Can COVID-19 be spread through air conditioning and ventilation systems and what precautions should businesses take?

May 29, 2020

As many businesses begin the process of re-starting operations, businesses and their advisors may face questions from employees, clients and visitors about what steps they should take to control the COVID-19 virus through air conditioning and ventilation systems. This short article by Nicholas Ostrowski attempts to address that question.

On 19 March 2020 the World Health Organisation published guidance on ‘Getting your workplace ready for COVID-19’. Frustratingly though, while it refers to ‘open[ing] windows and doors whenever possible to make sure the venue is well ventilated’ it doesn’t provide any assistance on the question of whether COVID-19 can be spread by air ventilation or conditioning systems and what control measures should be taken.

On 29 May 2020 the Government released amended guidance on Working Safely during coronavirus (COVID-19). This emphasises the need for good ventilation but again says very little other than to state that business should ‘check whether you need to service or adjust ventilation systems’.

Fortunately, a number of industry bodies have grasped the nettle and provided a suite of useful, technical guidance on what, exactly, businesses should do. The Federation of European Heating, Ventilation and Air Conditioning associations (REHVA) published detailed guidance in April which sets out in some detail the science behind the transmission of the virus. This has been supplemented by helpful guidance from the Chartered Institution of Building Services Engineers and also guidance from the National Association of Air Duct Specialists UK.

Taking the available guidance as a whole, the following points emerge:

  • There are two exposure mechanisms – close contact transmission through large droplets formed by coughing and sneezing which typically fall on nearby surfaces and airborne transmission through small particles which may stay airborne for hours and can be transported long distances.
  • Although the science is not entirely settled, the possibility of airborne transmission of COVID-19 through small particles via air ventilation and air conditioning systems cannot be discounted (and airborne transmission of previous SARS epidemics has been documented).
  • In buildings with mechanical ventilation systems the primary objective is to maximise the air exchange rate with outside air and to minimise the risk of any pockets of stagnant air. Business should:
    • use extended operation times for air conditioning, starting any cycle before the building starts being used (and ideally operating systems continuously)
    • In demand-controlled ventilation systems change the CO2 setpoint to a lower value (400ppm is recommended)
    • Avoid recirculating air and switch air handling units to 100% outdoor air
    • clean and maintain ventilation systems and filters appropriately but there is no need to clean ducts beyond normal duct cleaning and maintenance procedures (and indeed there may be risks in doing so if employees cleaning the equipment are exposed to contaminated particles and do not have suitable PPE)
  • In buildings without mechanical ventilation systems:
    • Open windows where possible (especially if a room has been previously occupied by others)
    • Consider using localised, portable air cleaning and disinfection devices (likely to be local HEPA filtration units or those that use germicidal UV) but be aware that because the airflow through such cleaners is typically limited, the floor area that they serve will be quite small.
  • Ensure that employees and visitors are reminded to flush toilets with the lids down and that toilet ventilation systems are working


Please also view our Covid-19 Guidance Tracker – a resource set up by our regulatory team to facilitate easier navigation of the applicable Covid-19 guidance.