Coronavirus (COVID-19): guidance on reducing the risks in schools

Non-statutory guidance to ensure a low risk and supportive environment for learning and teaching.

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Ventilation and heating


This secton is informed by the latest scientific and public health advice and research from the Advisory Sub-group on education and children’s issues, Health Facilities Scotland, ARHAI Scotland and the SAGE Environmental and Modelling Group (EMG) which published updated guidance on 23 October 2020. Cognisance has also been taken of UK and European building services industry guidance (CIBSE and REHVA). This guidance has been updated to take account of the latest expert advice and guidance from HSE on ventilation and air conditioning during the coronavirus (COVID-19) pandemic. HSE has also reviewed and provided input to this updated guidance.

This section of the guidance is intended primarily for relevant local authority teams – it is not expected that headteachers or teachers should have the expertise to apply it independently. 

The key requirement for local authorities is to work with schools to identify and implement local approaches that balance the need for fresh air in key parts of the school estate with the maintenance of adequate temperatures. The latest scientific advice identifies that ventilation is an important factor in mitigating against the risk of far-field (>2m) aerosol transmission.

There is therefore a need for an appropriate supply of fresh air to assist with minimising the risk of virus infection. There is also a need to maintain indoor temperatures for reasons including user comfort, health and wellbeing, and learning and teaching. 

This guidance seeks to identify practical measures which may be incorporated to balance these issues. The precise balance to be struck, and the most effective ways of doing so, will depend heavily on local factors including building design, location and prevailing weather conditions.

Schools should ensure that risk assessments are updated regularly, in consultation with local authorities, staff, trade unions and (where applicable) PFI/NPD providers, to consider issues around ventilation and heating/warmth that are relevant to their specific environments. Drawing on local authority advice, they should consider areas of the school where air flow (including pockets of stagnant air in occupied spaces) and/or temperature may be problematic, and the strategies that may be used to address these issues and mitigate risks appropriately. 

Schools should as a minimum ensure that adequate levels of ventilation and appropriate temperatures are maintained, with reference to the School Premises Regulations. While minimum requirements vary depending on the specific part of the school estate, for classrooms the regulations stipulate 2 air changes per hour and a temperature of 17oC. Reference should also be made to the Workplace (Health, Safety and Welfare) Regulations 1992 requirements to maintain a reasonable temperature in the workplace. 

Natural ventilation and temperature 

The primary effective method of increasing natural ventilation remains the opening of external doors, vents and windows. Wherever it is practical, safe and secure to do so, and appropriate internal temperatures can be maintained in line with statutory obligations, this approach should be adopted. Keeping doors open (again, with appropriate regard to safety and security) may also help to reduce contact with door handles. 

However, internal fire doors should never be held open (unless assessed and provided with appropriate hold open and self-closing mechanisms which respond to the actuation of the fire alarm system). The Fire Safety Risk Assessment should always be reviewed before any internal doors are held open. 

Potential approaches to increase natural ventilation while balancing temperature, the suitability of which will depend on a range of local factors including weather conditions, may include: 

  • partially opening doors and windows to provide ventilation while reducing draughts 
  • opening high level windows in preference to low level to reduce draughts 
  • purging spaces by opening windows, vents and external doors (e.g. between classes, during break and lunch, when a room is unused, or at other suitable intervals if a space is occupied for long periods at a time), this may be particularly appropriate during the winter period to balance ventilation and thermal comfort
  • flexible uniform/staff dress policies to help ensure that children, young people and staff can stay warm if/when windows or doors require to be opened
  • maintaining appropriate heating strategies

Local authority CO2 monitoring programmes can support decision-making around the best strategies to adopt in specific spaces, for example by assessing the extent to which window opening is required to maintain levels of CO2 that are consistent with good ventilation.

Mechanical ventilation

Where it is not possible to keep doors and windows open while maintaining appropriate internal conditions in line with statutory obligations, and centralised or local mechanical ventilation is present, systems should wherever possible be adjusted to full fresh air. Air recirculation should be avoided or minimised as this does not introduce fresh air but moves air and therefore potentially virus around the space. If this is not possible while maintaining appropriate internal conditions, systems should be operated to achieve statutory temperature and air change rate requirements as a minimum. Additional points to assist with the practical delivery of this approach include:

  • where ventilation units have filters present enhanced precautions should be taken when changing filters, additional advice on filters can be located in the REHVA Covid guidance
  • ventilation systems should be checked or adjusted to ensure they do not automatically adjust ventilation levels due to differing occupancy levels
  • consider starting mechanical ventilation ahead of the school day and allow it to continue after classes have finished


Fan heaters, fan assisted heating systems or air conditioning within a single space may assist in maintaining appropriate temperatures, provided there is an adequate supply of fresh air into the space. Fans may also be useful to increase air flow on calm days, provided the space is already well ventilated. This approach should only be used where the balance of adequate ventilation and appropriate temperature cannot be achieved otherwise. Filter maintenance should also be carefully undertaken as noted above. Care should be taken to avoid unregulated use of ad hoc devices which may cause increased risk in terms of electrical load, inappropriate installation, cable trip hazard and potential fire or electrocution risk. 

CO2 monitors 

As set out earlier in this guidance, local authorities should ensure that all schools and day care of children services have access to CO2 monitoring, whether via mobile or fixed devices. This is to support the goal of all school and ELC buildings, including all suitable learning, teaching and childcare spaces, being assessed regularly for ventilation issues with a view to remedial action being taken where required.

Local authorities should also ensure that appropriate local reporting arrangements allow areas of persistent concern to continue to be identified and remedial action taken for any spaces that have been identified as showing higher levels of CO2. The monthly reporting of CO2 assessments should continue, as agreed with local authorities, until June 2022.

Where CO2 monitoring is not suitable for specific spaces, assessments may be undertaken by other appropriate means, depending on the ventilation systems and other arrangements already in place in school and ELC buildings. For example, large volume, low occupancy halls may be better suited to computer air flow modelling as a means of assessment.

It is important that local authority advice is sought on the use of monitors to ensure their proper specification, installation, location, calibration and effective use. When providing this advice, local authorities can have regard to the manufacturer’s instructions and HSE advice.

It should be noted that CO2 monitors cannot monitor levels of virus, but by monitoring levels of CO2, these can be used as a proxy measure.

CO2 monitors detect the amount of CO2 in a space, which will increase if adequate ventilation is not provided, thereby prompting user intervention such as opening a window or vent. The most recent scientific advice and research is that regularly used, multi-occupancy areas with CO2 levels consistently at or above 1500ppm should be prioritised for improvement.

This scientific advice and research also indicates that indoor spaces where there is likely to be an enhanced aerosol generation rate (e.g. singing/drama, indoor PE when permitted) should aim to ensure ventilation is sufficient to maintain CO2 concentrations at lower levels (a figure of 800ppm is recommended). 

Relevant local authority teams should provide clear advice on the appropriate use of CO2 monitors, including procedures to be followed by staff in the event of inappropriate levels being indicated (see table below, which sets out general guidelines as to how levels of CO2 can be used as indicators of potential actions required).

These general guidelines may require local interpretation into classroom-specific guidance to align with the types of monitoring device in use.

CO2 level below 800 PPM

  • no remedial action required as this indicates a space is likely to be well ventilated
  • background ventilation should always be maintained

CO2 level 800 to 1500 PPM

  • increase ventilation, e.g. opening windows and doors (potentially maximising opening width by derestricting subject to issues such as fire and security) or increasing the rate/duration of mechanical ventilation systems
  • purge before and after each lesson by opening windows/doors fully or adjusting timings of ventilation systems
  • limit occupancy numbers where possible
  • move high level activities such as dance, music or physical activities to well ventilated spaces

CO2 level above 1500 PPM

  • action required, which could include purge ventilation or reducing room occupancy
If CO2 level is consistently in this zone:
  • consider introducing additional natural or mechanical ventilation
  • consider reducing room occupancy or repurposing room
  • consider temporary use of air cleaning devices in exceptional circumstances where no other mitigation is achievable while continuing to work to achieve a more sustainable solution to increase ventilation

Air cleaners / HEPA filters

Air cleaning devices / HEPA filters may play a role in reducing airborne transmission of aerosols where it is not possible to maintain adequate ventilation. However, the available scientific evidence to date continues to support a primary focus on improving natural or mechanical ventilation, with CO2 monitoring playing a supporting role in identifying areas of concern.

Expert advice from groups including SAGE and HSE states that air filtration devices do not provide any ventilation, and should never be used as a substitute for efforts to improve ventilation – other actions should be undertaken to improve ventilation before, exceptionally, considering use of air cleaning devices. It is therefore important to understand that air cleaning devices must not be used as a substitute for natural or mechanical ventilation (including the opening of windows and doors) during cold weather – doing so may increase risks to staff and pupils. Further work is ongoing in relation to HEPA filtration and UV treatment, and we will consider this scientific advice as it becomes available.

The guidance from the Health and Safety Executive on air cleaning devices states: "… air cleaning units remove contaminants from the air but do not remove CO2 or improve ventilation".

Air cleaning technology is an area of active ongoing research, building on international research and experience, and we are continuing to keep this work under close review and consider its relevance for the school environment.

Local authorities should consider the HSE guidance on air cleaning devices if they are, exceptionally, considering making use of these as short-term mitigation measures in spaces where adequate ventilation cannot be achieved (for example, where CO2 monitor readings are consistently at or over 1500ppm and cannot be reduced through other mitigation measures).

The specification, installation, operation and maintenance of air cleaners/purifiers/filters is a complex topic. There are a wide variety of different machines which may appear similar without the application of specialist knowledge. Operation can be problematic due to noise, and there are potential risks associated with maintenance regimes. Local authorities should consider the use of such devices only in the exceptional circumstances outlined above, and ensure that specialist advice is engaged at all stages.


Local authorities and schools should, in consultation with staff and trade unions, ensure there are clear plans for effective implementation of local strategies. Key points to consider may include: 

  • clarity on responsibility for implementing approaches, with due regard for workload 
  • provision of instruction or signage, etc. to support implementation (e.g. with clear instructions for window/door/vent opening and mechanical system operation)
  • pragmatic, proportionate procedures to be followed in the event of any concerns around ventilation or heating, local authorities may wish to ensure that contact details are provided for relevant local authority teams or health and safety officers

Local authorities should also ensure that they put in place clear communications for staff, pupils and parents about the measures that are being taken to ensure adequate ventilation. This can help raise awareness of the importance of these measures, as well as providing reassurance.

This guidance will be kept under careful review and updated in light of emerging science and practice.



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