The New Normal: How to Operate your Air Conditioner Based on Scientific Evidence

  • There is still no proven scientific evidence to suggest that air conditioning can become contaminated with Coronavirus (SARS-CoV-2) and spread Covid-19.
  • Regularly opening the window and/or proper ventilation, together with other hygiene measures, can reduce the risk of transmission and thus protect people.
  • Air conditioning remains one of the preferred ways to control indoor climates not only to ensure the comfort of occupants but also to help prevent other health risks like heat-stroke.
  • Learning the appropriate way to operate your air conditioner during the new normal is essential.


Coronavirus (SARS-CoV-2) and the Importance of Ventilation

World Health Organization (WHO) recognizes the spread of Covid-19 is “primarily from person to person through small droplets from the nose or mouth, which are expelled when a person with Covid-19 coughs, sneezes, or speaks”.[1] According to a press release from National Institutes of Health (NIH) on March-17th, these respiratory droplets appear to be detectable in the air for up to three hours.[2]

Various reports, including one shared by Centers for Disease Control and Prevention (CDC)[3], examined the link between the spread of the virus and the recirculation of air in indoor environments. Although the air conditioning itself was not contaminated with the Coronavirus (SARS-CoV-2), they raised some doubts on whether air flowing generated by the AC operation could increase the risk of the virus spreading in enclosed spaces, when the ventilation is poor.

There is no evidence to show that the spread of Coronavirus (SARS-CoV-2) can originate from contaminated ventilation or contaminated air conditioners. However, it is still recommended to take the precautionary measures to ensure sufficient air renewal and maximize the safety of occupants.[4] 

Air renewal is achieved through ventilation and it is an effective way to minimize the spread of the virus in enclosed space. However, most air conditioners (like the air conditioner in your house or package air conditioners found in shops) do not have the ventilation function built-in. So, turning on and operating the air conditioner doesn’t guarantee proper air renewal between indoor and outdoor sources.

In this sense, regularly opening the window or using the ventilation fan to allow fresh air into the room should be a basic hygiene measure incorporated into everyday habits, along with social distancing and frequent hand washing.[5] By doing so could reduce the risk of transmission and increase the safety of the occupants.[6] 


What HVAC Associations are Saying

Several HVAC associations from around the world have spoken on the matter, seeking answers in relation to air conditioning, the current situation and people’s concerns.

Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH) said on its website that “at this stage, there is no evidence that COVID-19 can be spread through air conditioning systems”.[7] 

Representatives of European Heating and Ventilating Associations (REHVA) is more cautious and, in the document “REHVA COVID-19 guidance document” said that “there is also no reported data or studies to rule out the possibility of the airborne-particle route”. They recommend not to use recirculation since virus particles in return ducts can also re-enter a building when centralized air handling units are equipped with recirculation sectors. It’s further advised that the recirculation dampers should be closed (via the Building Management System or manually).[8]

By listening to the advice shared by the experts, you can be confident in the measures you need to take to create a comfortable indoor climate that is safe. 

Optimising Comfort during the New Normal

Since ventilation is vital for the prevention of Covid-19 when using air conditioners, regularly renewing the air in the occupied space is necessary but doing so might lead to poor temperature control. In countries that are approaching summer, the rising heat prompts other health risks related to heat stress conditions, like heat-stroke.[9]

The Japanese Association of Acute Medicine said that “when you are indoors, monitor the indoor temperature and adjust the set temperature of air conditioner as required while ensuring that you regularly allow fresh air into the room”.[10]

Moreover, American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) explained that “ventilation and filtration provided by heating, ventilating, and air-conditioning systems can reduce the airborne concentration of SARS-CoV-2 and thus the risk of transmission through the air.” In the same paper, they highlighted the impact of heat on individuals, saying, “unconditioned spaces can cause thermal stress to people that may be directly life-threatening and that may also lower resistance to infection”.[11] 

Taking the above into account, the following general guidelines detail the measures that should be observed to enjoy an indoor environment that is both comfortable and secure, and even help increase the occupant productivity[12]:

  • Temperature: it is the primary element of comfort. The ideal temperature according to ASHRAE and CDC recommend is between 24-27ºC during the Summer.[13]
  • Humidity: excessively high or low humidity leads to discomfort. A target range of 40%-60% relative humidity is normally used for comfort. ASHRAE recommends relative humidity below 65%.[14]
  • Air Purity: the presence of particulates, gases, as well as, viruses and bacteria, cause poor air quality with negative implications for the occupants. Air conditioning helps improve air quality with various techniques, of which the most widely used is the combination of ventilation with filtration.
  • Air Velocity / Distribution: it is important to avoid the sensation of a draft (unwanted local cooling of the body caused by air movement) caused by air conditioning. ASHRAE guidelines suggest an upper limit of air velocity in the occupied space of 0.2m/s (40 fpm), ensuring air is properly blown into the room, and properly distributed in the occupied space.[13]

By adhering to the guidelines set out by the HVAC associations, it is possible to enjoy the optimal indoor climate through the proper operation of your air conditioner without impacting your comfort. 


For any enquiries, please contact your local Hitachi Cooling & Heating specialist or contact us directly using our online form.



Documentary references (Information was correct as of July, 2020):

[1] World Health Organization (WHO)
“Q&A. How does COVID-19 spread?” (April. 17, 2020)


[2] National Institutes of Health (NIH)
“New coronavirus stable for hours on surfaces” (March. 17, 2020)


[3] Centers for Disease Control and Prevention (CDC)
Research Letter (Volume 26, Number 7—July 2020) (Early Release)
From #6 Jianyun Lu et al., “COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020,”
(April. 2, 2020) (Web: April. 23, 2020)


“COVID-19: Regular and correct maintenance of ventilation systems” (GEN - 1105.00) (April. 10, 2020)


[5] Centers for Disease Control and Prevention (CDC)
“Steps to Stay Safe” (April. 16, 2020)


[6] American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
“Statement” (April. 20, 2020):


[7] Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH)
“Common questions about COVID-19 and air conditioning and refrigeration systems”


[8] Representatives of European Heating and Ventilating Associations (REHVA)
“COVID-19 guidance document” (April. 3, 2020)


[9] Ministry of Health, Labor and Welfare, Japan
“Things to do to prevent the heatstroke, during the new way of life” (May. 29, 2020)


[10] Japanese Association of Acute Medicine
 “The proposal concerning the prevention of heatstroke under epidemic of new coronavirus infection” (June 1, 2020)


[11] ASHRAE Environmental Health Committee (EHC)
“Pandemic COVID-19 and Airborne Transmission” (approved April. 17, 2020) (Web: April. 23, 2020)


[12] American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)


[13] American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
ANSI/ASHRAE Standard 55-2013: Thermal Environmental Conditions for Human Occupancy. 


 [14] American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
ANSI/ASHRAE Standard 62.1-2016, Ventilation for Acceptable Indoor Air Quality


ꟷ Hitachi Cooling & Heating Australia ꟷ