Clean Air in Schools: Why Healthier Classrooms Could Mean Fewer Sick Days

We count every day a child misses school. But how often do we check the air that might help keep them there?

Clean air in schools helps reduce exposure to airborne respiratory viruses and other indoor pollutants. Better classroom ventilation brings in fresh air, while HEPA air purifiers remove airborne particles. CO₂ monitors can identify poorly ventilated rooms. These measures may help reduce illness-related absences and support healthier learning environments, although researchers are still measuring their impact on attendance. Schools can start with simple improvements, including checking existing CO₂ monitors, maintaining ventilation and using appropriately sized air purifiers where needed.

Key Insights

• Clean air is a health measure, not a luxury. Children and teachers spend hours sharing the same indoor air.
• CO₂ monitors reveal ventilation problems. Readings above 1,500 ppm indicate poor ventilation under current guidance for England.
• HEPA filters remove airborne particles. They can complement ventilation, particularly when windows cannot remain open.
• Attendance and prevention go together. Reducing avoidable infections may help reduce disruption to learning.
• Parents can ask five simple questions. You don’t need to be an engineer to start a conversation about classroom air quality.

We Monitor School Attendance. Why Not the Air?

Picture a classroom on a cold Tuesday morning. Thirty children, one teacher, windows closed because it’s freezing outside. Someone is coughing. Someone else has a headache. By lunchtime, the room feels stuffy.

The register has been taken. Attendance is being monitored. But what about the air?

We teach children to wash their hands, cover their mouths and avoid sharing water bottles. All sensible advice. Yet when it comes to respiratory infections, we’ve been surprisingly slow to address something everyone in the classroom shares: the air they breathe.

This isn’t an argument for closing schools or keeping children at home unnecessarily. Quite the opposite. It’s about making schools healthier places to attend.

Because if we want children in classrooms, surely we should also want classrooms that help keep them well.

Why Clean Air in Schools Matters for Attendance

Schools understandably want children attending regularly. Missing lessons can affect learning, friendships and wellbeing. But illness-related absence cannot be solved by attendance targets alone.

A child who is genuinely unwell may need to stay home. A teacher who catches an infection may miss several days. And a vulnerable pupil may face greater consequences from the same illness.

COVID-19, influenza and measles can spread through infectious particles in the air. RSV also spreads through respiratory particles, although direct contact and contaminated surfaces are important transmission routes.

Crowded classrooms and inadequate ventilation can increase opportunities for respiratory infections to spread.

The goal shouldn’t be attendance at any cost. It should be healthy, sustainable attendance.

Cleaner air is one practical part of that approach.

How Do Viruses Spread Through Classroom Air?

Think about perfume. Someone sprays it at one end of a room, and a little later people elsewhere can smell it.

Airborne respiratory particles behave differently from perfume molecules, but the example illustrates something important: what enters the air doesn’t necessarily stay beside the person who released it.

When someone with a respiratory infection breathes, talks, coughs or sings, they can release virus-containing particles. Smaller particles may remain suspended and move through a room.

Ventilation dilutes and removes them. Filtration captures them.

Neither makes infection impossible, but both can reduce exposure.

For a deeper explanation, read our guide to airborne COVID-19 transmission.

Three Ways to Make Classroom Air Cleaner

1. Ventilation: Bring Fresh Air In

Ventilation means replacing indoor air with outdoor air. In some classrooms, opening windows and vents makes a substantial difference. Others rely on mechanical ventilation systems.

England’s Department for Education ventilation guidance, updated in February 2026, recommends practical measures such as partially opening windows, using higher-level windows to reduce draughts and airing rooms during breaks.

It gives an example of opening windows for 10 minutes per hour during lesson breaks.

But there’s no magical five-minute rule. The effect depends on weather, wind, room size, occupancy and window openings.

And schools must balance fresh air with warmth, outdoor pollution and safety. A freezing classroom isn’t a successful clean-air strategy either.

2. CO₂ Monitors: Make the Invisible Visible

People breathe out carbon dioxide (CO₂). In a crowded room without enough fresh air, CO₂ levels rise.

A monitor won’t tell you whether COVID or flu is present, but it can reveal how effectively a classroom is ventilated.

England’s Department for Education uses these CO₂ indicators:

CO₂ reading	What it means
Below 800 ppm	Good ventilation
800–1,500 ppm	Adequate ventilation
Above 1,500 ppm	Poor ventilation — action needed

These are ventilation indicators, not infection-risk thresholds. A low reading doesn’t guarantee that nobody will become infected.

For useful measurements, schools should use suitable NDIR CO₂ monitors and position them away from windows, doors and people’s direct breath.

The most important part isn’t buying a monitor. It’s knowing what to do when the number goes up.

3. HEPA Air Purifiers: Clean the Air When Windows Aren’t Enough

Sometimes opening windows isn’t practical. Perhaps the classroom faces a busy road, the heating struggles or the windows barely open.

Portable HEPA air purifiers can help by drawing room air through filters that capture airborne particles.

But here’s something schools should know before spending money:

A small bedroom purifier is unlikely to clean the air adequately in a busy classroom.

The important specification is CADR — Clean Air Delivery Rate — usually measured in cubic metres per hour (m³/h).

CADR tells you how much cleaned air a purifier can deliver.

And unlike ventilation, a HEPA purifier does not lower CO₂. It removes particles, not the carbon dioxide people breathe out.

How Big an Air Purifier Does a Classroom Need?

Let’s take a typical classroom measuring 8 metres long, 7 metres wide and 3 metres high.

Its volume is:

8 × 7 × 3 = 168 m³

The US CDC recommends aiming for five or more equivalent air changes per hour where feasible to reduce airborne viral particles. This is a useful planning benchmark, not a universal UK classroom requirement.

If filtration alone were providing five equivalent air changes per hour:

168 × 5 = 840 m³/h of CADR

That could mean several quieter purifiers rather than one large, noisy machine.

Existing ventilation may already provide some clean air, so schools should assess the room before deciding how much additional filtration is needed.

Before buying, check:

• CADR: Is it sufficient for the room?
• Noise: Can it run during lessons without becoming distracting?
• Filters: Are replacements available and affordable?
• Maintenance: Who will clean and replace the filters?
• Placement: Can air circulate safely around the unit?
• Safety: Avoid ozone generators and unnecessary ionising features.

A purifier switched off because it’s too noisy is an expensive classroom ornament.

For more guidance, see the US EPA’s guide to air cleaners.

Does Cleaner Air Actually Reduce School Absence?

This is where the science gets interesting — and where we need to avoid making promises the research hasn’t yet established.

We know that ventilation can dilute airborne contaminants and HEPA filtration can substantially reduce airborne particle concentrations.

But does that translate into fewer children missing school?

A 2024 Swiss classroom study followed two secondary-school classes over seven weeks.

Researchers reported a 77% reduction in average particle concentrations when portable air cleaners were operating. They also observed fewer respiratory-infection-related absences during filtration periods, but the study involved only 38 students and was too small to establish a reliable effect on infections or attendance.

Meanwhile, researchers in Norway have designed a larger randomised trial to investigate whether classroom air purifiers reduce pupil and teacher absence. The 2025 BMJ Open trial protocol explains the study.

So what can we say confidently?

Air cleaning reduces airborne particles. Reducing exposure to infectious aerosols is a sensible prevention strategy.

What we cannot yet promise is that a particular purifier will reduce absences by a specific percentage or pay for itself within a year.

That’s a reason to study the benefits properly, not a reason to ignore clean air.

Cleaner Air Isn’t Just About COVID

COVID brought airborne transmission into the spotlight, but classrooms contain more than viruses.

Indoor air can also contain dust, pollen, particulate pollution, cleaning-product emissions and other irritants.

Poor ventilation can contribute to stuffiness and discomfort. Better air quality may help concentration and reduce exposure to certain pollutants and respiratory triggers.

But HEPA filters don’t remove everything. They capture particles, not CO₂ or all chemical vapours.

Schools also need to address damp, mould, outdoor pollution and sources of indoor contaminants.

Clean air is a building-health issue, not just an infection-control issue.

What About Children Who Are Medically Vulnerable?

For some families, school infections are more than an inconvenience.

Children with certain medical conditions or weakened immune systems may face additional risks. Some children also develop prolonged symptoms after COVID-19, including Long Covid.

Not every infection causes long-term illness, but reducing avoidable infections reduces opportunities for post-infectious complications.

And an infection brought home from school doesn’t necessarily stay with the child who caught it. Vulnerable parents, grandparents and siblings may also be affected.

Cleaner classroom air provides a layer of protection that doesn’t depend entirely on individual children taking precautions.

That matters.

What Can Schools Do Without a Huge Budget?

Not every school can immediately install a sophisticated ventilation system. But that doesn’t mean nothing can be done.

Between 2021 and 2023, England’s Department for Education supplied CO₂ monitors to state-funded education and care settings and air-cleaning units to some settings with ventilation problems.

A useful first question is:

Where are those monitors now, and are they being used?

Here’s a practical starting plan:

1. Find the problem rooms. Check occupied CO₂ readings, especially during winter.
2. Fix the basics. Make sure windows, vents and existing ventilation systems work.
3. Use ventilation breaks. Increase fresh air safely between lessons where appropriate.
4. Prioritise difficult spaces. Focus on crowded or poorly ventilated rooms.
5. Consider HEPA filtration. Choose equipment suitable for the room, not simply the cheapest unit.
6. Review what changes. Monitor air quality, comfort and absence patterns without assuming every improvement is caused by filtration.

Schools should also maintain sensible illness policies, encourage appropriate rest when children are unwell and avoid unnecessary pressure on families following health guidance.

The aim is to make improvements practical and sustainable.

Five Questions Every Parent Can Ask Their School

You don’t need to arrive at the school gates carrying an air-quality engineering manual.

Start with five straightforward questions:

1. Does the school still have its Department for Education CO₂ monitors?
2. Are readings checked during occupied lessons, particularly in winter?
3. What happens when a classroom repeatedly exceeds 1,500 ppm?
4. How are ventilation systems, vents and filters maintained?
5. Has the school considered HEPA filtration where adequate ventilation is difficult?

A school may already be doing more than parents realise. Asking these questions opens a constructive conversation.

A Short Email Parents Can Copy

Subject: Classroom ventilation and indoor air quality

Dear Headteacher,

I hope you are well.

I wanted to ask how the school currently monitors and manages classroom ventilation, particularly during the colder months when windows may be closed.

I understand that the Department for Education has updated its guidance on CO₂ monitoring, ventilation and HEPA air-cleaning units.

Could you please let me know whether the school’s CO₂ monitors are still in use, how poor readings are addressed and whether any classrooms have been identified as needing additional ventilation or filtration?

I appreciate the pressures schools face and would be grateful to understand what measures are already in place.

Many thanks for your help.

Kind regards,

[Name]

The Bigger Question: Why Do We Accept Poor Indoor Air?

We wouldn’t knowingly give children unsafe drinking water.

We inspect school kitchens. We maintain fire alarms. We have rules about toilets, heating and building safety.

Yet the quality of classroom air can remain almost invisible until somebody complains.

And perhaps that’s the problem.

Dirty water looks wrong. A broken toilet is obvious. But a room full of exhaled air can look perfectly normal.

A CO₂ monitor can make poor ventilation visible. Better ventilation can improve it. A suitable HEPA purifier can provide additional particle removal.

None of these measures is a magic shield. Together, they offer practical ways to reduce avoidable exposure.

We should be able to care about attendance and infection prevention at the same time.

Children need education. They also need healthy places in which to receive it.

And teachers deserve workplaces where breathing cleaner air isn’t treated as a luxury.

Final Thoughts: Clean Air Should Be Normal

The lesson from the pandemic shouldn’t be that every winter requires emergency measures.

It should be that the buildings we use every day can be designed and managed better.

Cleaner air won’t prevent every infection, eliminate every absence or solve every problem facing schools.

But it is a sensible investment in healthier learning environments, supported by established principles of ventilation and filtration.

We already know how to measure much of the problem. We have practical ways to improve it.

The question now is whether we’re willing to make clean indoor air an ordinary part of school life.

Because children shouldn’t have to choose between being present and being protected.

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Frequently Asked Questions About Clean Air in Schools

Research, Guidance and Practical Resources

UK guidance

1. Department for Education — Ventilation and Air Quality in Education and Childcare Settings (2026)
2. Department for Education — Building Bulletin 101
3. UK Health Security Agency — Ventilation and Respiratory Infections
4. Department for Education — CO₂ Monitor and Air-Cleaning Programme

Research and international guidance

5. Swiss Classroom Air-Cleaning Study (2024)
6. BMJ Open — Classroom Air Purifiers and School Absence Trial Protocol (2025)
7. US CDC — How Much Ventilation Is Enough?
8. US Environmental Protection Agency — Guide to Air Cleaners

Related Reading on Long Covid Journey

How COVID-19 Spreads: Airborne Transmission Explained

Why shared indoor air matters and how ventilation, filtration and masks can reduce exposure.

Recurrent COVID Infections: Long-Term Risks

Why repeated infections matter beyond the immediate illness.

We’re All Bored of COVID — But That Doesn’t Mean It’s Over

Why practical prevention and compassion still matter even when public attention has moved on.

Long COVID UK: Why the UK Is Moving On While Millions Are Still Affected

The gap between public messaging and people still living with long-term consequences.

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Disclaimer

This article is for educational and awareness purposes. It discusses evidence and guidance on school ventilation, indoor air quality and respiratory infection prevention. It is not a substitute for professional building, engineering, medical or public health advice. Schools should follow applicable guidance, safety requirements and appropriate risk assessments.

Last reviewed and updated: October 2026.