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Ventilation and air conditioning during the coronavirus (COVID-19) pandemic

The law requires employers to ensure an adequate supply of fresh air in the workplace and this has not changed during the pandemic.

Good ventilation, together with social distancing, keeping your workplace clean and frequent handwashing, can help reduce the risk of spreading coronavirus.

This guidance will help you identify poorly ventilated areas of your workplace and provides steps you can take to improve ventilation. It will apply in most workplaces.

Why ventilation is important
Balancing ventilation with keeping people warm
Identifying poorly ventilated areas
How to improve ventilation
Natural ventilation
Mechanical ventilation (including air conditioning)
Fans and air cleaning units
Ventilation in vehicles

Why ventilation is important

Good ventilation reduces the concentration of the virus in the air and therefore reduces the risks from airborne transmission. This happens when people breathe in small particles (aerosols) in the air after someone with the virus has occupied an enclosed area.

However, ventilation will have little or no impact on droplet or contact transmission routes.

You should consider ventilation alongside the relevant control measures required to reduce the risk of transmission as part of making your workplace COVID-secure.

Balancing ventilation with keeping people warm

Providing adequate ventilation does not mean that workplaces have to be cold.

Good ventilation is a balance between making sure workplaces are warm but keeping a flow of air going through an area.

Simple steps, such as partially opening windows, can be taken to ensure ventilation is maintained. Natural ventilation can be used with heating systems to maintain a reasonable temperature in the workplace.

Identifying poorly ventilated areas

Where your workplace (or parts of it) are poorly ventilated, you will need to improve ventilation in those areas to reduce the risk of airborne transmission.    

There are some simple ways to identify poorly ventilated areas:

  • Look for areas where there is no mechanical ventilation or no natural ventilation, such as opening windows and vents etc, unless doors are opened very frequently
  • Check that mechanical systems provide outdoor air, temperature control or both. If a system (eg a local air conditioner) is recirculating only and doesn’t have an outdoor air supply, or a separate source of outdoor air, the area is likely to be poorly ventilated
  • Identify areas that feel stuffy or smell badly
  • Use carbon dioxide (CO2) monitors to identify the CO2 levels to help decide if ventilation is poor. CO2 monitors are most effective for areas that are regularly attended by the same group of people. They are less effective in areas with low numbers of people

If you work in an environment with a complex ventilation system, for example supplying multiple floors and rooms, or old buildings, there is more guidance from the Chartered Institution of Building Services Engineers (CIBSE).

How to improve ventilation

It is more important to deal with areas that are not well ventilated. The more people occupying an area that is poorly ventilated, and the longer they remain in it, the greater the risk of transmission.

Singing, shouting and aerobic activities generate higher levels of aerosol and increase the risk further, so consider these factors when ensuring you have adequate ventilation.

The following guidelines can help you improve ventilation in your workplace depending on the existing ventilation you have.

Natural ventilation

Natural ventilation can be provided through open windows, or through other means such as vents. However, fire doors should not be propped open.

It is important not to completely close windows and doors when the area is occupied as this can result in very low levels of ventilation. 

Lower temperatures and likely windy weather conditions in the winter months will increase the natural ventilation through openings. This means you don’t need to open windows and doors as wide, so partially opening them can still provide adequate ventilation while maintaining a comfortable workplace temperature. Opening higher-level windows is likely to generate fewer draughts.

Airing rooms as frequently as you can will help improve ventilation. This involves opening all doors and windows wide to maximise the ventilation in the room. It may be easier to do this when the room is unoccupied or between uses.

If the area is still cold you could relax dress codes so people can wear extra layers and warmer clothing.

Fan convector heaters can be used provided the area is well ventilated, but they should not be used in poorly ventilated areas.

Mechanical ventilation (including air conditioning)

Mechanical ventilation brings fresh air into a building and can include air conditioning and/or heating. Systems that provide both heating and air conditioning are known as heating and ventilation air conditioning (HVAC).

To help reduce the risk:

  • continue using most types of mechanical ventilation as normal and set them to maximise fresh air and minimise recirculation
  • consider extending the operating times of HVAC systems to before and after people use work areas
  • make sure mechanical systems are maintained in line with manufacturers’ instructions

Recirculating air

Mechanical systems supplying individual rooms where recirculation modes allow higher rates of supply of fresh air to be provided to an area, should be allowed to operate. 

If you use a centralised ventilation system that circulates air to different rooms, it is recommended that you turn off recirculation and use a fresh air supply.

Recirculation units for heating and cooling that do not draw in a supply of fresh air can remain in operation provided there is a supply of outdoor air, for example windows and doors left open.

Recirculation units (including air conditioning) can mask poor ventilation as they just make an area more comfortable.

Fans and air cleaning units

Desk and ceiling fans

Desk or ceiling fans can be used provided the area is well ventilated but they should not be used in poorly ventilated areas.

Air cleaning and filtration units

Local air cleaning and filtration units can be used to reduce airborne transmission where it isn’t possible to maintain adequate ventilation.

Filtration systems, high-efficiency filters and ultraviolet-based devices are the most suitable types to use. They should be the correct size for the area they are being used in.

Ventilation in vehicles

Switch ventilation systems on while people are in the vehicle and set to drawing fresh air in, and not recirculating air.

To improve ventilation, windows can also be opened (partially if it’s cold). Heating should also be left on to keep the vehicle warm.

For vehicles that carry different passengers, such as taxis, clear the air between different passengers so the vehicle is aired before anyone else gets in.

Opening doors where it is safe to do so will help to change air quickly. Opening windows fully for a few minutes can also help to clear the air in the vehicle.

The Department for Transport guidance Coronavirus (COVID-19): taxis and PHVs has information on ventilation and making these vehicles COVID-secure.

HSE has advice on social distancing in vehicles during the pandemic.

Page last reviewed: 3 December 2020

Next review due: 31 December 2020

2020-12-03