results of ongoing research specific to COVID-19.
  • To protect yourself and others from COVID-19, please continue to follow public health advice to maintain social distancing and wash your hands properly and often even when in well ventilated spaces.

Things to Remember

  • Beware of claims based on a single study. Ask if there are other studies that examine the same question and ideally, a careful summary of all the relevant studies.
  • Beware of claims that are based on before and after comparisons and when people don’t say what a treatment was compared to. Remember: Ask what the treatment was compared to and whether it was a fair comparison.
  • Whenever possible, use up-to-date careful summaries (systematic reviews) of fair comparisons to inform decisions

Reviewers

  • Lead Researcher: Dr Claire Beecher, HRB-Trials Methodology Research Network & Evidence Synthesis Ireland, NUI Galway.
  • Reviewed by: Prof Declan Devane, School of Nursing and Midwifery, HRB-Trials Methodology Research Network, Evidence Synthesis Ireland & Cochrane Ireland, NUI Galway.
  • Evidence Advisor: Prof Andrew Murphy, General Practice, NUI Galway, Health Research Board Primary Care Clinical Trials Network Ireland
  • Evidence Advisor: Anne Daly, PPI Ignite, NUI Galway.
  • Journalist Advisor: Dr Claire O’Connell, Contributor, The Irish Times.