Indoor Air Quality Issues — Identify, Prevent, and Fix

Indoor air quality issues can manifest in many ways. The most common symptoms are headaches, fatigue, difficulty concentrating, eye and skin irritation, and respiratory symptoms. Symptoms may ease when leaving the building — this is one of the clearest signs of an indoor air problem.

Long-term exposure to poor indoor air can lead to more serious health effects. Chronic exposure to mold and microbial air can cause asthma, allergies, and other respiratory diseases. Children, the elderly, and people with allergies are especially sensitive to indoor air contaminants.

Typical building-related symptoms:

• Mild symptoms: Stuffy feeling, dry skin, itchy eyes, mild headache
• Moderate symptoms: Recurring runny nose, cough, throat irritation, fatigue, insomnia
• Severe symptoms: Asthma-like symptoms, recurring respiratory infections, prolonged cough, skin rash

If multiple family members experience symptoms in the same space and the symptoms ease when they are elsewhere, there is reason to suspect a building-related indoor air problem, and the cause should be investigated.

Inadequate ventilation is the most common cause of poor indoor air. When air doesn't circulate sufficiently, carbon dioxide, moisture, and contaminants accumulate. Dirty ventilation ducts and old filters further weaken ventilation. Particularly in homes from the 1970s–1990s, gravity-based ventilation often doesn't meet the demands of current occupancy levels.

Moisture damage and mold problems are a serious indoor air risk. Moisture can accumulate in structures due to inadequate ventilation, roof leaks, drainage deficiencies, or pipe breaks. Mold produces spores and metabolic byproducts that cause health effects even in small concentrations. The most common moisture damage locations are bathrooms, basements, subfloor spaces, and attics.

Radon is an odorless and invisible radioactive gas that rises from the ground into a building's indoor air. In Finland, radon concentrations are among the highest in the world — especially in the granite-based areas of Southern Finland. The indoor air radon limit is 300 Bq/m³, and the action level for new buildings is 200 Bq/m³. Long-term exposure to high concentrations increases the risk of lung cancer.

VOC emissions (volatile organic compounds) are released from building materials, paints, adhesives, furniture, and cleaning products. Especially in new constructions and during the first months after renovation, VOC concentrations can be elevated. Other indoor air contaminants include mineral fibers, formaldehyde, and outdoor pollutants such as traffic emissions and pollen.

A functioning ventilation system is the foundation for good indoor air. In Finland, three types of ventilation are used:

• Gravity-based ventilation: Air circulates through temperature differences and wind. Common in older homes. Efficiency varies with weather conditions and is often inadequate.
• Mechanical exhaust ventilation: Contaminated air is removed by a fan; supply air enters through vents. Common in homes from the 1970s–1990s.
• Mechanical supply and exhaust ventilation (HRV): Both supply and exhaust air pass through a unit. Heat recovery saves energy. The modern and most efficient option.

Ventilation duct cleaning is recommended every 5–10 years. In uncleaned ducts, dust, grease, and microbes accumulate, which worsens air quality and increases energy consumption. Filters should be changed according to the manufacturer's instructions, usually 1–2 times per year.

The balance of air flows should be checked regularly. Unbalanced ventilation can cause negative pressure, which draws contaminants from structures into the indoor air, or positive pressure, which pushes moist indoor air into structures causing a moisture damage risk.

An indoor air measurement is the best way to determine the scope and cause of a problem. A professional measurement provides a reliable picture of the indoor air condition and guides the correct corrective measures.

Key measurement parameters and threshold values:

• Carbon dioxide (CO₂): Good level below 1,000 ppm, satisfactory 1,000–1,500 ppm, poor above 1,500 ppm. Indicates ventilation adequacy.
• Relative humidity: Target 30–45%. Below 20% causes dryness symptoms, above 60% increases mold risk.
• Temperature: Recommended 20–22 °C. Too high a temperature increases chemical emissions from materials.
• Radon: Limit 300 Bq/m³ (existing buildings), 200 Bq/m³ (new buildings).
• TVOC (total VOC): Good level below 200 µg/m³, satisfactory 200–600 µg/m³, poor above 600 µg/m³.

A professional indoor air investigation includes a sensory assessment, measurements, possible material samples, and a clear report of findings and repair recommendations. Measurements are typically conducted over a 1–7 day period during normal use, so results are representative.

The price of an indoor air measurement ranges from 250 to 800 euros depending on the scope of the investigation. A basic measurement (CO₂, humidity, temperature) is the most affordable, while a broader investigation with material samples and microbial analyses is more expensive but provides a more comprehensive picture.

Corrective measures depend on the cause and severity of the problem. Below are the most common measures in order of priority:

First steps (do immediately):

• Replace HVAC filters and clean vents
• Basic service of the ventilation unit and settings check
• Increase ventilation (cross-ventilate by opening windows for 5–10 minutes per day)
• Investigate and dry any visible moisture spots

Professional measures:

• Ventilation duct cleaning (300–800 euros) — removes accumulated dust, grease, and microbes from the duct system
• Airflow measurement and adjustment (200–400 euros) — ensures the correct ventilation level
• Supply air vent installation (100–200 euros each) — improves supply air intake, especially in gravity-based ventilation
• Moisture damage repair — scope and price depend on the size of the damage, can range from hundreds to thousands of euros
• Radon piping installation (1,500–4,000 euros) — if radon concentration exceeds the limit

Ventilation unit servicing and airflow adjustment alone can significantly improve indoor air. If the problem is caused by moisture damage, it must be repaired structurally before improving ventilation will help.

In some situations, an indoor air problem requires intervention by authorities. According to the Health Protection Act (763/1994), indoor air in a dwelling must not cause health hazards to residents.

Contact the municipal health protection authority when:

• The housing company or property owner doesn't respond to your reports of indoor air problems
• Symptoms are severe and recurring (diagnosed by a doctor)
• You suspect significant moisture damage or mold that goes uninvestigated
• The landlord doesn't repair reported indoor air problems

The health protection authority can conduct a dwelling inspection and issue the property owner a repair order. The inspection is free for the resident. The report can be made to your municipality's environmental health care.

Good to remember: document your symptoms, make a written report to the property owner, and request a written response. This documentation is important if the matter proceeds to official review or legal proceedings.

The best way to prevent indoor air problems is regular maintenance and monitoring. These measures keep indoor air quality high:

Daily:

• Ventilate the home for at least 5–10 minutes (most effective with cross-ventilation)
• Use the range hood while cooking
• Make sure ventilation vents are not blocked

Monthly:

• Check supply air vent cleanliness
• Monitor indoor humidity with a hygrometer (target 30–45%)
• Check bathroom and kitchen connections for leaks

Annually:

• Change ventilation filters 1–2 times per year
• Clean exhaust air vents (vacuum or wash)
• Check ventilation unit operation and settings
• Check basement and attic ventilation

Every 5–10 years:

• Schedule professional ventilation duct cleaning
• Have a basic indoor air quality measurement done
• Measure radon concentration (especially in Southern Finland)

Good indoor air is an investment in health. The annual cost of ventilation maintenance is typically 100–300 euros (filters and basic service), while fixing indoor air problems after the fact can cost thousands of euros.