Various studies have shown that we spend up to 90% of our time indoors, whether at home, work, education or leisure. Indoor air quality (IAQ) is becoming increasing important, as building envelopes become more energy efficient (trapping air in), and we learn about the health and wellbeing impact on building occupants. 

IAQ refers to the quality of air within buildings, and is influenced by various factors, including the presence of pollutants, temperature, humidity, and ventilation. Poor indoor air quality can have adverse effects on health, such as respiratory problems, allergies, and cardiovascular issues.

Heating, ventilation, and air conditioning (HVAC) systems are central to creating healthy indoor environments. To maintain good indoor air quality, it is essential to identify, control and reduce sources of pollutants via filtration or purification, ensure proper ventilation, and maintain appropriate levels of temperature and humidity. Monitoring and addressing IAQ is crucial for creating comfortable, healthy living and working spaces.

The impact of poor indoor air quality

Health impacts

Make no mistake, poor indoor air quality can kill. World Health Organisation figures published in December 2023 show that:

  • Household air pollution was responsible for an estimated 3.2 million deaths per year in 2020, including over 237,000 deaths of children under the age of 5.
  • The combined effects of ambient air pollution and household air pollution are associated with 6.7 million premature deaths annually.
  • Household air pollution exposure leads to noncommunicable diseases including stroke, ischaemic heart disease, chronic obstructive pulmonary disease (COPD) and lung cancer.

Poor IAQ can lead to various short-term and long-term health problems, with the severity depending on the types and levels of pollutants present in the indoor air. Some common health impacts associated with poor IAQ include:

Respiratory issues: Exposure to airborne pollutants, such as particulate matter, dust, mould spores, and allergens, can irritate the respiratory system. This can lead to symptoms like coughing, wheezing, shortness of breath, and exacerbation of pre-existing respiratory conditions like asthma or COPD.

Allergies: Allergens like pollen, dust mites, pet dander, and mould can trigger allergic reactions in susceptible individuals. Symptoms may include sneezing, nasal congestion, itchy eyes, and skin rashes.

Eye, nose, and throat irritation: Volatile Organic Compounds (VOCs) such as formaldehyde, tobacco smoke, and other pollutants can cause irritation to the eyes, nose, and throat. Symptoms may include watery eyes, sore throat, and nasal congestion.

Headaches and fatigue: Poor IAQ, especially due to high levels of certain pollutants like VOCs, may contribute to headaches, dizziness, and fatigue. 

Cardiovascular issues: Long-term exposure to indoor air pollution, particularly fine particulate matter (PM2.5), has been linked to cardiovascular problems, including an increased risk of heart attacks and strokes.

Aggravation of existing conditions: Individuals with pre-existing health conditions, such as asthma, may experience worsened symptoms when exposed to poor IAQ.

Developmental and neurological effects: Some studies suggest a possible link between exposure to indoor pollutants such as lead and tobacco smoke, and adverse effects on cognitive function and development, especially in children.

Cancer: Prolonged exposure to certain indoor pollutants, such as radon and certain VOCs, has been associated with an increased risk of developing cancer.

Mental health: Those experiencing poor IAQ, related health issues, or living with / caring for those who do, can experience considerable stress. Anxiety, low mood, insomnia, and depression are all potential issues. 

The severity of health effects can vary based on factors such as individual sensitivity, age, duration of exposure, the concentration of pollutants, and the presence of underlying health conditions. According to the IAQ Matters initiative, “Using advanced filtration allows for reduction of the burden of disease by 42%.”

Social impacts

The health issues caused by poor IAQ can negatively affect performance at work or education, or ability to work and study, increasing the risk of unemployment and poverty. Those living in a home with poor IAQ are already more likely to have a low income and be living in rented accommodation, or an older property. Having the funds to fix IAQ issues, or the ability to force landlords to improve the indoor environment can be problematic.

Figures from IAQ Matters show that:

  • Over 90% of Europeans live in areas where WHO Guidelines for PM2.5 are not attained
  • Businesses experience a 5% loss of work performance caused by poor air quality due to increased pollution load/decreased ventilation
  • The cost of providing a good indoor air quality in office buildings is less than 1% of the labour cost
  • A boost of work performance by 5% means:
    • 25 minutes longer in the working day
    • Reduced number of breaks in work
    • 10 sick leave days less during the year
  • More than half of 742 classrooms investigated in Denmark were inadequately ventilated
  • Good IAQ helps schools reach their primary goal of educating children
  • Increase of learning performance by 12% means one more year of education for your child.

Not only that, but it makes sound financial sense to invest in good IAQ. This is because:

  • Labour cost is from 25 to 100 times higher than energy cost
  • Labour cost is from 25 to 100 times higher than maintenance cost
  • Labour cost is roughly 4 to 15 times higher than renting cost
  • Labour cost is roughly 4 to 40 times higher than construction costs.


Sick building syndrome

The phenomenon of sick building syndrome is mainly, but not exclusively, experienced in office buildings, particularly those with open-plan layouts. It is the name for symptoms that appear while you are in a particular building. Symptoms get worse the longer you stay in the building and improve when you leave. Symptoms can include: 
•    Respiratory issues
•    Allergies
•    Eye, nose, and throat irritation
•    Headaches and fatigue
•    Aggravation of existing conditions.

Sick building syndrome is likely to be caused by a combination of:
•    Poor ventilation
•    Poor maintenance of HVAC systems
•    Air pollution
•    Unsuitable lighting
•    Ineffective cleaning
•    Poor layout – crowded areas.

Using efficient, effective, well maintained HVAC systems can be key to solving issues with sick building syndrome.


Common indoor air pollutants

Common indoor air pollutants include:

Particulate Matter (PM): Tiny particles suspended in the air, responsible for the most IAQ related deaths.

  • Inert particles of 0.3 µm to 0.5 µm size include tobacco, combustion, ultrafine and fine particles.
  • Inert particles of 1.0 µm to 2.0 µm size include pollen, tobacco, cooking, household, comprised of particles such as soot carbon (black carbon) and organic carbon, biomass combustion (wood) and road transport.
  • Inert particles of 3.0 µm to 5.0 µm size include wood heating, construction, industry, crops (ploughing), diesel road transport and dust (roads, breaks, tyres).

Volatile Organic Compounds (VOCs): Gases emitted from certain solids or liquids, commonly found in household products.

  • Acetone gas includes household products, solvents, and paints.
  • Acetaldehyde gas includes tobacco smoke, raw woods and particleboard, insulation materials, atmospheric photochemistry, and metabolite of ethyl alcohol.
  • Heptane gas includes flue gasses and car pollution.
  • Toluene gas includes solvents for paint, varnishes and coatings, rubber, polystyrene, fats, waxes, and resins.
  • Formaldehyde gas includes particleboard, fibreboard, glue of agglomerated wooden panels, emissions from new books and magazines, paints in the ‘solvent’ phase and tobacco smoke.

Natural gases: Naturally occurring gases, including those from appliances.

  • Carbon Monoxide (CO) gas produced by incomplete combustion of fossil fuels.
  • Radon gas is a naturally occurring radioactive gas that can enter buildings through the ground.

Mould and mildew: Fungi that develop because of the indoor environment.

  • Microorganisms that can grow in damp or humid conditions, leading to respiratory issues.
  • Fungi in natural substrates (soil, wood, wax, water), vegetables, fresh and dried fruits, manufactured products (cosmetic emulsion, plastics, photography, leather, rubber, electronic components, metals, paper, wall or artistic paint, textiles, varnish).

Biological contaminants: Pollutants that can cause infectious disease, allergy, and inflammatory responses.

  • Bacteria and viruses
  • Pet dander, dust mites, pollen
  • Other microorganisms.

While this is not an exhaustive list, it shows the vast array of indoor pollutants in buildings. 

Improving indoor air quality

To minimise health risks, it is crucial to address and improve indoor air quality by:

1)    Identifying and mitigating pollution sources:
a.    Combustion appliances
b.    Building materials and furnishings
c.    Household cleaning products
d.    Pesticides
e.    Mould and mildew
f.    Cooking
g.    Radon gas
h.    Dust
i.    Pet dander
j.    Biological contaminants

2)    Ensuring appropriate use of HVAC systems:
a.    Ventilation
b.    Air filtration / purification
c.    Heating / cooling
d.    Dehumidification

3)    Improving the building envelope:
a.    Windows
b.    Insulation
c.    Draught-proofing
d.    Identify and fix leaks
e.    Address damp course issues. 

4)    Adopting good indoor air quality practices:
a.    Regular maintenance of HVAC systems
b.    Proper cleaning
c.    Ceasing activities that contribute to poor IAQ such as smoking cigarettes, burning candles or drying washing indoors.

Ironically, in our bid to decarbonised buildings the number of properties affected by poor IAQ is likely to rise. This will be a particular issue in residential buildings, where older building stock is retrofitted with sustainable heating systems requiring energy efficiency improvements to the building envelope. Airtight buildings may save on energy by trapping in heat, but they also trap indoor pollutants. Therefore, if ventilation systems are inadequate, poor IAQ will pose a threat.

The role of HVAC in indoor air quality

HVAC systems play a crucial role in maintaining good indoor air quality.

Ventilation systems are designed to bring in fresh outdoor air and distribute it throughout the building. Ventilation systems also remove stale air, odours, and contaminants from the indoor environment. Adequate ventilation can eliminate issues such as condensation, damp, and mould.

HVAC systems such as Air Handling Units (AHUs) and ventilation systems are equipped with air filters that capture dust, pollen, mould spores, and other particulate matter. They can be used at different stages of air treatment and come in a range of designs and classes. Air filters remove harmful particles from the air and improve overall air quality.

Humidity control
HVAC systems help control indoor humidity levels. Maintaining appropriate humidity levels inhibits the growth of mould and dust mites, both of which can negatively impact air quality. In dry climates, HVAC systems can also add moisture to the air to prevent issues related to overly dry indoor environments.

Temperature control
HVAC systems regulate indoor temperatures, creating a comfortable environment for occupants. This, in turn, contributes to well-being and productivity.

Air cleaning technologies (purification)
Air cleaners can improve indoor air quality by collecting and/or destroying (partially or fully) a wide range of air pollutants. Air cleaners both circulate and filter the air. 

Monitoring and control
Modern HVAC systems often include smart features and sensors that allow for real-time monitoring and control of indoor air quality parameters, enabling adjustments based on specific needs. This ensures systems work as efficiently and effectively as possible and can alert end users of any issues.

Regular maintenance
Routine maintenance, including regular filter replacement, ensures that HVAC systems operate efficiently in capturing and preventing the circulation of contaminants. Regular cleaning of HVAC components (including ducts) prevents the accumulation of dust, mould, and other pollutants.

Choosing the right HVAC products for superior IAQ

HVAC systems are integral to maintaining good indoor air quality by providing ventilation, filtration, purification, humidity control, and temperature regulation. However, not all products are equal when it comes to performance or energy efficiency. Third-party certification ensures that products perform exactly as expected, and enable product selection based on verified performance data. Eurovent Certita Certification runs Eurovent Certified Performance programmes for products that improve indoor air quality, for homes and buildings including:

Certification for homes:

Certification for buildings:

These programmes ensure that products live up to their hype, providing HVAC professionals, buyers and end users with the assurance that IAQ deliverables will be met. It’s free to use Eurovent’s certified product directory to search for, and compare, a wide range of HVAC products.

Search for certified products now


The IAQ Matters initiative brings together HVAC manufacturers in Europe and the Middle East, to provide solutions to ensure a healthy indoor climate. 

Visit the IAQ Matters website