Ventilation

Good ventilation is one of the most effective ways to improve indoor air quality. It reduces the build-up of exhaled air, airborne viruses, excess moisture and indoor pollutants, creating healthier and more comfortable learning environments for pupils and staff.

Why Ventilation Matters

Indoor air quality is affected by both indoor and outdoor pollution. Without enough fresh air, carbon dioxide (CO₂), airborne viruses, moisture and other indoor pollutants build up, affecting health, comfort and learning. Good ventilation helps dilute and remove these indoor pollutants, reducing the risk of airborne infections, damp and mould while improving concentration and wellbeing. Because many fine particles (PM2.5) originate outdoors, ventilation should be combined with source control and, where appropriate, air filtration.

Benefits of Good Ventilation

Reduces the build-up of exhaled air and airborne viruses, lowering the risk of spreading and catching diseases such as flu, RSV and COVID-19
Helps reduce exposure to airborne asthma and allergy triggers, and reduces damp and mould, which can worsen symptoms.
Supports better attendance by reducing illness-related absence.
Improves concentration, alertness, cognitive performance and productivity of staff and students
Helps remove indoor pollutants, moisture, odours and excess carbon dioxide.
Creates a more comfortable learning environment for pupils and staff.
Improved mental health and sleep

Warning Signs of Bad Ventilation

The room feels stuffy, stale or unusually warm.
Condensation forms on windows.
Damp patches or mould are present.
Unpleasant smells linger.
Occupants complain of tiredness, poor concentration or headaches.
CO2 monitors frequently show elevated readings.

Ventilation Tips

DfE guidance and statutory guidance include ventilation and monitoring. Review the guidance to better understand the requirements.

Review current DfE ventilation guidance and ensure staff understand how to apply it.
Fully open windows and doors before pupils arrive, during breaks and after school where safe to do so.
Use cross-ventilation by opening windows or doors on opposite sides of the room to allow air to flow through.
Open high-level windows first to reduce cold drafts.
Keep internal doors open where fire safety and safeguarding permit.
Open trickle vents or ventilation grilles where fitted.
Position desk or pedestal fans near open windows to help increase the movement of fresh air into the room where appropriate. Fans should not be relied upon as a substitute for ventilation.
Set a maximum occupancy for smaller rooms.
Where mechanical ventilation is in place, ventilation should begin ahead of the working day, ending after it finishes.
Ensure staff understand how to balance ventilation, comfort and energy efficiency throughout the year.

Lower temperatures and windier conditions will usually increase natural ventilation through openings. Partially opening windows and doors can still provide adequate ventilation.

Outdoor air quality should be considered. During periods of high outdoor pollution, natural ventilation may need to be balanced with filtration or mechanical ventilation to maintain healthy indoor air.

Current CO₂ Guidance

Carbon dioxide (CO₂) is widely used as an indicator of how effectively a space is ventilated. CO₂ does not measure pollution or viruses directly. Instead, it indicates how much exhaled air is accumulating indoors. Higher CO₂ levels generally suggest that fresh air is not entering the room quickly enough.

Current DfE guidance states that:

Good ventilation is a level under 800 ppm.
A level between 800 ppm and 1500 ppm is adequate.
If the level is over 1500 ppm, ventilation is poor.
Mechanically ventilated classrooms should achieve a daily average CO₂ concentration below 1,000 ppm.
Naturally ventilated classrooms should achieve a daily average CO₂ concentration below 1,500 ppm.
In naturally ventilated classrooms, CO₂ concentrations should not exceed 2,000 ppm for more than 20 consecutive minutes each day when occupancy is at or below the room’s design capacity.

The Health and Safety Executive (HSE) advises that CO₂ levels consistently above 1,500 ppm indicate poor ventilation and that action should be taken to improve air exchange.

Physical symptoms such as tiredness, headaches, and reduced concentration may begin to occur when indoor CO₂ levels reach approximately 1,000 ppm.

Why CO₂ Levels Matter

CO₂ provides a useful indication of how much exhaled air is accumulating indoors. However, low CO₂ levels do not necessarily mean particulate pollution or allergens are low. Monitoring other pollutants, such as PM2.5, provides a more complete picture of indoor air quality. Air quality monitoring is recommended by the DfE.

A classroom averaging 1,500 ppm CO₂ contains a greater proportion of rebreathed air than a classroom maintained closer to 800 ppm. If an infectious person is present, poorer ventilation can allow virus-containing particles from breathing, speaking or coughing to remain in the air for longer.

Improving ventilation helps dilute and remove these particles, reducing the risk of airborne infections such as COVID-19, influenza and RSV spreading within classrooms.

Recommended Indoor Air Quality Targets

Although current DfE guidance permits higher CO₂ concentrations, many organisations recommend around 800ppm because this reflects current scientific evidence, better ventilation and a lower proportion of rebreathed air:

British Council for Offices (BCO): 800 ppm.
Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA): 600–800 ppm.
Scientific Advisory Group for Emergencies (SAGE): below 800 ppm wherever possible.

These recommendations reflect growing recognition that good indoor air quality supports health, concentration and well-being.

Learning from Ireland

Ireland has taken a stronger approach to indoor air quality. The Health and Safety Authority (HSA) has introduced a Code of Practice for Indoor Air Quality, providing a formal framework for managing air quality in workplaces and educational settings.

The Code includes a benchmark of 1,000 ppm CO₂ and provides practical guidance on monitoring indoor air quality and taking action where ventilation is insufficient. Where natural ventilation cannot achieve suitable air quality, additional measures such as mechanical ventilation or air cleaning may be required.

Ireland’s Code of Practice recognises indoor air quality as an important occupational health issue and encourages routine assessment, monitoring and action where ventilation is inadequate. It provides an example of how clear national standards can support healthier educational environments.

Natural Ventilation Limitations

Ventilation alone cannot address every indoor air quality challenge. Some classrooms cannot achieve good ventilation because windows are faulty or painted shut. Other challenges are poor building design, outdoor noise, traffic pollution, security concerns or extreme weather. Up to 80% of fine particulate matter (PM2.5) found indoors can originate from outdoor sources, particularly traffic pollution. Research, including findings from the UK's SAMHE Initiative, shows that relatively little PM2.5 is generated inside classrooms; instead, it infiltrates from outside.

Simply closing windows is not a complete solution. While it may reduce the entry of outdoor pollution, it also reduces fresh air exchange, allowing carbon dioxide (CO₂), airborne viruses, moisture and other indoor pollutants to build up. Outdoor particles can also continue to enter through building cracks, doors and ventilation systems.

The most effective approach is a balanced strategy. Good ventilation should be combined with good building maintenance, source control and, where appropriate, air filtration. Together, these measures reduce both indoor-generated pollutants and harmful particles entering from outdoors, helping to create healthier learning environments throughout the year.