Improve indoor air quality in 7 steps

Indoor air quality has a direct impact on comfort, performance and the condition of buildings. Yet it is often underestimated in everyday life. Especially in modern, airtight buildings, traditional window ventilation is often no longer sufficient to ensure consistently optimal indoor air quality.

Anyone looking to improve air quality does not need complex concepts, but clear, practical measures. What matters is the interaction between air exchange, humidity control and the reduction of pollutants.

This guide explains which factors are truly decisive and how indoor air quality in apartments and buildings can be improved in a targeted way.

 

Why poor indoor air quality is an underestimated problem

Poor indoor air quality often only becomes noticeable when complaints arise or structural damage becomes visible. Many issues develop gradually and remain unnoticed for a long time.

Typical signs of poor indoor air

• stale or stuffy air
• increased humidity
• condensation on windows
• musty odours
• concentration problems
• recurring moisture damage or mould

These symptoms usually indicate that air exchange is insufficient and that pollutants or moisture are accumulating.

 

Why ventilation alone is often not enough

Window ventilation only works reliably if it is carried out consistently and correctly. In practice, this often fails due to:

• irregular ventilation behaviour
• lack of time in everyday life
• incorrect ventilation techniques
• airtight building envelopes

Especially in renovated or new buildings, this quickly leads to an imbalance between humidity, air exchange and usage. In the long term, this negatively affects indoor air quality.

 

The most common causes of poor indoor air quality

Anyone who wants to improve air quality must first understand the causes. In practice, problems rarely arise from a single factor, but from the interaction of several influences.

Humidity and mould growth

Humidity is one of the most common triggers of poor indoor air quality. It is caused by:

• cooking
• showering
• drying laundry
• occupants’ breathing

If this moisture is not sufficiently removed, indoor humidity rises permanently.

The consequences:

• condensation on windows and walls
• mould growth
• unpleasant odours
• long-term structural damage

A critical point is reached when moist air regularly meets cold surfaces.

 

Pollutants from materials and furniture

Many indoor environments contain materials that continuously release substances into the indoor air .

Typical sources:

• furniture and wood-based materials
• paints and varnishes
• floor coverings
• cleaning products

These so-called VOCs (volatile organic compounds) can accumulate in poorly ventilated spaces and significantly reduce air quality.

 

CO₂ and insufficient air exchange

An often underestimated factor is the CO₂ level in indoor spaces. Even under normal use, it rises quickly.

Typical effects:

• fatigue
• concentration problems
• reduced performance

The cause is almost always insufficient air exchange. Especially in airtight buildings without controlled ventilation, indoor air can quickly feel “used” even without obvious pollutants.

 

Improving air quality: 7 practical measures

To sustainably improve air quality, practical and reliable measures are essential.

1. Ventilate properly and regularly

Pulse ventilation remains one of the simplest methods to replace stale air.

Important:

• ventilate several times a day
• fully open windows instead of tilting
• use cross ventilation for fast air exchange

2. Control humidity

Optimal indoor air is typically between 40–60% relative humidity .

Measures:

• use hygrometers
• remove moisture loads in a targeted way
• dehumidify if necessary

3. Reduce pollutant sources

Typical measures:

use low-emission materials
choose cleaning products carefully
allow new furniture to off-gas
avoid smoke sources

4. Use air filters and air purifiers selectively

Air purifiers can be useful in specific situations:

• high particulate matter exposure
• allergies
• urban environments

However, they do not replace necessary air exchange.

5. Maintain existing ventilation systems

Existing systems lose effectiveness without regular maintenance.

This includes:

• filter replacement
• cleaning components
• functional checks

6. Improve air circulation

In many rooms, stagnant air zones develop.

Helpful measures:

• keep airflow paths clear
• avoid blocked ventilation openings
• optimise room layout

7. Decentralised ventilation systems as a long-term solution

If manual ventilation is unreliable, a technical solution is required.

Decentralised ventilation systems with heat recovery (HRV) ensure:

• continuous air exchange
• controlled removal of humidity
• stable indoor air quality independent of user behaviour

 

 

When a ventilation solution becomes necessary

Limits of window ventilation

Window ventilation is highly user-dependent and therefore unreliable in the long term.

Typical issues:

• inconsistent ventilation behaviour
• heat loss in winter
• lack of control over air volumes
• no targeted moisture removal

 

Advantages of modern ventilation systems

Modern systems operate independently of user behaviour and ensure continuous fresh air supply .

Key benefits:

• constant fresh air supply
• controlled moisture removal
• reduction of CO₂ and pollutants
• protection against mould

Energy efficiency and heat recovery

Modern systems use heat recovery (HRV) :

• exhaust air is removed
• heat is recovered
• fresh air is preheated

Result:

• stable indoor air quality
• reduced energy consumption
• improved indoor climate

 

Conclusion: Good indoor air quality can be planned

Improving indoor air quality does not require starting from scratch. The key factors are known and can be controlled effectively.

In short:

• air exchange is the foundation
• humidity must be controlled
• pollutants should be reduced
• manual measures reach their limits quickly

In many buildings, only a well-designed ventilation solution ensures consistently stable conditions. It provides continuous fresh air supply while protecting the building structure.

This makes good indoor air quality not a matter of chance, but a predictable and sustainable outcome.